Index

Core dictionary version 3.3.0

Category CHEMICAL_FORMULA

Parent category:
CHEMICAL

Definition:

   
    Data items in the CHEMICAL_FORMULA category specify the composition and
    chemical properties of the compound. The formula data items must agree
    with those that specify the density, unit-cell and Z values.

    The following rules apply to the construction of the data items
    _chemical_formula.analytical, *.structural and *.sum. For the
    data item *.moiety the formula construction is broken up into
    residues or moieties, i.e. groups of atoms that form a molecular
    unit or molecular ion. The general rules given below apply within each
    moiety, but different requirements apply to the way that moieties
    are connected (see _chemical_formula.moiety).

    (1) Only recognized element symbols may be used.

    (2) Each element symbol is followed by a 'count' number. A count of
   '1' may be omitted.

    (3) A space or parenthesis must separate each cluster of (element
   symbol + count).

    (4) Where a group of elements is enclosed in parentheses, the
   multiplier for the group must follow the closing parentheses.
   That is, all element and group multipliers are assumed to be
   printed as subscripted numbers. [An exception to this rule
   exists for *.moiety formulae where pre- and post-multipliers
   are permitted for molecular units].

    (5) Unless the elements are ordered in a manner that corresponds to
   their chemical structure, as in _chemical_formula.structural,
   the order of the elements within any group or moiety
   depends on whether or not carbon is present. If carbon is
   present, the order should be: C, then H, then the other
   elements in alphabetical order of their symbol. If carbon is
   not present, the elements are listed purely in alphabetical order
   of their symbol. This is the 'Hill' system used by Chemical
   Abstracts. This ordering is used in _chemical_formula.moiety
   and _chemical_formula.sum.

       _chemical_formula.IUPAC      '[Mo (C O)4 (C18 H33 P)2]'
       _chemical_formula.moiety     'C40 H66 Mo O4 P2'
       _chemical_formula.structural '((C O)4 (P (C6 H11)3)2)Mo'
       _chemical_formula.sum         'C40 H66 Mo O4 P2'
       _chemical_formula.weight      768.81

Category is of type Set