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: