1.1 Chemical names and structures must be portrayed correctly and unambiguously in pharmacopoeias and other compendia. For details of nomenclature conventions, readers are referred to the recommendations of the International Union of Pure and Applied Chemistry (1, 2).
1.2 These guidelines are intended to help scientists draw structural formulae correctly. They are only recommendations, however, because unwavering adherence to these principles is not always practicable. Thus, the guidelines should be followed closely wherever possible, but may be adapted, with certain exceptions, where necessary to produce accurately drawn structural formulae. Details of the formulae, such as bond lengths, the position of subscripts and superscripts, and the closeness of apposition of individual atomic symbols, will depend on the drawing method used, whether computer-based or manual.
1.3 Where possible, the structures are:
- set out horizontally rather than vertically;
- designed to be read from left to right; the highest-numbered atom in an acyclic structure should be on the left, the systematic numbering decreasing from left to right.
1.4 The numbering of rings is consistent with established chemical nomenclature. Where practicable, rings should be numbered in a clockwise direction.
1.5 Links between atoms and/or groups are represented by dashes. The structures should by and large be shown in full, with the complete rings. However, certain very common groups of atoms are shown in a more condensed form, as follows:
1.6 Symbols for groups of this kind, such as -Me, -Et, -Pr, -Ph, etc., are often used as a means of saving space.
1.7 The bulky group tert-butyl (1,1-dimethylethyl) is often shown as -C(CH3)3. Hydroxymethyl and aminomethyl groups can be represented in either expanded or condensed form:
-CH2-OH or -CH2OH
-CH2-NH2 or -CH2NH2
1.8 A polyatomic group is set out such that the atom that is directly attached to the rest of the structure is shown closest to the connecting dash:
1.9 The carbonyl group in ketones is depicted as:
In aldehydes it is depicted in the condensed rather than expanded form:
1.10 The sulfonyl group is depicted as:
rather than in the condensed form -SO2-
The sulfinyl group is shown as:
rather than in the condensed form -SO-; the last representation is useful as a means of recognizing a chiral compound: