Conformations referring to torsion
angles θ (A, B, C, D), where A, B, C, D are main-chain atoms,
can be described as:
cis or
synperiplanar();gauche or
synclinal();anticlinal(); and
trans
or
antiperiplanar(), corresponding to torsion angles within
± 30° of, respectively, 0°, ± 120° and ± 180°. The letters shown in parentheses (upper
case
,
,
,
) are the recommended abbreviations. The symbols
,
(or
,
, for example) refer to torsion angles of similar type but opposite known
sign, i.e.
~ +60°, ~ -60° (or ~ +120°, -120° ). The notation
,
;
,
(and
,
;
,
- whenever the torsion angles are not exactly equal to 180° and 0°,
respectively)
is reserved for the designation of
enantiomorph conformations,
i.e. conformations of op- posite but unspecified sign. Where necessary,
a
deviation from the proper value of the
torsion angle can be indicated by the sign (~), as in the
following examples:
;
;
.
Source: