https://doi.org/10.1351/goldbook.A00381
In the representation of stereochemical relationships 'anti' means 'on opposite sides' of a reference plane, in contrast to '
syn
' which means 'on the same side', as in the following examples.- Two substituents attached to atoms joined by a single bond are anti if the torsion angle(dihedral angle) between the bonds to the substituents is greater than 90°, orsynif it is less than 90°. (A further distinction is made betweenantiperiplanar,synperiplanar,anticlinalandsynclinal.)
- In the older literature the terms anti and synwere used to designatestereoisomersofoximesand related compounds. That usage was superseded by the terms 'trans' and 'cis' or E and Z, respectively.
- When the terms are used in the context of chemical reactionsortransformations, they designate the relative orientation of substituents in the substrate or product:
- Addition to a carbon-carbon double bond:
- Alkene-forming elimination:In the examples described under (1) and (2) anti processes are alwaysantarafacial, andsynprocesses aresuprafacial.
- Addition to a carbon-carbon double bond:
See also:
endo, exo, syn, anti