Conformations referring to torsion angles $\uptheta\!$ ($\ce{A}$, $\ce{B}$, $\ce{C}$, $\ce{D}$), where $\ce{A}$, $\ce{B}$, $\ce{C}$, $\ce{D}$ are main-chain atoms, can be described as: cis or synperiplanar (\(\rm{C}\)); gauche or synclinal (\(\rm{G}\)); anticlinal (\(\rm{A}\)); and trans or antiperiplanar (\(\rm{T}\)), corresponding to torsion angles within $\pu{\pm 30\!^{\circ}}$ of, respectively, $\pu{\pm 0\!^{\circ}}$, $\pu{\pm 120\!^{\circ}}$ and $\pu{\pm 180\!^{\circ}}$. The letters shown in parentheses (upper case \(\rm{C}\), \(\rm{G}\), \(\rm{A}\), \(\rm{T}\)) are the recommended abbreviations. The symbols \(\rm{G}^{+}\), \(\rm{G}^{-}\) (or \(\rm{A}^{+}\), \(\rm{G}^{-}\), for example) refer to torsion angles of similar type but opposite known sign, i.e. $\pu{\sim +60^{\circ}}$, $\pu{\sim -60^{\circ}}$ (or $\pu{\sim +120^{\circ}}$, $\pu{\sim -120^{\circ}}$). The notation \(\rm{G}\), \(\bar{\rm{G}}\) ; \(\rm{A}\), \(\bar{\rm{A}}\) (and \(\rm{T}\), \(\bar{\rm{T}}\) ; \(\rm{C}\), \(\bar{\rm{C}}\) - whenever the torsion angles are not exactly equal to $\pu{180\!^{\circ}}$ and $\pu{0\!^{\circ}}$, respectively) is reserved for the designation of enantiomorph conformations, i.e. conformations of opposite but unspecified sign. Where necessary, a deviation from the proper value of the torsion angle can be indicated by the sign ($\sim$), as in the following examples: \(\rm{G(\sim)}\); \(\rm{G}^{+}(\sim)\); \(\rm{G}^{-}\rm{(\sim)}\).