Section 9.5.3.3. Use of the `Note' column

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.