[IUCr Home Page] [CIF Home Page]

Index

Macromolecular dictionary (mmCIF) version 2.0.09

_chem_comp.formula

Name:
'_chem_comp.formula'

Definition:

   The formula for the chemical component. Formulae are written
   according to the following rules:

   (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), but in general parentheses are
      not used.

   (4) The order of elements depends on whether carbon is
      present or not. 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 alphabetic order of their symbol. This
      is the 'Hill' system used by Chemical Abstracts.

Example:

'C18 H19 N7 O8 S'

Type: text

Mandatory item: no

Category: chem_comp