Typical interatomic distances: organic compounds

Allen, F. H.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R.

doi:10.1107/97809553602060000621

International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

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International Tables for Crystallography (2006). Vol. C. ch. 9.5, pp. 790-811
https://doi.org/10.1107/97809553602060000621

Chapter 9.5. Typical interatomic distances: organic compounds

F. H. Allen,^a D. G. Watson,^a L. Brammer,^b A. G. Orpen^c and R. Taylor^a

^a Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, England,^bDepartment of Chemistry, University of Missouri–St Louis, 8001 Natural Bridge Road, St Louis, MO 63121-4499, USA, and ^cSchool of Chemistry, University of Bristol, Bristol BS8 1TS, England

Mean bond lengths for organic compounds, derived from the Cambridge Structural Database, are tabulated for 625 different bond types involving the elements C, H, N, O, B, F, P, S, Cl, As, Se, Br, Te and I. Associated statistical information characterizes each of the distributions, which are derived from both X-ray and neutron diffraction data.

Keywords: basic structural features; bonds; interatomic distances; organic compounds.

9.5.1. Introduction

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The determination of molecular geometry is of vital importance to our understanding of chemical structure and bonding. The majority of experimental data have come from X-ray and neutron diffraction, microwave spectroscopy, and electron diffraction. Over the years, compilations of results from these techniques have appeared sporadically. The first major compilation was Chemical Society Special Publication No. 11: Tables of Interatomic Distances and Configuration in Molecules and Ions (Sutton, 1958 ). This volume summarized results obtained by diffraction and spectroscopic methods prior to 1956; a supplementary volume (Sutton, 1965 ) extended this coverage to 1959. Summary tables of bond lengths between carbon and other elements were also published in Volume III of International Tables for X-ray Crystallography (Kennard, 1962 ). Some years later, the Cambridge Crystallographic Data Centre (Allen, Bellard, Brice, Cartwright, Doubleday, Higgs, Hummelink, Hummelink-Peters, Kennard, Motherwell, Rodgers & Watson, 1979 ) produced an atlas-style compendium of all organic, organometallic and metal-complex crystal structures published in the period 1960–1965 (Kennard, Watson, Allen, Isaacs, Motherwell, Pettersen & Town, 1972 ). More recently, a survey of geometries determined by spectroscopic methods (Harmony, Laurie, Kuczkowski, Schwendemann, Ramsay, Lovas, Lafferty & Maki, 1979 ) has extended coverage in this area to mid-1977.

The production of further comprehensive compendia of X-ray and neutron diffraction results has been precluded by the steep rise in the number of published crystal structures, as illustrated by Fig. 9.5.1.1 . Printed compilations have been effectively superseded by computerized databases. In particular, the Cambridge Structural Database now (1991) contains bibliographic, chemical, and numerical results for some 86 000 organo-carbon crystal structures. This machine-readable file fulfils the function of a comprehensive structure-by-structure compendium of molecular geometries. However, the amount of data now held in the CSD is so large that there is also a need for concise, printed tabulations of average molecular dimensions.

Figure 9.5.1.1| top | pdf |

Growth of the Cambridge Structural Database 1965–1985 as number of entries (N_ent) published in a given year.

The only tables of average geometry in general use are those contained in Sutton (1958 , 1965 ) which list mean bond lengths for a variety of atom pairs and functional groups. Since these early tables were based on data obtained before 1960, we have used the CSD to prepare a new table of average bond lengths in organic compounds. Table 9.5.1.1 given here specifically lists average lengths for bonds involving the elements H, B, C, N, O, F, Si, P, S, Cl, As, Se, Br, Te, and I. Mean values are presented for 682 different bond types involving these elements.

Table 9.5.1.1 | top | pdf |
Average lengths (Å) for bonds involving the elements H, B, C, N, O, F, Si, P, S, Cl, As, Se, Br, Te, and I

Bond	Substructure	d	m	σ	q _l	q _u	n	Note^†
As(3)—As(3)	X ₂ —As—As—X₂	2.459	2.457	0.011	2.456	2.466	8
As—B	see CUDLOC (2.065), CUDLUI (2.041)
As—Br	see CODDEE, CODDII (2.346–3.203)
As(4)—C	X ₃ —As—CH₃	1.903	1.907	0.016	1.893	1.916	12
	(X)₂(C, O, S=)As—Csp³	1.927	1.929	0.017	1.921	1.937	16
	As —C_ar in Ph₄As⁺	1.905	1.909	0.012	1.897	1.912	108
	(X)₂(C, O, S=)As—C_ar	1.922	1.927	0.016	1.908	1.934	36
As(3)—C	X ₂ —As—Csp³	1.963	1.965	0.017	1.948	1.978	6
As(3)—C	X ₂ —As—C_ar	1.956	1.956	0.015	1.944	1.964	41
As(3)—Cl	X ₂ —As—Cl	2.268	2.256	0.039	2.247	2.281	10
As(6)—F	in $[{\bf AsF}^-_6]$	1.678	1.676	0.020	1.659	1.695	36
As(3)—I	see OPIMAS (2.579, 2.590)
As(3)—N(3)	X ₂ —As—N—X₂	1.858	1.858	0.029	1.839	1.873	19
As(4)=N(2)	see TPASSN (1.837)
As(4)—O	(X)₂(O=)As—OH	1.710	1.712	0.017	1.695	1.726	6
As(3)—O	see ASAZOC, PHASOC01 (1.787–1.845)
As(4)=O	X ₃ —As=O	1.661	1.661	0.016	1.652	1.667	9
As(3)—P(3)	see BELNIP (2.350, 2.362)							^‡
As(3)=P(3)	see BUTHAZ10 (2.124)							^‡
As(3)—S	X ₂ —As—S	2.275	2.266	0.032	2.247	2.298	14
As(4)=S	X ₃ —As=S	2.083	2.082	0.004	2.080	2.086	9
As(3)—Se(2)	see COSDIX, ESEARS (2.355–2.401)							^‡
As(3)—Si(4)	see BICGEZ, MESIAD (2.351–2.365)							^‡
As(3)—Te(2)	see ETEARS (2.571, 2.576)							^‡
B(n)—B(n)	n = 5–7 in boron cages	1.775	1.773	0.031	1.763	1.786	688
B(4)—B(4)	see CETTAW (2.041)
B(4)—B(3)	see COFVOI (1.698)
B(3)—B(3)	X ₂ —B—B—X₂	1.701	1.700	0.014	1.691	1.712	8
B(6)—Br		1.967	1.971	0.014	1.954	1.979	7	^‡
B(4)—Br		2.017	2.008	0.031	1.990	2.044	15	^‡
B(n)—C	n = 5–7: B—C in cages	1.716	1.717	0.020	1.707	1.728	96
	n = 3–4: B—Csp³ not cages	1.597	1.599	0.022	1.585	1.611	29	1
	n = 4: B—C_ar	1.606	1.607	0.012	1.596	1.615	41
	n = 4: B⁻—C_ar in Ph₄B⁻	1.643	1.643	0.006	1.641	1.645	16
	n = 3: B—C_ar	1.556	1.552	0.015	1.546	1.566	24
B(n)—Cl	B (5)—Cl and B(3)—Cl	1.751	1.751	0.011	1.743	1.761	14
B(n)—Cl	B (4)—Cl	1.833	1.833	0.013	1.821	1.843	22
B(4)—F	B —F (B neutral)	1.366	1.368	0.017	1.356	1.375	25
B(4)—F	B ⁻ —F in $[{\rm BF}^-_4]$	1.365	1.372	0.029	1.352	1.390	84
B(4)—I	see TMPBTI (2.220, 2.253)
B(4)—N(3)	X ₃ —B—N(=C)(X)	1.611	1.617	0.013	1.601	1.625	8
B(4)—N(3)	in pyrazaboles	1.549	1.552	0.015	1.536	1.560	10
B(3)—N(3)	X ₂ —B—N—C₂: all coplanar	1.404	1.404	0.014	1.389	1.408	40	2
	for τ(BN) > 30° see BOGSUL, BUSHAY, CILRUK (1.434–1.530)
	S₂—B—N—X₂	1.447	1.443	0.013	1.435	1.470	14
B(4)—O	B —O in $[{\rm BO}^-_4]$	1.468	1.468	0.022	1.453	1.479	24
B(4)—O	for neutral B—O see Note 3							3
B(3)—O(2)	X ₂ —B—O—X	1.367	1.367	0.024	1.349	1.382	35
B(n)—P	n = 4: B—P	1.922	1.927	0.027	1.900	1.954	10
B(n)—P	n = 3: see BUPSIB10 (1.892, 1.893)
B(4)—S	B (4)—S(3)	1.930	1.927	0.009	1.925	1.934	10
B(4)—S	B (4)—S(2)	1.896	1.896	0.004	1.893	1.899	6
B(3)—S	N—B—S₂	1.806	1.806	0.010	1.799	1.816	28
B(3)—S	(=X—)(N—)B—S	1.851	1.854	0.013	1.842	1.859	10
Br—Br	see BEPZEB, TPASTB	2.542	2.548	0.015	2.526	2.551	4
Br—C	Br —C*	1.966	1.967	0.029	1.951	1.983	100	4
	Br —Csp³ (cyclopropane)	1.910	1.910	0.010	1.900	1.914	8
	Br —Csp²	1.883	1.881	0.015	1.874	1.894	31	4
	Br —C_ar (mono-Br + m,p-Br₂)	1.899	1.899	0.012	1.892	1.906	119	4
	Br —C_ar (o-Br₂)	1.875	1.872	0.011	1.864	1.884	8	4
⁻ Br(2)—Cl	see TEACBR (2.362–2.402)							^†
Br—I	see DTHIBR10 (2.646), TPHOSI (2.695)
Br—N	see NBBZAM (1.843)
Br—O	see CIYFOF	1.581	1.581	0.007	1.574	1.587	4
Br—P	see CISTED (2.366)
Br—S(2)	see BEMLIO (2.206)							^†
Br—S(3)	see CIWYIQ (2.435, 2.453)							^†
Br—S(3)⁺	see THINBR (2.321)							^†
Br—Se	see CIFZUM (2.508, 2.619)
Br—Si	see BIZJAV (2.284)
Br—Te	In Br₆Te²⁻see CUGBAH (2.692–2.716)
	Br —Te(4) see BETUTE10 (3.079, 3.015)
	Br —Te(3) see BTUPTE (2.835)
Csp³—Csp³	C^#—CH₂—CH₃	1.513	1.514	0.014	1.507	1.523	192
	(C^#)₂—CH—CH₃	1.524	1.526	0.015	1.518	1.534	226
	(C^#)₃—C—CH₃	1.534	1.534	0.011	1.527	1.541	825
	C^#—CH₂—CH₂—C^#	1.524	1.524	0.014	1.516	1.532	2459
	(C^#)₂—CH—CH₂—C^#	1.531	1.531	0.012	1.524	1.538	1217
	(C^#)₃—C—CH₂—C^#	1.538	1.539	0.010	1.533	1.544	330
	(C^#)₂—CH—CH—(C^#)₂	1.542	1.542	0.011	1.536	1.549	321
	(C^#)₃—C—CH—(C^#)₂	1.556	1.556	0.011	1.549	1.562	215
	(C^#)₃—C—C—(C^#)₃	1.588	1.580	0.025	1.566	1.610	21
	C* —C* (overall)	1.530	1.530	0.015	1.521	1.539	5777	5, 6
	in cyclopropane (any substituent)	1.510	1.509	0.026	1.497	1.523	888	7
	in cyclobutane (any substituent)	1.554	1.553	0.021	1.540	1.567	679	8
	in cyclopentane (C,H substituents)	1.543	1.543	0.018	1.532	1.554	1641
	in cyclohexane (C,H substituents)	1.535	1.535	0.016	1.525	1.545	2814
	cyclopropyl—C* (exocyclic)	1.518	1.518	0.019	1.505	1.531	366	7
	cyclobutyl—C* (exocyclic)	1.529	1.529	0.016	1.519	1.539	376	8
	cyclopentyl—C* (exocyclic)	1.540	1.541	0.017	1.527	1.549	956
	cyclohexyl—C* (exocyclic)	1.539	1.538	0.016	1.529	1.549	2682
	in cyclobutene (any substituent)	1.573	1.574	0.017	1.566	1.586	25	8
	in cyclopentene (C,H substituents)	1.541	1.539	0.015	1.532	1.549	208
	in cyclohexene (C,H substituents)	1.541	1.541	0.020	1.528	1.554	586
	in oxirane (epoxide)	1.466	1.466	0.015	1.458	1.474	249	9
	in aziridine	1.480	1.481	0.021	1.465	1.496	67	9
	in oxetane	1.541	1.541	0.019	1.527	1.557	16
	in azetidine	1.548	1.543	0.018	1.536	1.558	22
	oxiranyl—C* (exocyclic)	1.509	1.507	0.018	1.497	1.519	333	9
	aziridinyl—C* (exocyclic)	1.512	1.512	0.018	1.496	1.526	13	9
Csp³—Csp²	C H₃—C=C	1.503	1.504	0.011	1.497	1.509	215
	C^#—CH₂—C=C	1.502	1.502	0.013	1.494	1.510	483
	(C^#)₂—CH—C=C	1.510	1.510	0.014	1.501	1.518	564
	(C^#)₃—C—C=C	1.522	1.522	0.016	1.511	1.533	193
	C *—C=C (overall)	1.507	1.507	0.015	1.499	1.517	1456	5
	C *—C=C (endocylic):
	in cyclopropene	1.509	1.508	0.016	1.500	1.516	20	10
	in cyclobutene	1.513	1.512	0.018	1.500	1.525	50	8
	in cyclopentene	1.512	1.512	0.014	1.502	1.521	208
	in cyclohexene	1.506	1.505	0.016	1.495	1.516	391
	in cyclopentadiene	1.502	1.503	0.019	1.490	1.515	18
	in cyclohexa-1,3-diene	1.504	1.504	0.017	1.491	1.517	56
	C* —C≡C (exocyclic):
	cyclopropenyl—C*	1.478	1.475	0.012	1.470	1.485	7	10
	cyclobutenyl—C*	1.489	1.483	0.015	1.479	1.496	11	8
	cyclopentenyl—C*	1.504	1.506	0.012	1.495	1.512	115
	cyclohexenyl—C*	1.511	1.511	0.013	1.502	1.519	292
	C* —CH=O in aldehydes	1.510	1.510	0.008	1.501	1.518	7
	(C*)₂—C=O in ketones	1.511	1.511	0.015	1.501	1.521	952	11
	(C*)₂—C=O in cyclobutanone	1.529	1.530	0.016	1.514	1.545	18
	(C*)₂—C=O in cyclopentanone	1.514	1.514	0.016	1.505	1.523	312
	(C*)₂—C=O acyclic and 6+ rings	1.509	1.509	0.016	1.499	1.519	626
	C *—COOH in carboxylic acids	1.502	1.502	0.014	1.495	1.510	176
	C *—COO⁻ in carboxylate anions	1.520	1.521	0.011	1.516	1.528	57
	C —C(=O)(—OC) in acyclic esters	1.497	1.496	0.018	1.484	1.509	553	12
	C —C(=O)(—OC) in β-lactones	1.519	1.519	0.020	1.500	1.538	4	13
	C —C(=O)(—OC) in γ-lactones	1.512	1.512	0.015	1.501	1.521	110	12
	C —C(=O)(—OC) in δ-lactones	1.504	1.502	0.013	1.495	1.517	27	12
	cyclopropyl (C)—C=O in ketones, acids, and esters	1.486	1.485	0.018	1.474	1.497	105	7
	C* —C(=O)(—NH₂) in acyclic amides	1.514	1.512	0.016	1.506	1.526	32	14
	C* —C(=O)(—NHC*) in acyclic amides	1.506	1.505	0.012	1.498	1.515	78	14
	C* —C(=O)[—N(C*)₂] in acyclic amides	1.505	1.505	0.011	1.496	1.517	15	14
Csp³—C_ar	C H₃—C_ar	1.506	1.507	0.011	1.501	1.513	454
	C^#—CH₂—C_ar	1.510	1.510	0.009	1.505	1.516	674
	(C^#)₂—C—C_ar	1.515	1.515	0.011	1.508	1.522	363
	(C^#)₃—C—C_ar	1.527	1.530	0.016	1.517	1.539	308
	C* —C_ar (overall)	1.513	1.513	0.014	1.505	1.521	1813
	cyclopropyl (C)—C_ar	1.490	1.490	0.015	1.479	1.503	90	7
Csp³—Csp¹	C *—C≡C	1.466	1.465	0.010	1.460	1.469	21	15
	C ^# —C≡C	1.472	1.472	0.012	1.464	1.481	88	15
	C *—C≡N	1.470	1.469	0.013	1.463	1.479	106	7(b)
	cyclopropyl (C)—C≡N	1.444	1.447	0.010	1.436	1.451	38	7
Csp²—Csp²	C=C—C=C (conjugated)	1.455	1.455	0.011	1.447	1.463	30	16, 18
	C=C—C=C (unconjugated)	1.478	1.476	0.012	1.470	1.479	8	17, 18
	C=C—C=C (overall)	1.460	1.460	0.015	1.450	1.470	38
	C=C—C=C—C=C	1.443	1.445	0.013	1.431	1.454	29	18
	C=C—C=C (endocyclic in TCNQ)	1.432	1.433	0.012	1.424	1.441	280	19
	C=C—C(=O)(—C*) (conjugated)	1.464	1.462	0.018	1.453	1.476	211	16, 18
	C=C—C(=O)(—C*) (unconjugated)	1.484	1.486	0.017	1.475	1.497	14	17, 18
	C=C—C(=O)(—C*) (overall)	1.465	1.462	0.018	1.453	1.478	226
	C=C—C(=O)—C=C:
	in benzoquinone (C,H substituents only)	1.478	1.476	0.011	1.469	1.488	28
	in benzoquinone (any substituent)	1.478	1.478	0.031	1.464	1.498	172
	non-quinonoid	1.456	1.455	0.012	1.447	1.464	28
	C—C—COOH	1.475	1.476	0.015	1.461	1.488	22
	C=C—COOC*	1.488	1.489	0.014	1.478	1.497	113
	C=C—COO⁻	1.502	1.499	0.017	1.488	1.510	11
	HOOC—COOH	1.538	1.537	0.007	1.535	1.541	9
	HOOC—COO⁻	1.549	1.552	0.009	1.546	1.553	13
	⁻ OOC—COO⁻	1.564	1.559	0.022	1.554	1.568	9
	formal Csp²—Csp² single bond in selected, non-fused heterocycles:
	in 1H-pyrrole (C3—C4)	1.412	1.410	0.016	1.401	1.427	29
	in furan (C3—C4)	1.423	1.423	0.016	1.412	1.433	62
	in thiophene (C3—C4)	1.424	1.425	0.015	1.415	1.433	40
	in pyrazole (C3—C4)	1.410	1.412	0.016	1.400	1.418	20
	in isoxazole (C3—C4)	1.425	1.425	0.016	1.413	1.438	9
	in furazan (C3—C4)	1.428	1.427	0.007	1.422	1.435	6
	in furoxan (C3—C4)	1.417	1.417	0.006	1.412	1.422	14
Csp²—C_ar	C=C—C_ar (conjugated)	1.470	1.470	0.015	1.463	1.480	37	16, 18
	C=C—C_ar (unconjugated)	1.488	1.490	0.012	1.480	1.496	87	17, 18
	C=C—C_ar (overall)	1.483	1.483	0.015	1.472	1.494	124
	cyclopropenyl (C=C)—C_ar	1.447	1.448	0.006	1.441	1.452	8	10
	C _ar —C(=O)—C*	1.488	1.489	0.016	1.478	1.500	84
	C _ar —C(=O)—C_ar	1.480	1.481	0.017	1.468	1.494	58
	C _ar —COOH	1.484	1.485	0.014	1.474	1.491	75
	C _ar —C(=O)(—OC*)	1.487	1.487	0.012	1.480	1.494	218
	C _ar —COO⁻	1.504	1.509	0.014	1.495	1.512	26
	C _ar —C(=O)—NH₂	1.500	1.503	0.020	1.498	1.510	19
	C _ar —C=N—C^# (conjugated)	1.476	1.478	0.014	1.466	1.486	27	16
	C _ar —C=N—C^# (unconjugated)	1.491	1.490	0.008	1.485	1.496	48	17
	C _ar —C=N—C^# (overall)	1.485	1.487	0.013	1.481	1.493	75
	in indole (C3—C3a)	1.434	1.434	0.011	1.428	1.439	40
Csp²—Csp¹	C=C—C≡C	1.431	1.427	0.014	1.425	1.441	11	7(b)
Csp²—Csp¹	C=C—C≡N in TCNQ	1.427	1.427	0.010	1.420	1.433	280	19
C_ar—C_ar	in biphenyls (ortho substituent all H)	1.487	1.488	0.007	1.484	1.493	30
C_ar—C_ar	( $[\ge 1]$ non-H ortho substituent)	1.490	1.491	0.010	1.486	1.495	212
C_ar—Csp¹	C _ar —C≡C	1.434	1.436	0.006	1.430	1.437	37
C_ar—Csp¹	C _ar —C≡N	1.443	1.444	0.008	1.436	1.448	31
Csp¹—Csp¹	C≡C—C≡C	1.377	1.378	0.012	1.374	1.384	21
Csp²=Csp²	C*—CH=CH₂	1.299	1.300	0.027	1.280	1.311	42
	(C*)₂—C=CH₂	1.321	1.321	0.013	1.313	1.328	77
	C—CH=CH—C (cis)	1.317	1.318	0.013	1.310	1.323	106
	C—CH=CH—C (trans)	1.312	1.311	0.011	1.304	1.320	19
	C—CH=CH—C (overall)	1.316	1.317	0.015	1.309	1.323	127
	(C)₂—C=CH—C	1.326	1.328	0.011	1.319	1.334	168
	(C)₂—C=C—(C)₂	1.331	1.330	0.009	1.326	1.334	89
	(C,H)₂—C=C—(C,H)₂ (overall)	1.322	1.323	0.014	1.315	1.331	493	5
	in cyclopropene (any substituent)	1.294	1.288	0.017	1.284	1.302	10	10
	in cyclobutene (any substituent)	1.335	1.335	0.019	1.324	1.347	25	8
	in cyclopentene (C,H substituents)	1.323	1.324	0.013	1.314	1.331	104
	in cyclohexene (C,H substituents)	1.326	1.325	0.012	1.318	1.334	196
	C =C=C (allenes, any substituents)	1.307	1.307	0.005	1.303	1.310	18
	C =C—C=C (C,H substituents, conjugated)	1.330	1.330	0.014	1.322	1.338	76	16
	C =C—C=C—C=C (C,H substituents, conjugated)	1.345	1.345	0.012	1.337	1.350	58	16
	C =C—C_ar (C,H substituents, conjugated)	1.339	1.340	0.011	1.334	1.346	124	16
	C =C in cyclopenta-1,3-diene (any substituent)	1.341	1.341	0.017	1.328	1.356	18
	C =C in cyclohexa-1,3-diene (any substituent)	1.332	1.332	0.013	1.323	1.341	56
	in C=C—C=O (C,H substituent, conjugated)	1.340	1.340	0.013	1.332	1.348	211	16, 18
	in C=C—C=O (C,H substituent, unconjugated)	1.331	1.330	0.008	1.326	1.339	14	17, 18
	in C=C—C=O (C,H substituent, overall)	1.340	1.339	0.013	1.332	1.348	226
	in cyclohexa-2,5-dien-1-ones	1.329	1.327	0.011	1.321	1.335	28
	in p-benzoquinones (C*,H substituents)	1.333	1.337	0.011	1.325	1.338	14
	in p-benzoquinones (any substituent)	1.349	1.339	0.030	1.330	1.364	86
	in TCNQ (endocyclic)	1.352	1.353	0.010	1.345	1.358	142	19
	in TCNQ (exocyclic)	1.392	1.391	0.017	1.379	1.405	139	19
	C =C—OH in enol tautomers	1.362	1.360	0.020	1.349	1.370	54
	in heterocycles (any substituent)
	1H-pyrrole (C2—C3, C4—C5)	1.375	1.377	0.018	1.361	1.388	58
	furan (C2—C3, C4—C5)	1.341	1.342	0.021	1.329	1.351	125
	thiophene (C2—C3, C4—C5)	1.362	1.359	0.025	1.346	1.377	60
	pyrazole (C4—C5)	1.369	1.372	0.019	1.362	1.383	20
	imidazole (C4—C5)	1.360	1.361	0.014	1.352	1.367	44
	isoxazole (C4—C5)	1.341	1.336	0.012	1.331	1.355	9
	indole (C2—C3)	1.364	1.363	0.012	1.355	1.371	40
C_ar $[\ddb]$ C_ar	in phenyl rings with C*,H substituents only:
	H—C $[\ddb]$ C—H	1.380	1.381	0.013	1.372	1.388	2191
	C*—C $[\ddb]$ C—H	1.387	1.388	0.010	1.382	1.393	891
	C—C $[\ddb]$ C—C	1.397	1.397	0.009	1.392	1.403	182
	C $[\ddb]$ C (overall)	1.384	1.384	0.013	1.375	1.391	3264
	F—C $[\ddb]$ C—F	1.372	1.374	0.011	1.366	1.380	84	4
	Cl—C $[\ddb]$ C—Cl	1.388	1.389	0.014	1.380	1.398	152	4
	in naphthalene (D_2h) C1—C2	1.364	1.364	0.014	1.356	1.373	440
	(any substituent) C2—C3	1.406	1.406	0.014	1.397	1.415	218
	(any substituent) C1—C8a	1.420	1.419	0.012	1.412	1.426	440
	(any substituent) C4a—C8a	1.422	1.424	0.011	1.417	1.429	109
	in anthracene (D_2h) C1—C2	1.356	1.356	0.009	1.350	1.360	56
	(any substituent) C2—C3	1.410	1.410	0.010	1.401	1.416	34
	(any substituent) C1—C9a	1.430	1.430	0.006	1.426	1.434	56
	(any substituent) C4a—C9a	1.435	1.436	0.007	1.429	1.440	34
	(any substituent) C9—C9a	1.400	1.402	0.009	1.395	1.406	68
	in pyridine (C,H substituent)	1.379	1.381	0.012	1.371	1.387	276	20
	in pyridine (any substituents)	1.380	1.380	0.015	1.371	1.389	537	20
	in pyridinium cation:
	(N⁺—H; C,H substituents on C) C2—C3	1.373	1.375	0.012	1.368	1.380	30
	(N⁺—H; C,H substituents on C) C3—C4	1.379	1.380	0.011	1.371	1.388	30
	(N⁺—X; C,H substituents on C) C2—C3	1.373	1.372	0.019	1.362	1.382	151
	(N⁺—X; C,H substituents on C) C3—C4	1.383	1.385	0.019	1.372	1.394	151
	in pyrazine (H substituent on C)	1.379	1.377	0.010	1.370	1.388	10
	in pyrazine (any substituent on C)	1.405	1.405	0.024	1.388	1.420	60
	in pyrimidine (C,H substituents on C)	1.387	1.389	0.018	1.379	1.400	28
Csp¹≡Csp¹	X —C≡C—X	1.183	1.183	0.014	1.174	1.193	119	15
	C,H—C≡C—C,H	1.181	1.181	0.014	1.173	1.192	104	15
	in C≡C—C(sp², ar)	1.189	1.193	0.010	1.181	1.195	38	15
	in C≡C—C≡C	1.192	1.192	0.010	1.187	1.197	42	15
	in CH≡C—C^#	1.174	1.174	0.011	1.167	1.180	42	15
Csp³—Cl	Omitting 1,2-dichlorides:
	C—CH₂—Cl	1.790	1.790	0.007	1.783	1.795	13	4
	C₂—CH—Cl	1.803	1.802	0.003	1.800	1.807	8	4
	C₃—C—Cl	1.849	1.856	0.011	1.837	1.858	5	4
	X—CH₂—Cl (X = C,H,N,O)	1.790	1.791	0.011	1.783	1.797	37	4
	X₂—CH—Cl (X = C,H,N,O)	1.805	1.803	0.014	1.800	1.812	26	4
	X₃—C—Cl (X = C,H,N,O)	1.843	1.838	0.014	1.835	1.858	7	4
	X₂—C—Cl₂ (X = C,H,N,O)	1.779	1.776	0.015	1.769	1.790	18	4
	X—C—Cl₃ (X = C,H,N,O)	1.768	1.765	0.011	1.761	1.776	33	4
	Cl—CH(—C)—CH(—C)—Cl	1.793	1.793	0.013	1.786	1.800	66	4
	Cl—C(—C₂)—C(—C₂)—Cl	1.762	1.760	0.010	1.757	1.765	54	4
	cyclopropyl—Cl	1.755	1.756	0.011	1.749	1.763	64
Csp²—Cl	C=C—Cl (C,H,N,O substituents on C)	1.734	1.729	0.019	1.719	1.748	63	4
	C=C—Cl₂ (C,H,N,O substituents on C)	1.720	1.716	0.013	1.708	1.729	20	4
	Cl —C=C—Cl	1.713	1.711	0.011	1.705	1.720	80	4
C_ar—Cl	C _ar —Cl (mono-Cl + m,p-Cl₂)	1.739	1.741	0.010	1.734	1.745	340	4
C_ar—Cl	C _ar —Cl (o-Cl₂)	1.720	1.720	0.010	1.713	1.717	364	4
Csp¹—Cl	see HCLENE10 (1.634, 1.646)
Csp³—F	Omitting 1,2-difluorides:
	C—CH₂—F and C₂—CH—F	1.399	1.399	0.017	1.389	1.408	25	4
	C₃—C—F	1.428	1.431	0.009	1.421	1.435	11	4
	(C*,H)₂—C—F₂	1.349	1.347	0.012	1.342	1.356	58	4
	C*—C—F₃	1.336	1.334	0.007	1.330	1.344	12	4
	F—C—C—F	1.371	1.374	0.007	1.362	1.375	26	4
	X₃—C—F (X = C,H,N,O)	1.386	1.389	0.033	1.373	1.408	70	4
	X₂—C—F₂ (X = C,H,N,O)	1.351	1.349	0.013	1.342	1.356	58	4
	X—C—F₃ (X = C,H,N,O)	1.322	1.323	0.015	1.314	1.332	309	4
	F—C(—X)₂—C(—X)₂—F (X = C,H,N,O)	1.373	1.374	0.009	1.362	1.377	30	4
	F—C(—X)₂—NO₂ (X = any substituent)	1.320	1.319	0.009	1.312	1.327	18
Csp²—F	C=C—F (C,H,N,O substituents on C)	1.340	1.340	0.013	1.334	1.346	34	4
C_ar—F	C _ar —F (mono-F + m,p-F₂)	1.363	1.362	0.008	1.357	1.368	38	4
C_ar—F	C _ar —F (o-F₂)	1.340	1.340	0.009	1.336	1.344	167	4
Csp³—H	C—C—H₃ (methyl)	1.059	1.061	0.030	1.039	1.083	83	21
	C₂—C—H₂ (primary)	1.092	1.095	0.013	1.088	1.099	100	21
	C₃—C—H (secondary)	1.099	1.097	0.004	1.095	1.103	14	21
	C_2,3—C—H (primary and secondary)	1.093	1.095	0.012	1.089	1.100	118	21
	X —C—H₃ (methyl)	1.066	1.074	0.028	1.049	1.087	160	21
	X ₂ —C—H₂ (primary)	1.092	1.095	0.012	1.088	1.099	230	21
	X ₃ —C—H (secondary)	1.099	1.099	0.007	1.095	1.103	117	21
	X _2,3 —C—H (primary and secondary)	1.094	1.096	0.011	1.091	1.100	348	21
Csp²—H	C—C=C—H	1.077	1.079	0.012	1.074	1.085	14	21
C_ar—H	C _ar —H	1.083	1.083	0.011	1.080	1.087	218	21
Csp³—I	C* —I	2.162	2.159	0.015	2.149	2.179	15	4
C_ar—I	C _ar —I	2.095	2.095	0.015	2.089	2.104	51	4
Csp³—N(4)	C* —NH	1.488	1.488	0.013	1.482	1.495	298
	*(C)** ₂ —NH	1.494	1.493	0.016	1.484	1.503	249
	*(C)** ₃ —NH⁺	1.502	1.502	0.015	1.491	1.512	509
	*(C)** ₄ —N⁺	1.510	1.509	0.020	1.496	1.523	319
	C* —N⁺ (overall)	1.499	1.498	0.018	1.488	1.510	1370
Csp³—N(3)	C* —N⁺ in N-substituted pyridinium	1.485	1.484	0.009	1.477	1.490	32
	C* —NH₂ (Nsp³: pyramidal)	1.469	1.470	0.010	1.462	1.474	19	22
	*(C)** ₂ —NH (Nsp³: pyramidal)	1.469	1.467	0.012	1.461	1.477	152	5, 22
	*(C)** ₃ —N (Nsp³: pyramidal)	1.469	1.468	0.014	1.460	1.476	1042	5, 22
	C* —Nsp³ (overall)	1.469	1.468	0.014	1.460	1.476	1201
	C sp ³ —Nsp³ in aziridine	1.472	1.471	0.016	1.464	1.482	134
	C sp ³ —Nsp³ in azetidine	1.484	1.481	0.018	1.472	1.495	21
	C sp ³ —Nsp³ in tetrahydropyrrole	1.475	1.473	0.016	1.464	1.483	66
	C sp ³ —Nsp³ in piperidine	1.473	1.473	0.013	1.460	1.479	240
	Csp³—Nsp² (N planar) in:							23
	acyclic amides C*—NH—C=O	1.454	1.451	0.011	1.446	1.461	78	14
	β-lactams C—N(—X)—C=O (endo*)	1.464	1.465	0.012	1.458	1.475	23	13
	γ-lactams C—NH—C=O (endo*)	1.457	1.458	0.011	1.449	1.465	20	13
	γ-lactams C—N(—C)—C=O (endo)	1.462	1.461	0.010	1.453	1.466	15	13
	γ-lactams C—N(—C)—C=O (exo)	1.458	1.456	0.014	1.448	1.465	15	13
	δ-lactams C—NH—C=O (endo*)	1.478	1.472	0.016	1.467	1.491	6	14
	δ-lactams C—N(—C)—C=O (endo)	1.479	1.476	0.007	1.475	1.482	15	14
	δ-lactams C—N(—C)—C=O (exo)	1.468	1.471	0.009	1.462	1.477	15	14
	nitro compounds (1,2-dinitro omitted):
	C—CH₂—NO₂	1.485	1.483	0.020	1.478	1.502	8
	C₂—CH—NO₂	1.509	1.509	0.011	1.502	1.511	12
	C₃—C—NO₂	1.533	1.533	0.013	1.530	1.539	17
	C₂—C—(NO₂)₂	1.537	1.536	0.016	1.525	1.550	19
	1,2-dinitro: NO₂—C—C—NO₂	1.552	1.550	0.023	1.536	1.572	32
Csp³—N(2)	C ^# —N=N	1.493	1.493	0.020	1.477	1.506	54
Csp³—N(2)	C* —N=C—C_ar	1.465	1.468	0.011	1.461	1.472	75
Csp²—N(3)	C=C—NH₂ Nsp² planar	1.336	1.344	0.017	1.317	1.348	10	23
	C=C—NH—C^# Nsp² planar	1.339	1.340	0.016	1.327	1.351	17	23
	C=C—N—(C^#)₂ Nsp² planar	1.355	1.358	0.014	1.341	1.363	22	23
	C=C—N—(C^#)₂ Nsp³ pyramidal	1.416	1.418	0.018	1.397	1.432	18	22
	Csp²—Nsp² (N planar) in:							23
	acyclic amides NH₂—C=O	1.325	1.323	0.009	1.318	1.331	32	14
	acyclic amides C*—NH—C=O	1.334	1.333	0.011	1.326	1.343	78	14
	acyclic amides (C*)₂—N—C=O	1.346	1.342	0.011	1.339	1.356	5	14
	β-lactams C*—NH—C=O	1.385	1.388	0.019	1.374	1.396	23	13
	γ-lactams C*—NH—C=O	1.331	1.331	0.011	1.326	1.337	20	13
	γ-lactams C—N(—C)—C=O	1.347	1.344	0.014	1.335	1.359	15	13
	δ-lactams C*—NH—C=O	1.334	1.334	0.006	1.330	1.339	6	14
	δ-lactams C—N(—C)—C=O	1.352	1.353	0.010	1.344	1.356	15	14
	peptides C^#—N(—X)—C(—C^#)(=O)	1.333	1.334	0.013	1.326	1.340	380	24
	ureas (NH₂)₂—C=O	1.334	1.334	0.008	1.329	1.339	48	25, 26
	ureas (C^#—NH)₂—C=O	1.347	1.345	0.010	1.341	1.354	26	25
	ureas [(C^#)_n—N]₂—C=O	1.363	1.359	0.014	1.354	1.370	40	25, 27
	thioureas (X₂N)₂—C=S	1.346	1.343	0.023	1.328	1.361	192
	imides [C^#—C(=O)]₂—NH	1.376	1.377	0.012	1.369	1.383	64
	imides [C^#—C(=O)]₂—N—C^#	1.389	1.383	0.017	1.376	1.404	38
	imides [Csp²—C(=O)]₂—N—C^#	1.396	1.396	0.010	1.389	1.403	46
	imides [Csp²—C(=O)]₂—N—Csp²	1.409	1.406	0.020	1.391	1.419	28
	guanidinium [C—(NH₂)₃]⁺ (unsubstituted)	1.321	1.320	0.008	1.314	1.327	39
	guanidinium [C—(NH₂)₃]⁺ (any substituent)	1.328	1.325	0.015	1.317	1.333	140
	in heterocyclic systems (any substituent):
	1H-pyrrole (N1—C2, N1—C5)	1.372	1.374	0.016	1.363	1.384	58
	indole (N1—C2)	1.370	1.370	0.012	1.364	1.377	40
	pyrazole (N1—C5)	1.357	1.359	0.012	1.347	1.365	20
	imidazole (N1—C2)	1.349	1.349	0.018	1.338	1.358	44
	imidazole (N1—C5)	1.370	1.370	0.010	1.365	1.377	44
Csp²—N(2)	in imidazole (N3—C4)	1.376	1.377	0.011	1.369	1.384	44
C_ar—N(4)	C _ar —N⁺(C,H)₃	1.465	1.466	0.007	1.461	1.470	23
C_ar—N(3)	C _ar —NH₂ (Nsp²: planar)	1.355	1.360	0.020	1.340	1.372	33	23
	C _ar —NH₂ (Nsp³: pyramidal)	1.394	1.396	0.011	1.385	1.403	25	22
	C _ar —NH₂ (overall)	1.375	1.377	0.025	1.363	1.394	98	28
	C _ar —NH—C^# (Nsp²: planar)	1.353	1.353	0.007	1.347	1.359	16	23
	C _ar —NH—C^# (Nsp³: pyramidal)	1.419	1.423	0.017	1.412	1.432	8	22
	C _ar —NH—C^# (overall)	1.380	1.364	0.032	1.353	1.412	31	28
	C _ar —N—(C^#)₂ (Nsp²: planar)	1.371	1.370	0.016	1.363	1.382	41	23
	C _ar —N—(C^#)₂ (Nsp³: pyramidal)	1.426	1.425	0.011	1.421	1.431	22	22
	C _ar —N—(C^#)₂ (overall)	1.390	1.385	0.030	1.366	1.420	69	28
	in indole (N1—C7a)	1.372	1.372	0.007	1.367	1.376	40
	C _ar —NO₂	1.468	1.469	0.014	1.460	1.476	556
C_ar—N(2)	C _ar —N=N	1.431	1.435	0.020	1.422	1.442	26
Csp²=N(3)	in furoxan (⁺N2=C3)	1.316	1.316	0.009	1.311	1.324	14
Csp²=N(2)	C_ar—C=N—C^#	1.279	1.279	0.008	1.275	1.285	75
	(C,H)₂—C=N—OH in oximes	1.281	1.280	0.013	1.273	1.288	67
	S—C=N—X	1.302	1.302	0.021	1.285	1.319	36
	in pyrazole (N2=C3)	1.329	1.331	0.014	1.315	1.339	20
	in imidazole (C2=N3)	1.313	1.314	0.011	1.307	1.319	44
	in isoxazole (N2=C3)	1.314	1.315	0.009	1.305	1.320	9
	in furazan (N2=C3, C4=N5)	1.298	1.299	0.006	1.294	1.303	12
	in furoxan (C4=N5)	1.304	1.306	0.008	1.300	1.308	14
C_ar $[\ddb]$ N(3)	C $[\ddb]$ N ⁺ —H (pyrimidinium)	1.335	1.334	0.015	1.325	1.342	30
	C $[\ddb]$ N ⁺ —C* (pyrimidinium)	1.346	1.346	0.010	1.340	1.352	64
	C $[\ddb]$ N ⁺ —O⁻ (pyrimidinium)	1.362	1.359	0.013	1.353	1.369	56
C_ar $[\ddb]$ N(2)	C $[\ddb]$ N (pyridine)	1.337	1.338	0.012	1.300	1.344	269
	C $[\ddb]$ N (pyrazine)	1.336	1.335	0.022	1.319	1.347	120
	C $[\ddb]$ N $[\ddb]$ C (pyrimidine)	1.339	1.338	0.015	1.333	1.342	28
	N $[\ddb]$ C $[\ddb]$ N (pyrimidine)	1.333	1.335	0.013	1.326	1.337	28
	C $[\ddb]$ N (pyrimidine) (overall)	1.336	1.337	0.014	1.331	1.339	56
	in any six-membered N-containing aromatic ring:
	H—C $[\ddb]$ N $[\ddb]$ C—H	1.334	1.334	0.014	1.327	1.341	146
	H—C $[\ddb]$ N $[\ddb]$ C—C*	1.339	1.341	0.013	1.336	1.345	38
	C—C $[\ddb]$ N $[\ddb]$ C—C	1.345	1.345	0.008	1.342	1.348	24
	C $[\ddb]$ N $[\ddb]$ C (overall)	1.336	1.337	0.014	1.329	1.344	204
Csp¹≡N(2)	X —N⁺≡C⁻ (isocyanide)	1.144	1.147	0.006	1.140	1.148	6
Csp¹≡N(1)	C*—C≡N	1.136	1.137	0.010	1.131	1.142	140
	C=C—C≡N in TCNQ	1.144	1.144	0.008	1.139	1.149	284	19
	C_ar—C≡N	1.138	1.138	0.007	1.133	1.143	31
	X —S—C≡N	1.144	1.141	0.012	1.138	1.151	10
	(S—C≡N)⁻	1.155	1.156	0.012	1.147	1.165	14
Csp³—O(2)	in alcohols:
	CH₃—OH	1.413	1.414	0.018	1.395	1.425	17
	C—CH₂—OH	1.426	1.426	0.011	1.420	1.431	75
	C₂—CH—OH	1.432	1.431	0.011	1.425	1.439	266
	C₃—C—OH	1.440	1.440	0.012	1.432	1.449	106
	C*—OH (overall)	1.432	1.431	0.013	1.424	1.441	464
	in dialkyl ethers:							29
	CH₃—O—C*	1.416	1.418	0.016	1.405	1.426	110
	C—CH₂—O—C*	1.426	1.424	0.011	1.418	1.435	34
	C₂—CH—O—C*	1.429	1.430	0.010	1.420	1.437	53
	C₃—C—O—C*	1.452	1.450	0.011	1.445	1.458	39
	C—O—C (overall)	1.426	1.425	0.019	1.414	1.437	236	5
	in aryl alkyl ethers:							29
	CH₃—O—C_ar	1.424	1.424	0.012	1.417	1.431	616
	C—CH₂—O—C_ar	1.431	1.430	0.013	1.422	1.438	188
	C₂—CH—O—C_ar	1.447	1.446	0.020	1.435	1.466	58
	C₃—C—O—C_ar	1.470	1.469	0.018	1.456	1.483	55
	C*—O—C_ar (overall)	1.429	1.427	0.018	1.419	1.436	917
	in alkyl esters of carboxylic acids:							12, 29
	CH₃—O—C(=O)—C*	1.448	1.449	0.010	1.442	1.455	200
	C—CH₂—O—C(=O)—C*	1.452	1.453	0.009	1.445	1.458	32
	C₂—CH—O—C(=O)—C*	1.460	1.460	0.010	1.454	1.465	78
	C₃—C—O—C(=O)—C*	1.477	1.475	0.008	1.472	1.484	6
	C—O—C(=O)—C (overall)	1.450	1.451	0.014	1.442	1.459	314
	in alkyl esters of α,β-unsaturated acids:
	C*—O—C(=O)—C=C (overall)	1.453	1.452	0.013	1.444	1.459	112
	in alkyl esters of benzoic acid:
	C*—O—C(=O)—C(phenyl) (overall)	1.454	1.454	0.012	1.446	1.463	219
	in ring systems:
	oxirane (epoxide) (any substituent)	1.446	1.446	0.014	1.438	1.456	498	9
	oxetane (any substituent)	1.463	1.460	0.015	1.451	1.474	16
	tetrahydrofuran (C,H substituents)	1.442	1.441	0.017	1.430	1.451	154
	tetrahydropyran (C,H substituents)	1.441	1.442	0.015	1.431	1.451	22
	β-lactones: C*—O—C(=O)	1.492	1.494	0.010	1.481	1.501	4	16
	γ-lactones: C*—O—C(=O)	1.464	1.464	0.012	1.455	1.473	110	12
	δ-lactones: C*—O—C(=O)	1.461	1.464	0.017	1.452	1.473	27	12
	O—C—O systems in gem-diols, and pyranose and furanose sugars:							30, 31
	HO—C*—OH	1.397	1.401	0.012	1.388	1.405	18
	C ₅ —O₅—C₁—O₁H in pyranoses:
	O₁ axial (α): C₅—O₅	1.439	1.440	0.008	1.432	1.445	29
	O₁ axial (α): O₅—C₁	1.427	1.426	0.012	1.421	1.432	29
	O₁ axial (α): C₁—O₁	1.403	1.400	0.012	1.391	1.412	29
	O₁ equatorial (β): C₅—O₅	1.435	1.436	0.008	1.429	1.440	17
	O₁ equatorial (β): O₅—C₁	1.430	1.431	0.010	1.424	1.436	17
	O₁ equatorial (β): C₁—O₁	1.393	1.393	0.007	1.386	1.399	17
	α + β (overall): C₅—O₅	1.439	1.440	0.008	1.432	1.446	60
	α + β (overall): O₅—C₁	1.430	1.429	0.012	1.421	1.436	60
	α + β (overall): C₁—O₁	1.401	1.399	0.011	1.392	1.407	60
	C ₄ —O₄—C₁—O₁H in furanoses:
	(overall values) C₄—O₄	1.442	1.446	0.012	1.436	1.449	18
	(overall values) O₄—C₁	1.432	1.432	0.012	1.421	1.443	18
	(overall values) C₁—O₁	1.404	1.405	0.013	1.397	1.409	18
	C ₅ —O₅—C₁—O₁—C* in pyranoses:
	O₁ axial (α): C₅—O₅	1.439	1.438	0.010	1.433	1.446	67
	O₁ axial (α): O₅—C₁	1.417	1.417	0.009	1.410	1.424	67
	O₁ axial (α): C₁—O₁	1.409	1.409	0.014	1.401	1.417	67
	O₁ axial (α): O₁—C*	1.435	1.435	0.013	1.427	1.443	67
	O₁ equatorial (β): C₅—O₅	1.434	1.435	0.006	1.429	1.439	39
	O₁ equatorial (β): O₅—C₁	1.424	1.424	0.008	1.418	1.431	39
	O₁ equatorial (β): C₁—O₁	1.390	1.390	0.011	1.381	1.400	39
	O₁ equatorial (β): O₁—C*	1.437	1.438	0.013	1.428	1.445	39
	α + β (overall): C₅—O₅	1.436	1.436	0.009	1.431	1.442	126
	α + β (overall): O₅—C₁	1.419	1.419	0.011	1.412	1.426	126
	α + β (overall): C₁—O₁	1.402	1.403	0.016	1.391	1.413	126
α + β (overall): O₁—C*	1.436	1.436	0.013	1.428	1.445	126
C ₄ —O₄—C₁—O₁—C* in furanoses:
(overall values) C₄—O₄	1.443	1.445	0.013	1.429	1.453	23
(overall values) O₄—C₁	1.421	1.418	0.012	1.413	1.431	23
(overall values) C₁—O₁	1.410	1.409	0.014	1.401	1.420	23
(overall values) O₁—C*	1.439	1.437	0.014	1.429	1.449	23
Miscellaneous:
C^#—O—SiX₃	1.416	1.416	0.017	1.405	1.428	29
C*—O—SO₂—C	1.465	1.461	0.014	1.454	1.475	33
Csp²—O(2)	in enols: C=C—OH	1.333	1.331	0.017	1.324	1.342	53
	in enol esters: C=C—O—C*	1.354	1.353	0.016	1.341	1.363	40
	in acids: C*—C(=O)—OH	1.308	1.311	0.019	1.298	1.320	174
	in acids: C=C—C(=O)—OH	1.293	1.295	0.019	1.279	1.307	22
	in acids: C_ar—C(=O)—OH	1.305	1.311	0.020	1.291	1.317	75
	in esters: C—C(=O)—O—C	1.336	1.337	0.014	1.328	1.346	551	12, 29
	in esters: C=C—C(=O)—O—C*	1.332	1.331	0.011	1.324	1.339	112
	in esters: C_ar—C(=O)—O—C*	1.337	1.335	0.013	1.329	1.344	219	12
	in esters: C*—C(=O)—O—C=C	1.362	1.359	0.018	1.351	1.374	26
	in esters: C*—C(=O)—O—C=C	1.407	1.405	0.017	1.394	1.420	26
	in esters: C*—C(=O)—O—C_ar	1.360	1.359	0.011	1.355	1.367	40	12
	in anhydrides: O=C—O—C=O	1.386	1.386	0.011	1.379	1.393	70
	in ring systems:
	furan (O1—C2, O1—C5)	1.368	1.369	0.015	1.359	1.377	125
	isoxazole (O1—C5)	1.354	1.354	0.010	1.345	1.360	9
	β-lactones: C—C(=O)—O—C	1.359	1.359	0.013	1.348	1.371	4	13
	γ-lactones: C—C(=O)—O—C	1.350	1.349	0.012	1.342	1.359	110	12
	δ-lactones: C—C(=O)—O—C	1.339	1.339	0.016	1.332	1.347	27	12
C_ar—O(2)	in phenols: C_ar—OH	1.362	1.364	0.015	1.353	1.373	511
	in aryl alkyl ethers: C_ar—O—C*	1.370	1.370	0.011	1.363	1.377	920	29, 32
	in diaryl ethers: C_ar—O—C_ar	1.384	1.381	0.014	1.375	1.391	132
	in esters: C_ar—O—C(=O)—C*	1.401	1.401	0.010	1.394	1.408	40	12
Csp²=O(1)	in aldehydes and ketones:
	C*—CH=O	1.192	1.912	0.005	1.188	1.197	7
	(C*)₂—C=O	1.210	1.210	0.008	1.206	1.215	474	5
	(C^#)₂—C=O in cyclobutanones	1.198	1.198	0.007	1.194	1.204	12
	(C^#)₂—C=O in cyclopentanones	1.208	1.208	0.007	1.203	1.212	155
	(C^#)₂—C=O in cyclohexanones	1.211	1.211	0.009	1.207	1.216	312
	C=C—C=O	1.222	1.222	0.010	1.216	1.229	225
	(C=C)₂—C=O	1.233	1.229	0.010	1.226	1.242	28
	C_ar—C=O	1.221	1.218	0.014	1.212	1.229	85
	(C_ar)₂—C=O	1.230	1.226	0.015	1.220	1.238	66
	C=O in benzoquinones	1.222	1.220	0.013	1.211	1.231	86
	delocalized double bonds in carboxylate anions:
	H—C $[\ddb]$ O (formate)	1.242	1.243	0.012	1.234	1.252	24
	C*—C $[\ddb]$ O	1.254	1.253	0.010	1.247	1.261	114
	C=C—C $[\ddb]$ O	1.250	1.248	0.017	1.238	1.261	52
	C_ar—C $[\ddb]$ O	1.255	1.253	0.010	1.249	1.262	22
	HOOC—C $[\ddb]$ O (hydrogen oxalate)	1.243	1.247	0.015	1.232	1.256	26
	⁻O₂ $[\ddb]$ C—C $[\ddb]$ O (oxalate)	1.251	1.251	0.007	1.248	1.254	18
	in carboxylic acids (X—COOH):
	C*—C(=O)—OH	1.214	1.214	0.019	1.203	1.224	175
	C=C—C(=O)—OH	1.229	1.226	0.017	1.218	1.237	22
	C_ar—C(=O)—OH	1.226	1.223	0.020	1.211	1.241	75
	in esters:
	C—C(=O)—O—C	1.196	1.196	0.010	1.190	1.202	551	12
	C=C—C(=O)—O—C*	1.199	1.198	0.009	1.193	1.203	113
	C_ar—C(=O)—O—C*	1.202	1.201	0.009	1.196	1.207	218	12
	C*—C(=O)—O—C=C	1.190	1.190	0.014	1.184	1.198	26
	C*—C(=O)—O—C_ar	1.187	1.188	0.011	1.181	1.195	40	12
	in anhydrides: O=C—O—C=O	1.187	1.187	0.010	1.184	1.193	70
	in β-lactones: C—C(=O)—O—C	1.193	1.193	0.006	1.187	1.198	4	13
	γ-lactones: C—C(=O)—O—C	1.201	1.202	0.009	1.196	1.206	109	12
	δ-lactones: C—C(=O)—O—C	1.205	1.207	0.008	1.201	1.209	27	12
	in amides:
	NH₂—C(—C*)=O	1.234	1.233	0.012	1.225	1.243	32	14
	(C—)(C,H—)N—C(—C*)=O	1.231	1.231	0.012	1.224	1.238	378	14
	β-lactams: C*—NH—C=O	1.198	1.200	0.012	1.193	1.204	23	13
	γ-lactams: C*—NH—C=O	1.235	1.235	0.008	1.232	1.240	20	13
	γ-lactams: C—N(—C)—C=O	1.225	1.226	0.011	1.217	1.233	15	13
	δ-lactams: C*—NH—C=O	1.240	1.241	0.003	1.237	1.243	6	14
	δ-lactams: O—N(—C)—C=O	1.233	1.233	0.007	1.229	1.239	15	14
	in ureas:
	(NH₂)₂—C=O	1.256	1.256	0.007	1.249	1.261	24	25, 26
	(C^#—NH)₂—C=O	1.241	1.237	0.011	1.235	1.245	13	25
	[(C^#)_n—N]₂—C=O	1.230	1.230	0.007	1.224	1.234	20	25, 27
Csp³—P(4)	C₃—P⁺—C*	1.800	1.802	0.015	1.790	1.812	35	33
	C₂—P(=O)—CH₃	1.791	1.790	0.006	1.786	1.795	10
	C₂—P(=O)—CH₂—C	1.806	1.806	0.009	1.801	1.813	45
	C₂—P(=O)—CH—C₂	1.821	1.821	0.009	1.815	1.828	15
	C₂—P(=O)—C—C₃	1.841	1.842	0.008	1.835	1.847	14
	C₂—P(=O)—C* (overall)	1.813	1.811	0.017	1.800	1.822	84
Csp³—P(3)	C₂—P—C*	1.855	1.857	0.019	1.840	1.870	23
C_ar—P(4)	C₃—P⁺—C_ar	1.793	1.792	0.011	1.786	1.800	276
	C₂—P(=O)—C_ar	1.801	1.802	0.011	1.796	1.807	98
	Ph ₃ —P=N⁺=P—Ph₃	1.795	1.795	0.008	1.789	1.800	197
C_ar—P(3)	C₂—P—C_ar	1.836	1.837	0.010	1.830	1.844	102
C_ar—P(3)	(N $[\ddb]$ )₂P—C_ar (P $[\ddb]$ N aromatic)	1.795	1.793	0.011	1.788	1.803	43
Csp³—S(4)	C* —SO₂—C (C* = CH₃ excluded)	1.786	1.782	0.018	1.774	1.797	75
	C* —SO₂—C (overall)	1.779	1.778	0.020	1.764	1.790	94
	C *—SO₂—O—X	1.745	1.744	0.009	1.738	1.754	7	34
	C* —SO₂—N—X₂	1.758	1.736	0.018	1.746	1.773	17	34
Csp³—S(3)	C* —S(=O)—C (C* = CH₃ excluded)	1.818	1.814	0.024	1.802	1.829	69
	C* —S(=O)—C (overall)	1.809	1.806	0.025	1.793	1.820	88
	C H₃—S⁺— $[X_{2}]$	1.786	1.787	0.007	1.779	1.792	21
	C* —S⁺—X₂ (C* = CH₃ excluded)	1.823	1.820	0.016	1.812	1.834	18
	C* —S⁺—C₂ (overall)	1.804	1.794	0.025	1.788	1.820	41
Csp³—S(2)	C *—SH	1.808	1.805	0.010	1.800	1.819	6
	C H₃—S—C*	1.789	1.787	0.008	1.784	1.794	9
	C—CH₂—S—C*	1.817	1.816	0.013	1.808	1.824	92
	C₂—CH—S—C*	1.819	1.819	0.011	1.811	1.825	32
	C₃—C—S—C*	1.856	1.860	0.011	1.854	1.863	26
	C* —S—C* (overall)	1.819	1.817	0.019	1.809	1.827	242
	in thiirane	1.834	1.835	0.025	1.810	1.858	4	9
	in thietane: see ZCMXSP (1.817, 1.844)
	in tetrahydrothiophene	1.827	1.826	0.018	1.811	1.837	20
	in tetrahydrothiopyran	1.823	1.821	0.014	1.812	1.832	24
	C—CH₂—S—S—X	1.823	1.820	0.014	1.813	1.832	41
	C₃—C—S—S—X	1.863	1.865	0.015	1.848	1.878	11
	C* —S—S—X (overall)	1.833	1.828	0.022	1.818	1.848	59
Csp²—S(2)	C=C—S—C*	1.751	1.755	0.017	1.740	1.764	61
	C=C—S—C=C (in tetrathiafulvalene)	1.741	1.741	0.011	1.733	1.750	88
	C=C—S—C=C (in thiophene)	1.712	1.712	0.013	1.703	1.722	60
	O=C—S—C^#	1.762	1.759	0.018	1.747	1.778	20
C_ar—S(4)	C _ar —SO₂—C	1.763	1.764	0.009	1.756	1.769	96
	C _ar —SO₂—O—X	1.752	1.750	0.008	1.749	1.756	27
	C _ar —SO₂—N—X₂	1.758	1.759	0.013	1.749	1.765	106	35
C_ar—S(3)	C _ar —S(=O)—C	1.790	1.790	0.010	1.783	1.798	41
C_ar—S(3)	C _ar —S⁺—X₂	1.778	1.779	0.010	1.771	1.787	10
C_ar—S(2)	C _ar —S—C*	1.773	1.774	0.009	1.765	1.779	44
	C _ar —S—C_ar	1.768	1.767	0.010	1.762	1.774	158
	C _ar —S—C_ar (in phenothiazine)	1.764	1.764	0.008	1.760	1.769	48
	C _ar —S—S—X	1.777	1.777	0.012	1.767	1.785	47
Csp¹—S(2)	N≡C—S—X	1.679	1.683	0.026	1.645	1.698	10
Csp¹—S(1)	(N≡C—S)⁻	1.630	1.630	0.014	1.619	1.641	14
Csp²=S(1)	(C*)₂—C=S: see IPMUDS (1.599)
	(C_ar)₂—C=S: see CELDOM (1.611)
	(X)₂—C=S (X = C,N,O,S)	1.671	1.675	0.024	1.656	1.689	245
	X ₂ N—C(=S)—S—X	1.660	1.660	0.016	1.648	1.674	38
	(X₂N)₂—C=S (thioureas)	1.681	1.684	0.020	1.669	1.693	96
	N—C( $[\ddb]$ S)₂	1.720	1.721	0.012	1.709	1.731	20
Csp³—Se	C ^# —Se	1.970	1.967	0.032	1.948	1.998	21
Csp²—Se(2)	C=C—Se—C=C (in tetraselenafulvalene)	1.893	1.895	0.013	1.882	1.902	32
C_ar—Se(3)	Ph ₃ —Se⁺	1.930	1.929	0.006	1.924	1.936	13
Csp³—Si(5)	C ^# —Si⁻—X₄	1.874	1.876	0.015	1.859	1.884	9
Csp³—Si(4)	C H₃—Si—X₃	1.857	1.857	0.018	1.848	1.869	552
	C* —Si—X₃ (C* = CH₃ excluded)	1.888	1.887	0.023	1.872	1.905	124
	C* —Si—X₂ (overall)	1.863	1.861	0.024	1.850	1.875	681
C_ar—Si(4)	C _ar —Si—X₃	1.868	1.868	0.014	1.857	1.878	178
Csp¹—Si(4)	C≡C—Si—X₃	1.837	1.840	0.012	1.824	1.849	8
Csp³—Te	C ^# —Te	2.158	2.159	0.030	2.128	2.177	13
C_ar—Te	C _ar —Te	2.116	2.115	0.020	2.104	2.130	72
Csp²=Te	see CEDCUJ (2.044)
Cl—Cl	see PHASCL (2.306, 2.227)
Cl—I	see CMBIDZ (2.563), HXPASC (2.541, 2.513), METAMM (2.552), BQUINI (2.416, 2.718)
Cl—N	see BECTAE (1.743–1.757), BOGPOC (1.705)
Cl—O(1)	in ClO	1.414	1.419	0.026	1.403	1.431	252
Cl—P	(N $[\ddb]$ )₂P—Cl (N $[\ddb]$ P aromatic)	1.997	1.994	0.015	1.989	2.004	46
Cl—P	Cl —P (overall)	2.008	2.001	0.035	1.986	2.028	111
Cl—S	Cl —S (overall)	2.072	1.079	0.023	2.047	2.091	6
Cl—S	see also longer bonds in CILSAR (2.283), BIHXIZ (2.357), CANLUY (2.749)
Cl—Se	See BIRGUE10, BIRHAL10, CTCNSE (2.234–2.851)
Cl—Si(4)	Cl —Si—X₃ (monochloro)	2.072	2.075	0.009	2.066	2.078	5
Cl—Si(4)	Cl ₂ —Si—X₂ and Cl₃—Si—X	2.020	2.012	0.015	2.007	2.036	5
Cl—Te	Cl—Te in range 2.34–2.60	2.520	2.515	0.034	2.493	2.537	22	36
Cl—Te	see also longer bonds in BARRIV, BOJPUL, CETUTE, EPHTEA, OPNTEC10 (2.73–2.94)
F—N(3)	F —N—C₂ and F₂—N—C	1.406	1.404	0.016	1.395	1.416	9
F—P(6)	in hexafluorophosphate, PF	1.579	1.587	0.025	1.563	1.598	72
P—P(3)	(N $[\ddb]$ )₂P—F (N $[\ddb]$ P aromatic)	1.495	1.497	0.016	1.481	1.510	10
F—S	43 observations in range 1.409–1.770 in a wide variety of environments
	F —S(6) in F₂—SO₂—C₂ (see FPSULF10, BETJOZ)	1.640	1.646	0.011	1.626	1.649	6
	F —S(4) in F₂—S(=O)—N (see BUDTEZ)	1.527	1.528	0.004	1.524	1.530	24	37
F—Si(6)	in SiF $[^{2-}_6]$	1.694	1.701	0.013	1.677	1.703	6
F—Si(5)	F —Si⁻—X₄	1.636	1.639	0.035	1.602	1.657	10
F—Si(4)	F —Si—X₃	1.588	1.587	0.014	1.581	1.599	24
F—Te	see CUCPIZ [F—Te(6) = 1.942, 1.937], FPHTEL [F—Te(4) = 2.006]
H—N(4)	X ₃ —N⁺—H	1.033	1.036	0.022	1.026	1.045	87	21
H—N(3)	X ₂ —N—H	1.009	1.010	0.019	0.997	1.023	95	21
H—O(2)	in alcohols C*—O—H	0.967	0.969	0.010	0.959	0.974	63	21
	in alcohols C^#—O—H	0.967	0.970	0.010	0.959	0.974	73	21
	in acids O=C—O—H	1.015	1.017	0.017	1.001	1.031	16	21, 38
I—I	in $[{\rm I}^-_3]$	2.917	2.918	0.011	2.907	2.927	6
I—N	see BZPRIB, CMBIDZ, HMTITI, HMTNTI, IFORAM, IODMAM (2.042–2.475)
I—O	X —I—O (see BZPRIB, CAJMAB, IBZDAC11) for IO see BOVMEE (1.829–1.912)	2.144	2.144	0.028	2.127	2.164	6
I—P(3)	see CEHKAB (2.490–2.493)							^‡
I—S	see DTHIBR10 (2.687), ISUREA10 (2.629), BZTPPI (3.251)
I—Te(4)	I —Te—X₃	2.926	2.928	0.026	2.902	2.944	8
N(4)—N(3)	X ₃ —N⁺—N⁰—X₂ (N⁰ planar)	1.414	1.414	0.005	1.412	1.418	13
N(3)—N(3)	(C)(C,H)—N_a—N_b—(C)(C,H)							5, 39
	N_a, N_b pyramidal	1.454	1.452	0.021	1.444	1.457	44	40
	N_a pyramidal, N_b planar	1.420	1.420	0.015	1.407	1.433	68	40
	N_a, N_b planar	1.401	1.401	0.018	1.384	1.418	40	40
	overall	1.425	1.425	0.027	1.407	1.443	139
N(3)—N(2)	in pyrazole (N1—N2)	1.366	1.366	0.019	1.350	1.375	20
N(3)—N(2)	in pyridazinium (N1⁺ $[\ddb]$ N2)	1.350	1.349	0.010	1.345	1.361	7
N(2) $[\ddb]$ N(2)	N $[\ddb]$ N (aromatic) in pyridazine
	with C,H as ortho substituents	1.304	1.300	0.019	1.287	1.326	6
	with N,Cl as ortho substituents	1.368	1.373	0.011	1.362	1.375	9
N(2)=N(2)	C^#—N=N—C^# (cis)	1.245	1.244	0.009	1.239	1.252	21
	C^#—N=N—C^# (trans)	1.222	1.222	0.006	1.218	1.227	6
	C^#—N=N—C^# (overall)	1.240	1.241	0.012	1.230	1.251	27
	C_ar—N=N—C_ar	1.255	1.253	0.016	1.247	1.262	13
	X —N=N=N (azides)	1.216	1.226	0.028	1.202	1.237	19
N(2)=N(1)	X —N=N=N (azides)	1.124	1.128	0.015	1.114	1.137	19
N(3)—O(2)	(C,H)₂—N—OH (Nsp²: planar)	1.396	1.394	0.012	1.390	1.401	28
	C₂—N—O—C (Nsp³: pyramidal)	1.463	1.465	0.012	1.457	1.468	22
	C₂—N—O—C (Nsp²: planar)	1.397	1.394	0.011	1.388	1.409	12
	in furoxan (N2—O1)	1.438	1.436	0.009	1.430	1.447	14
N(3)—O(1)	(C $[\ddb]$ )₂N⁺—O⁻ in pyridine N-oxides	1.304	1.299	0.015	1.291	1.316	11
N(3)—O(1)	in furoxan (⁺N2—O6⁻)	1.234	1.234	0.008	1.228	1.240	14
N(2)—O(2)	in oximes:
	(C^#)₂—C=N—OH	1.416	1.418	0.006	1.416	1.420	7
	(H)(Csp²)—C=N—OH	1.390	1.390	0.011	1.380	1.401	20
	(C^#)(Csp²)—C=N—OH	1.402	1.403	0.010	1.393	1.410	18
	(Csp²)₂—C=N—OH	1.378	1.377	0.017	1.365	1.393	16
	(C,H)₂—C=N—OH (overall)	1.394	1.395	0.018	1.379	1.408	67
	in furazan (O1—N2, O1—N5)	1.385	1.383	0.013	1.378	1.392	12
	in furoxan (O1—N5)	1.380	1.380	0.011	1.370	1.388	14
	in isoxazole (O1—N2)	1.425	1.425	0.010	1.417	1.434	9
N(3)=O(1)	in nitrate ions NO	1.239	1.240	0.020	1.227	1.251	105
	in nitro groups:
	C*—NO₂	1.212	1.214	0.012	1.206	1.221	84
	C^#—NO₂	1.210	1.210	0.011	1.203	1.218	251
	C_ar—NO₂	1.217	1.218	0.011	1.211	1.215	1116
	C—NO₂ (overall)	1.218	1.219	0.013	1.210	1.226	1733
N(3)—P(4)	X ₂ —P(=X)—NX₂ Nsp²: planar	1.652	1.651	0.024	1.634	1.670	205
	X ₂ —P(=X)—NX₂ Nsp³: pyramidal	1.683	1.683	0.005	1.680	1.686	6
	X ₂ —P(=X)—NX₂ (overall)	1.662	1.662	0.029	1.639	1.682	358
	subsets of this group are:
	O₂—P(=S)—NX₂	1.628	1.624	0.015	1.615	1.634	9
	C—P(=S)—(NX₂)₂	1.691	1.694	0.018	1.678	1.703	28
	O—P(=S)—(NX₂)₂	1.652	1.654	0.014	1.642	1.664	28
	P(=O)—(NX₂)₃	1.663	1.668	0.026	1.640	1.679	78
N(3)—P(3)	—NX—P(—X)—NX—P(—X)— (P₂N₂ ring)	1.730	1.721	0.017	1.716	1.748	20
	—NX—P(=S)—NX—P(=S)— (P₂N₂ ring)	1.697	1.697	0.015	1.690	1.703	44
	in P-substituted phosphazenes:
	(N $[\ddb]$ )₂P—N (amino)	1.637	1.638	0.014	1.625	1.651	16
	(N $[\ddb]$ )₂P—N (aziridinyl)	1.672	1.674	0.010	1.665	1.676	15
N(2)=P(4)	Ph₃—P=N⁺=P—Ph₃	1.571	1.573	0.013	1.563	1.580	66
N(2)=P(4)	Ph₃—P=N—C,S	1.599	1.597	0.018	1.580	1.615	7
N(2) $[\ddb]$ P(3)	N $[\ddb]$ P aromatic in phosphazenes	1.582	1.582	0.019	1.571	1.594	126
N(2) $[\ddb]$ P(3)	N $[\ddb]$ P aromatic in P $[\ddb]$ N $[\ddb]$ S	1.604	1.606	0.009	1.594	1.612	36
N(3)—S(4)	C—SO₂—NH₂	1.600	1.601	0.012	1.591	1.610	14	35
	C—SO₂—NH—C^#	1.633	1.633	0.019	1.615	1.652	47	35
	C—SO₂—N—(C^#)₂	1.642	1.641	0.024	1.623	1.659	38	35
N(3)—S(2)	C—S—NX₂ Nsp²: planar	1.710	1.707	0.019	1.698	1.722	22	23
	(for Nsp³ pyramidal see MODIAZ: 1.765)
	X —S—NX₂ Nsp²: planar	1.707	1.705	0.012	1.699	1.715	30	23
N(2)—S(2)	C=N—S—X	1.656	1.663	0.027	1.632	1.677	36
N(2) $[\ddb]$ S(2)	N $[\ddb]$ S aromatic in P $[\ddb]$ N $[\ddb]$ S	1.560	1.558	0.011	1.554	1.563	37
N(2)=S(2)	N =S in N=S=N and N=S=S	1.541	1.546	0.022	1.521	1.558	37
N(3)—Se	see COJCUZ (1.830), DSEMOR10 (1.846, 1.852), MORTRS10 (1.841)
N(2)—Se	see SEBZQI (1.805), NAPSEZ10 (1.809, 1.820)
N(2)=Se	see CISMUM (1.790, 1.791)
N(3)—Si(5)	see DMESIP01, BOJLER, CASSAQ, CASYOK, CECXEN, CINTEY, CIPBUY, FMESIB, MNPSIL, PNPOSI (1.973–2.344)
N(3)—Si(4)	X ₃ —Si—NX₂ (overall)	1.748	1.746	0.022	1.735	1.757	170
	subsets of this group are:
	X₃—Si—NHX	1.714	1.719	0.014	1.702	1.727	16
	X₃—Si—NX—Si—X₃ acyclic	1.743	1.744	0.016	1.731	1.755	45
	N—Si—N in four-membered rings	1.742	1.742	0.009	1.735	1.748	53
	N—Si—N in five-membered rings	1.741	1.742	0.019	1.726	1.749	33
N(2)—Si(4)	X ₃ —Si—N⁻—Si—X₃	1.711	1.712	0.019	1.693	1.729	15
N—Te	see ACLTEP (2.402), BIBLAZ (1.980), CESSAU (2.023)
O(2)—O(2)	C—O—O—C,H τ(OO) = 70–85°	1.464	1.464	0.009	1.458	1.472	12
	C—O—O—C,H τ(OO) approx. 180°	1.482	1.480	0.005	1.478	1.486	5
	C—O—O—C,H (overall)	1.469	1.471	0.012	1.461	1.478	17
	O=C—O—O—C=O see ACBZPO01 (1.446), CEYLUN (1.452), CIMHIP (1.454)
	Si—O—O—Si	1.496	1.499	0.005	1.490	1.499	10
O(2)—P(5)	X —P—(OX)₄							41
	trigonal bipyramidal: axial	1.689	1.685	0.024	1.675	1.712	20
	trigonal bipyramidal: equatorial	1.619	1.622	0.024	1.604	1.628	20
	square pyramidal	1.662	1.661	0.020	1.649	1.673	28
O(2)—P(4)	C—O—P( $[\ddb]$ O) $[^{2-}_3]$	1.621	1.622	0.007	1.615	1.628	12
	(H—O)₂—P( $[\ddb]$ O)	1.560	1.561	0.009	1.555	1.566	16
	(C—O)₂—P( $[\ddb]$ O)	1.608	1.607	0.013	1.599	1.615	16
	(C^#—O)₃—P=O	1.558	1.554	0.011	1.550	1.564	30
	(C_ar—O)₃—P=O	1.587	1.588	0.014	1.572	1.599	19
	X —O—P(=O)—(C,N)₂	1.590	1.585	0.016	1.577	1.601	33
	(X—O)₂—P(=O)—(C,N)	1.571	1.572	0.013	1.563	1.579	70
O(2)—P(3)	(N $[\ddb]$ )₂P—O—C (N $[\ddb]$ P aromatic)	1.573	1.573	0.011	1.563	1.584	16
O(1)=P(4)	C—O—P( $[\ddb]$ O) $[^{2-}_3]$ (delocalized)	1.513	1.512	0.008	1.508	1.518	42
	(H—O)₂—P( $[\ddb]$ O) (delocalized)	1.503	1.503	0.005	1.499	1.508	16
	(C—O)₂—P( $[\ddb]$ O) (delocalized)	1.483	1.485	0.008	1.474	1.490	16
	(C—O)₃—P=O	1.449	1.448	0.007	1.446	1.452	18
	C₃—P=O	1.489	1.486	0.010	1.481	1.496	72
	N₃—P=O	1.461	1.462	0.014	1.449	1.470	26
	(C)₂(N)—P=O	1.487	1.489	0.007	1.479	1.493	5
	(C,N)₂(O)—P=O	1.467	1.465	0.007	1.462	1.472	33
	(C,N)(O)₂—P=O	1.457	1.458	0.009	1.454	1.462	35
O(2)—S(4)	C—O—SO₂—C	1.577	1.576	0.015	1.566	1.584	41
	C—O—SO₂—CH₃	1.569	1.569	0.013	1.556	1.582	7
	C—O—SO₂—C_ar	1.580	1.578	0.015	1.571	1.588	27
O(1)=S(4)	C—SO₂—C	1.436	1.437	0.010	1.431	1.442	316	42
	X —SO₂—NX₂	1.428	1.428	0.010	1.422	1.434	326
	C—SO₂—N—(C,H)₂	1.430	1.430	0.009	1.425	1.435	206
	C—SO₂—O—C	1.423	1.423	0.008	1.418	1.428	82
	in SO $[^{2-}_4]$	1.472	1.473	0.013	1.463	1.481	104
O(1)=S(3)	C—S(=O)—C	1.497	1.498	0.013	1.489	1.505	90	5
O—Se	see BAPPAJ, BIRGUE10, BIRHAL10, CXMSEO, DGLYSE, SPSEBU
O—Se	(1.597 for O=Se to 1.974 for O—Se)
O(2)—Si(5)	(X—O)₃—Si—(N)(C)	1.663	1.658	0.023	1.650	1.665	21
O(2)—Si(4)	X ₃ —Si—O—X (overall)	1.631	1.630	0.022	1.617	1.646	191
	subsets of this group are:
	X₃—Si—O—C^#	1.645	1.647	0.012	1.634	1.652	29
	X₃—Si—O—Si—X₃	1.622	1.625	0.014	1.614	1.631	70
	X₃—Si—O—O—Si—X₃	1.680	1.676	0.008	1.673	1.688	10
O(2)—Te(6)	(X—O)₆—Te	1.927	1.927	0.020	1.908	1.942	16
O(2)—Te(4)	(X—O)₂—Te—X₂	2.133	2.136	0.054	2.078	2.177	12
P(4)—P(4)	X ₃ —P—P—X₃	2.256	2.259	0.025	2.243	2.277	6
P(4)—P(3)	see CECHEX (2.197), COZPIQ (2.249)
P(3)—P(3)	X ₂ —P—P—X₂	2.214	2.210	0.022	2.200	2.224	41
P(4)=P(4)	see BUTSUE (2.054)
P(3)=P(3)	see BALXOB (2.034)
P(4)=S(1)	C₃—P=S	1.954	1.952	0.005	1.950	1.957	13
	(N,O)₂(C)—P=S	1.922	1.924	0.014	1.913	1.927	26
	(N,O)₃—P=S	1.913	1.914	0.014	1.906	1.921	50
P(4)=Se(1)	X ₃ —P=Se	2.093	2.099	0.019	2.075	2.108	12
P(3)—Si(4)	X ₂ —P—Si—X₃: 3- and 4-rings excluded	2.264	2.260	0.019	2.249	2.283	22
P(3)—Si(4)	(see BOPFER, BOPFIV, CASTOF10, COZVIW: 2.201–2.317)
P(4)=Te(1)	see MOPHTE (2.356), TTEBPZ (2.327)
S(2)—S(2)	C—S—S—C τ (SS) = 75–105°	2.031	2.029	0.015	2.021	2.038	46
	C—S—S—C τ (SS) = 0–20°	2.070	2.068	0.022	2.057	2.077	28
	C—S—S—C (overall)	2.048	2.045	0.026	2.028	2.068	99
	in polysulfide chain —S—S—S—	2.051	2.050	0.022	2.037	2.065	126
S(2)—S(1)	X —N=S—S	1.897	1.896	0.012	1.887	1.908	5
S—Se(4)	see BUWZUO (2.264, 2.269)
S—Se(2)	X —Se—S (any)	2.193	2.195	0.015	2.174	2.207	9
S(2)—Si(4)	X ₃ —Si—S—X	2.145	2.138	0.020	2.130	2.158	19
S(2)—Te	X —S—Te (any)	2.405	2.406	0.022	2.383	2.424	10
S(2)—Te	X =S—Te (any)	2.682	2.686	0.035	2.673	2.694	28
Se(2)—Se(2)	X —Se—Se—X	2.340	2.340	0.024	2.315	2.361	15
Se(2)—Te(2)	see BAWFUA, BAWGAH (2.524–2.561)							^‡
Si(4)—Si(4)	X ₃ —Si—Si—X₃ three-membered rings excluded: see CIHRAM (2.511)	2.359	2.359	0.012	2.349	2.366	42
Te—Te	see CAHJOK (2.751, 2.704)

^† For numbered footnotes, see Appendix 9.5.1

.
^‡See opening paragraph of Section 9.5.3

9.5.2. Methodology

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9.5.2.1. Selection of crystallographic data

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All results given in Table 9.5.1.1 are based on X-ray and neutron diffraction results retrieved from the September 1985 version of the CSD. Neutron diffraction data only were used to derive mean bond lengths involving H atoms. This version of the CSD contained results for 49 854 single-crystal diffraction studies of organo-carbon compounds; 10 324 of these satisfied the acceptance criteria listed below and were used in the averaging procedures:

(i) Structure is `organic', i.e. belongs to the CSD chemical classes 1–65 or 70 (Cambridge Crystallographic Data Centre User Manual, 1978 ).
(ii) Atomic coordinates for the structure have been published and are available in the CSD.
(iii) Structure was determined from diffractometer data.
(iv) Structure does not contain unresolved numeric data errors from the original publication (such errors are usually typographical and are normally resolved by consultation with the authors).
(v) Structure was not reported to be disordered.
(vi) Only structures of higher precision were included on the basis of either (a) the crystallographic R factor was $[\le]$ 0.07 and the reported mean estimated standard deviation (e.s.d.) of the C—C bond lengths was $[\le]$ 0.010 Å (corresponds to AS flag = 1 or 2 in the CSD), or (b) the crystallographic R factor $[\le]$ 0.05 and the mean e.s.d. for C—C bonds was not available in the database (AS = 0 in the CSD).
(vii) Where the structure of a given compound had been determined more than once within the limits of (i)–(vi), then only the most precise determination was used.

9.5.2.2. Program system

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All calculations were performed on the University of Cambridge IBM 3081 D using the programs BIBSER, CONNSER, RETRIEVE, GEOM78, and PLUTO78 (Allen et al., 1979 ). A stand-alone program was written to implement the selection criteria, whilst a new program (STATS) was written to perform the statistical calculations described below. It was also necessary to modify CONNSER to improve the precision with which it locates chemical substructures. In particular, the program was altered to permit the location of atoms with specified coordination numbers. This was essential in the case of carbon so that atoms with coordination numbers 2, 3 and 4 (equivalent to formal hybridization states sp¹, sp², sp³) could be distinguished easily and reliably. Considerable care was taken to ensure that the correct molecular fragment was located by GEOM78 in the generation of geometrical tabulations. This often involved the explicit specification of H atoms in fragments, and the extensive use of geometrical tests on valence and torsion angles. Considerable use was also made of chemical structural diagrams, which are available in the Cambridge in-house version of the CSD for some 81% of all entries. Chemical diagrams proved useful, for example, in identifying the various coordination environments commonly adopted by atoms such as As, B, P, etc.

9.5.2.3. Classification of bonds

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The classification of bonds used in Table 9.5.1.1 is based on common functional groups, rings and ring systems, coordination spheres, etc. It is designed: (i) to appear logical, useful and reasonably self-explanatory to chemists, crystallographers, and others who may use the table; (ii) to permit a meaningful average value to be cited for each bond length. With reference to (ii), it was considered that a sample of bond lengths could be averaged meaningfully if: (a) the sample was unimodally distributed; (b) the sample standard deviation (σ) was reasonably small, ideally less than ca 0.02 Å; (c) there were no conspicuous outlying observations – those that occurred at > 4σ from the mean were automatically eliminated from the sample by STATS, other outliers were inspected carefully; (d) there were no compelling chemical reasons for further subdivision of the sample.

9.5.2.4. Statistics

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Where there are less than four independent observations of a given bond length, then each individual observation is given explicitly in the table. In all other cases, the following statistics were generated by the program STATS.

(i) The unweighted sample mean, d, where $[d=\textstyle\sum\limits^n_{i=1}d_i/n]$ and is the ith observation of the bond length in a total sample of n observations. Recent work (Taylor & Kennard, 1983 , 1985 , 1986 ) has shown that the unweighted mean is an acceptable (even preferable) alternative to the weighted mean, where the ith observation is assigned a weight equal to $[1/\sigma^2(d_i)]$ . This is especially true (Taylor & Kennard, 1985 ) where structures have been pre-screened on the basis of precision.
(ii) The sample median, m. This has the property that half of the observations in the sample exceed m, and half fall short of it.
(iii) The sample standard deviation, denoted here as σ, where: $[\sigma=\textstyle\sum\limits^n_{i=1}\, [(d_i-d)^2/(n-1)]^{1/2}.]$
(iv) The lower quartile for the sample, . This has the property that 25% of the observations are less than and 75% exceed it.
(v) The upper quartile for the sample, . This has the property that 25% of the observations exceed , and 75% fall short of it.
(vi) The number (n) of observations in the sample.

The statistics given in the final table correspond to distributions for which the automatic 4σ cut-off (see above) had been applied, and any manual removal of additional outliers (an infrequent operation) has been performed. In practice, a very small percentage of observations was excluded by these methods. The major effect of removing outliers is to improve the sample standard deviation, as shown in Fig. 9.5.2.1 in which a single observation is deleted.

Figure 9.5.2.1| top | pdf |

Effect of the removal of outliers (contributors that are > 4σ from the mean) for the C—C bond in C_ar—C≡N fragments. Relevant statistics (see text) are: $[\matrix{ & d & m & \sigma &q_l & q_u & n\cr(a)\hbox{ before}\hfill & 1.445 & 1.444 & 0.012 & 1.436 & 1.448 & 32\cr (b)\hbox{ after} \hfill & 1.455 & 1.444 & 0.008 & 1.436 & 1.448 & 31.}]$

The statistics chosen for tabulation effectively describe the distribution of bond lengths in each case. For a symmetrical, normal distribution: the mean (d) will be approximately equal to the median (m); the lower and upper quartiles [(q_l,q_u)] will be approximately symmetric about the median: $[m-q_l\simeq q_u-m]$ , and 95% of the observations may be expected to lie within ±2σ of the mean value. For a skewed distribution, d and m may differ appreciably and [q_l] and [q_u] will be asymmetric with respect to m. When a bond-length distribution is negatively skewed as in Fig. 9.5.2.2 ,i.e. very short values are more common than very long values, then it may be due to thermal-motion effects; the distances used to prepare the table were not corrected for thermal libration.

Figure 9.5.2.2| top | pdf |

Skewed distribution of B—F bond lengths in $[{\rm BF}_{4}^{-}]$ ions: d = 1.365, m = 1.372, σ = 0.029, q_l = 1.352, q_u = 1.390 for 84 observations. Note that d ≠ m and that q_l, q_u are asymmetrically disposed about the mean d.

In a number of cases, the initial bond-length distribution was clearly bimodal, as in Fig. 9.5.2.3(a). All cases of bimodality were resolved on chemical grounds before inclusion in the table, on the basis of hybridization, conformation-dependent conjugation interactions, etc. For example, the histogram of Fig. 9.5.2.3(a) was resolved into the two discrete unimodal distributions of Figs. 9.5.2.3(b), (c), which correspond to planar N(sp²), pyramidal N(sp³), respectively. The mean valence angle at N was used as the discriminator, with a range of 108–114° for Nsp³ and $[\ge]$ 117.5° for Nsp².

Figure 9.5.2.3| top | pdf |

Resolution of the bimodal distribution of C—N bond lengths in C_ar —N(Csp³)₂ fragments: (a) complete distribution; (b) distribution for planar N, mean valence angle at N > 117.6°; (c) distribution for pyramidal N, mean valence angle at N in the range 108–114°.

9.5.3. Content and arrangement of the table

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The upper triangular matrix of Fig. 9.5.3.1(a) shows the 120 possible element-pair combinations that can be formed from the 15 elements As, B, Br, C, Cl, F, H, I, N, O, P, S, Se, Si, Te. Fig. 9.5.3.1(a) contains the number of discrete average bond lengths given in the table for each element pair. 682 average values are cited for 65 element pairs, of which 511 (75%) involve carbon. Bond-length values from individual structures are given for a further 30 element pairs indicated by an asterisk in Fig. 9.5.3.1(a). Individual structures are identified by their CSD reference code (e.g. BOGSUL), and short-form literature references, ordered alphabetically by reference code, are given in Appendix 9.5.2 . For eight element pairs, the acceptance criterion (vi) was relaxed to include all available structures, irrespective of precision. These entries are denoted by a dagger in the table. No bonds were found for 25 element pairs within the subset of CSD used in this study.

Figure 9.5.3.1| top | pdf |

(a) Distribution of mean bond-length values reported in the table by element pair. An asterisk indicates a bonded pair represented by less than four contributors in the original data set. A `+' indicates bonded pairs located when restrictions on R factor and reported e.s.d. limits were lifted (see text). (b) Distribution of mean bond-length values reported in the table for C—C, C—O, C—N.

Each entry in Table 9.5.1.1 contains nine columns, of which six record the statistics of the bond-length distribution described above. The content of the remaining three columns: `Bond', `Structure', `Note', are now described.

9.5.3.1. Ordering of entries: the `Bond' column

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For an element pair X—Y, the primary ordering is alphabetic by element symbols according to the rows of Fig. 9.5.3.1(a); i.e. X changes slowest, Y fastest. The complete sequence runs from As—As to Te—Te with bonds involving carbon in the natural position: As—C $[\ldots]$ C—C $[\ldots]$ C—Te. Within a given X—Y pair, a secondary ordering is based on the coordination numbers (j) of X and Y, and on the nature of the bond between them. The bond definition is of the form X(j)—Y(j), with j decreasing fastest for Y, slowest for X, and with all single bonds preceding any multiple bonds. For carbon, the formal hybridization state replaces (but is equivalent to) the coordination number and it is for this element that the ordering rules are most clearly required. The ordering of the most populous C—C, C—N, C—O sections is illustrated in Fig. 9.5.3.1(b). The 13 possible C—C combinations follow the sequence Csp³—Csp³, Csp³—Csp², Csp³—C_ar, Csp³—Csp¹, Csp²—Csp², Csp²—C_ar, Csp²—Csp¹, C_ar—C_ar, C_ar—Csp¹, Csp¹—Csp¹, Csp²=Csp², C_ar $[\ddb]$ C_ar, Csp¹≡Csp¹. The symbol C_ar represents aryl carbon in six-membered rings, which is treated separately from Csp² throughout the table. The symbol $[\ddb]$ is used to indicate a delocalized double or aromatic bond according to context.

9.5.3.2. Definition of `Substructure'

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The chemical environment of each bond is normally defined by a linear formulation of the substructure. The target bond is set in bold type, e.g. C_ar—C≡N (aryl cyanides); C—CH₂—O—C_ar (primary alkyl aryl ethers); (C—O)₂ —P( $[\ddb]$ O)₂ (phosphate diesters). Occasionally, the chemical name of a functional group or ring system is used to define bond environment, e.g. in naphthalene, C2—C3; in imidazole, N1—C2. To avoid any possible ambiguity in these cases, we include numbered chemical diagrams in Fig. 9.5.3.2 . A combination of chemical name and linear formulation is often employed to increase the precision of the definition, e.g. NH₂—C=O in acyclic amides; C=C—C(=O)—C=O in benzoquinone. Finally, for very simple ions, the accepted conventional representation is deemed to be sufficient, e.g. in $[{\rm NO}^{-}_3]$ , $[{\rm SO}^{2-}_4]$ , etc.

Figure 9.5.3.2| top | pdf |

Alphabetized index of ring systems referred to in the table; the numbering scheme used in assembling the bond-length data is given where necessary.

The chemical definition of substructure may be followed by brief qualifying information, concerning substitution, conformational restrictions, etc. For example: Csp³—Csp³: in cyclobutane (any substituent); X—C—F₃ (X = C, H, N, O); C_ar—NH—Csp³ (Nsp³: pyramidal). Where the generic symbol X is unqualified, it denotes any element type, including hydrogen. If the qualifying information is too extensive, then it will be given as a table footnote (see below).

The `Substructure' column is designed to convey as much unambiguous information as possible within a small space. For Csp³, we have employed the short forms C* and C^#. C* indicates Csp³ whose bonds, additional to those specified in the linear formulation, are to C or H atoms only. C*—OH would then represent the group of alcohols CH₃—OH, —C—CH₂—OH, —C₂—CH—OH and —C₃—C—OH. C* is frequently used to restrict the secondary environment of a given bond to avoid the perturbing influence of, e.g., electronegative substituents. The symbol C^# is merely a space-saving device to indicate any Csp³ atom and includes C* as a subset.

9.5.3.3. Use of the `Note' column

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The `Note' column refers to the footnotes collected in Appendix 9.5.1 . These record additional information as follows: (a) additional details concerning the chemical definition of substructures, e.g. the omission of three- and four-membered rings; (b) statements of geometrical constraints used in obtaining the cited average, e.g. definition of planarity or pyramidality at N, torsional constraints in conjugated systems; (c) any peculiarities of a particular bond-length distribution, e.g. sample dominated by C* = methyl; (d) references to previously published surveys of crystallographic results relevant to the substructure in question. We do not claim that these references are in any way comprehensive and we would be grateful to authors for notification (to FHA) of any omissions. This will serve to improve the content of any future version of the table.

9.5.4. Discussion

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It should be remembered that this table has been derived from the organic section of CSD. We are aware that a number of organic bond types which occur very frequently in organometallics and metal complexes (e.g. C $[\ddb]$ C in cyclopentadienyl, C—P in triphenylphosphine, etc.) are either absent or poorly represented in this work. These omissions are rectified in Chapter 9.6 . We also note that certain bond types listed here (e.g. As—O, Si—O, Si—N, etc.) will occur with greater frequency in inorganic compounds. The interested reader is referred to the Inorganic Crystal Structure Database (Bergerhoff, Hundt, Sievers & Brown, 1983 ) for a machine-readable compendium of more relevant structural data.

The tabulation given here represents the first stage in a major project designed to obtain the average geometries of function groups, rigid rings, and the low-energy conformations of flexible rings. Details of mean bond lengths, valence angles, and conformational preferences in a wide range of substructures will form the basis of a machine-readable `fragment library' for use in molecular modelling and other areas of research. The systematic survey will be extended to derive information about distances, angles, directionality, and environmental dependence of hydrogen bonds and non-bonded interactions.

Appendix A9.5.1

A9.5.1. Notes to Table 9.5.1.1

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(1) Sample dominated by B—CH₃. For longer bonds in B⁻—CH₃, see LITMEB10 [B(4)—CH₃ = 1.621–1.644 Å].
(2) p(π)—p(π) bonding with Bsp² and Nsp² coplanar (τBN = 0 ± 15°) predominates. See G. Schmidt, R. Boese & D. Bläser [Z. Naturforsch. Teil B (1982), 37, 1230–1233].
(3) 84 observations range from 1.38 to 1.62 Å and individual values depend on substituents on B and O. For a discussion of borinic acid adducts, see S. J. Rettig & J. Trotter [Can. J. Chem. (1982), 60, 2957–2964].
(4) See M. Kaftory (1983). [In The chemistry of functional groups. Supplement D: The chemistry of halides, pseudohalides and azides, Part 2, Chap. 24, edited by S. Patai & Z. Rappoport. New York: John Wiley.]
(5) Bonds that are endocyclic or exocyclic to any three- or four-membered rings have been omitted from all averages in this section.
(6) The overall average given here is for Csp³—Csp³ bonds which carry only C or H substituents. The value cited reflects the relative abundance of each `substitution' group. The `mean of means' for the nine subgroups is 1.538 (σ = 0.022) Å.
(7) See (a) F. H. Allen [Acta Cryst. (1980), B36, 81–96] and (b) F. H. Allen [Acta Cryst. (1981), B37, 890–900].
(8) See F. H. Allen [Acta Cryst. (1984), B40, 64–72].
(9) See F. H. Allen [Tetrahedron (1982), 38, 2843–2853].
(10) See F. H. Allen [Tetrahedron (1982), 38, 645–655].
(11) Cyclopropanones and cyclobutanones excluded.
(12) See W. B. Schweizer & J. D. Dunitz [Helv. Chim. Acta (1982), 65, 1547–1554].
(13) See L. Norskov-Lauritsen, H.-B. Bürgi, P. Hoffmann & H. R. Schmidt [Helv. Chim. Acta (1985), 68, 76–82].
(14) See P. Chakrabarti & J. D. Dunitz [Helv. Chim. Acta (1982), 65, 1555–1562].
(15) See J. L. Hencher (1978). [In The chemistry of the C≡C triple bond, Chap. 2, edited by S. Patai. New York: John Wiley.]
(16) Conjugated: torsion angles about central C—C single bond is 0 ± 20° (cis) or 180 ± 20° (trans).
(17) Unconjugated: torsion angle about central C—C single bond is 20–160°.
(18) Other conjugative substituents excluded.
(19) TCNQ is tetracyanoquinodimethane (see diagrams).
(20) No difference detected between C2 $[\ddb]$ C3 and C3 $[\ddb]$ C4 bonds.
(21) Derived from neutron diffraction results only.
(22) Nsp³: pyramidal; mean valence angle at N is in the range 108–114°.
(23) Nsp²: planar; mean valence angle at N is ≥ 117.5°.
(24) Cyclic and acyclic peptides.
(25) See R. H. Blessing [J. Am. Chem. Soc. (1983), 105, 2776–2783].
(26) See L. Lebioda [Acta Cryst. (1980), B36, 271–275].
(27) n = 3 or 4; i.e. tri- or tetrasubstituted ureas.
(28) Overall value also includes structures with mean valence angle at N in the range 115–118°.
(29) See F. H. Allen & A. J. Kirby [J. Am. Chem. Soc. (1984), 106, 6197–6200].
(30) See A. J. Kirby (1983). [The anomeric effect and related stereoelectronic effects at oxygen. Berlin: Springer.]
(31) See B. Fuchs, L. Schleifer & E. Tartakovsky [Nouv. J. Chim. (1984), 8, 275–278].
(32) See S. C. Nyburg & C. H. Faerman [J. Mol. Struct. (1986), 140, 347–349].
(33) Sample dominated by P—CH₃ and P—CH₂—C.
(34) Sample dominated by C* = methyl.
(35) See A. Kálmán, M. Czugler & G. Argay [Acta Cryst. (1981), B37, 868–877].
(36) Bimodal distribution resolved into 22 `short' bonds and 5 longer outliers.
(37) All 24 observations come from BUDTEZ.
(38) `Long' O—H bonds in centrosymmetric $[{\rm O} \cdots {\rm H} \cdots {\rm O}]$ H-bonded dimers are excluded.
(39) N—N bond length also dependent on torsion angle about N—N bond and on nature of substituent C atoms – these effects are ignored here.
(40) N pyramidal has average angle at N in the range 100–113.5°; N planar has average angle ≥ 117.5°.
(41) See R. R. Holmes & J. A. Deiters [J. Am. Chem. Soc. (1977), 99, 3318–3326].
(42) No detectable variation in S=O bond length with type of C substituent.

Appendix A9.5.2

A9.5.2. Short-form references to individual CSD entries cited by reference code in Table 9.5.1.1

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REFCODE	Journal	Vol.	Page	Year
ACBZPO01	J. Am. Chem. Soc.	97	6729	1975
ACLTEP	J. Organomet. Chem.	184	417	1980
ASAZOC	Dokl. Akad. Nauk SSSR	249	120	1979
BALXOB	J. Am. Chem. Soc.	103	4587	1981
BAPPAJ	Inorg. Chem.	20	3071	1981
BARRIV	Acta Chem. Scand. Ser. A	35	433	1981
BAWFUA	Cryst. Struct. Commun.	10	1345	1981
BAWGAH	Cryst. Struct. Commun.	10	1353	1981
BECTAE	J. Org. Chem.	46	5048	1981
BELNIP	Z. Naturforsch. Teil B	37	299	1982
BEMLIO	Chem. Ber.	115	1126	1982
BEPZEB	Cryst. Struct. Commun.	11	175	1982
BETJOZ	J. Am. Chem. Soc.	104	1683	1982
BETUTE10	Acta Chem. Scand. Ser. A	30	719	1976
BIBLAZ	Zh. Strukt. Khim.	22	118-4	1981
BICGEZ	Z. Anorg. Allg. Chem.	486	90	1982
BIHXIZ	J. Chem. Soc. Chem. Commun.		982	1982
BIRGUE10	Z. Naturforsch. Teil B	38	20	1983
BIRHAL10	Z. Naturforsch. Teil B	37	1410	1982
BIZJAV	J Organomet. Chem.	238	C1	1982
BOGPOC	Z. Naturforsch. Teil B	37	1402	1982
BOGSUL	Z. Naturforsch. Teil B	37	1230	1982
BOJLER	Z. Anorg. Allg. Chem.	493	53	1982
BOJPUL	Acta Chem. Scand. Ser. A	36	829	1982
BOPFER	Chem. Ber.	116	146	1983
BOPFIV	Chem. Ber.	116	146	1983
BOVMEE	Acta Cryst. Sect. B	38	1048	1982
BQUINI	Acta Cryst. Sect. B	35	1930	1979
BTUPTE	Acta Chem. Scand. Ser. A	29	738	1975
BUDTEZ	Z. Naturforsch. Teil B	38	454	1983
BUPSIB10	Z. Anorg. Allg. Chem.	474	31	1981
BUSHAY	Z. Naturforsch. Teil B	38	692	1983
BUTHAZ10	Inorg. Chem.	23	2582	1984
BUTSUE	J. Chem. Soc. Chem. Commun.		862	1983
BUWZUO	Acta Chem. Scand. Ser. A	37	219	1983
BZPRIB	Z. Naturforsch. Teil B	36	922	1981
BZTPPI	Inorg. Chem.	17	894	1978
CAHJOK	Inorg. Chem.	22	1809	1983
CAJMAB	Chem. Z.	107	169	1983
CANLUY	Tetrahedron Lett.	24	4337	1983
CASSAQ	J. Struct. Chem.	2	101-2	1983
CASTOF10	Acta Cryst. Sect. C	40	1879	1984
CASYOK	J. Struct. Chem.	2	107-2	1983
CECHEX	Z. Anorg. Allg. Chem.	508	61	1984
CECXEN	J. Struct. Chem.	2	207-3	1983
CEDCUJ	J. Org. Chem.	48	5149	1983
CEHKAB	Z. Naturforsch. Teil B	39	139	1984
CELDOM	Acta Cryst. Sect. C	40	556	1984
CESSAU	Acta Cryst. Sect. C	40	653	1984
CETTAW	Chem. Ber.	117	1089	1984
CETUTE	Acta Chem. Scand. Ser. A	29	763	1975
CEYLUN	Isv. Akad. Nauk SSR Ser. Khim.		2744	1983
CIFZUM	Acta Chem. Scand. Ser. A	38	289	1984
CIHRAM	Angew. Chem. Int. Ed. Engl.	23	302	1984
CILRUK	J. Chem. Soc. Chem. Commun.		1023	1984
CILSAR	J. Chem. Soc. Chem. Commun.		1021	1984
CIMHIP	Acta Cryst. Sect. C	40	1458	1984
CINTEY	Dokl. Acak. Nauk SSSR	274	615	1984
CIPBUY	J. Struct. Chem.	2	281-4	1983
CISMUM	Z. Naturforsch. Teil B	39	485	1984
CISTED	Z. Anorg. Allg. Chem.	511	95	1984
CIWYIQ	Inorg. Chem.	23	1946	1984
CIYFOF	Inorg. Chem.	23	1790	1984
CMBIDZ	J. Org. Chem.	44	1447	1979
CODDEE	Z. Naturforsch. Teil B	39	1257	1984
CODDII	Z. Naturforsch. Teil B	39	1257	1984
COFVOI	Z. Naturforsch. Teil B	39	1027	1984
COJCUZ	Chem. Ber.	117	2686	1984
COSDIX	Z. Naturforsch. Teil B	39	1344	1984
COZPIQ	Chem. Ber.	117	2063	1984
COZVIW	Z. Anorg. Allg. Chem.	515	7	1984
CTCNSE	J. Am. Chem. Soc.	102	5430	1980
CUCPIZ	J. Am. Chem. Soc.	106	7529	1984
CUDLOC	J. Cryst. Spectrosc.	15	53	1985
CUDLUI	J. Cryst. Spectrosc.	15	53	1985
CUGBAH	Acta Cryst. Sect. C	41	476	1985
CXMSEO	Acta Cryst. Sect. B	29	595	1973
DGLYSE	Acta Cryst. Sect. B	31	1785	1975
DMESIP01	Acta Cryst. Sect. C	40	895	1984
DSEMOR10	J. Chem. Soc. Dalton Trans.		628	1980
DTHIBR10	Inorg. Chem.	10	697	1971
EPHTEA	Inorg. Chem.	19	2487	1980
ESEARS	J. Chem. Soc. C		1511	1971
ETEARS	J. Chem. Soc. C		1511	1971
FMESIB	J. Organomet. Chem.	197	275	1980
FPHTEL	J. Chem. Soc. Dalton Trans.		2306	1980
FPSULF10	J. Am. Chem. Soc.	104	1683	1982
HCLENE10	Acta Cryst. Sect. B	38	3139	1982
HMTITI	Acta Cryst. Sect. B	31	1505	1975
HMTNTI	Z. Anorg. Allg. Chem.	409	237	1974
HXPASC	J. Chem. Soc. Dalton Trans .		1381	1975
IBZDAC11	J. Chem. Soc. Dalton Trans.		854	1979
IFORAM	Monatsh. Chem.	105	621	1974
IODMAM	Acta Cryst. Sect. B	33	3209	1977
IPMUDS	Acta Cryst. Sect. B	29	2128	1973
ISUREA10	Acta Cryst. Sect. B	28	643	1972
LITMEB10	J. Am. Chem. Soc.	97	6401	1975
MESIAD	Z. Naturforsch. Teil B	35	789	1980
METAMM	Acta Cryst.	17	1336	1964
MNPSIL	J. Am. Chem. Soc.	91	4134	1969
MODIAZ	J. Heterocycl. Chem.	17	1217	1980
MOPHTE	Acta Chem. Scand. Ser. A	34	333	1980
MORTRS10	J. Chem. Soc. Dalton Trans.		628	1980
NAPSEZ10	J. Am. Chem. Soc.	102	5070	1980
NBBZAM	Z. Naturforsch. Teil B	32	1416	1977
OPIMAS	Aust. J. Chem.	30	2417	1977
OPNTEC10	J. Chem. Soc. Dalton Trans.		251	1982
PHASCL	Acta Cryst. Sect. B	37	1357	1981
PHASOC01	Aust. J. Chem.	28	15	1975
PNPOSI	J. Am. Chem. Soc.	90	5102	1968
SEBZQI	J. Chem. Soc. Chem. Commun.		325	1977
SPSEBU	Acta Chem. Scand. Ser. A	33	403	1979
TEACBR	Cryst. Struct. Commun.	3	753	1974
THINBR	J. Am. Chem. Soc.	92	4002	1970
TMPBTI	Acta Cryst. Sect. B	31	1116	1975
TPASSN	J. Chem. Soc. Dalton Trans.		514	1977
TPASTB	Cryst. Struct. Commun.	5	39	1976
TPHOSI	Z. Naturforsch. Teil B	34	1064	1979
TTEBPZ	Z. Naturforsch. Teil B	34	256	1979
ZCMXSP	Cryst. Struct. Commun.	6	93	1977

Pages of the form n-m indicate page n of issue m.

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https://doi.org/10.1107/97809553602060000621