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°, or syn if it is less than 90°. (A further distinction is made between antiperiplanar, synperiplanar, anticlinal and synclinal.)
-
In the older literature the terms anti and syn were used to designate stereoisomers of oximes and 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 That usage was superseded by the terms 'trans' and 'cis' or E and Z, respectively.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 reactions or transformations, 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 always antarafacial, and syn processes are suprafacial.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1084
PAC, 1996, 68, 2193
(Basic terminology of stereochemistry (IUPAC Recommendations 1996))
on page 2199
InChI=1/C6H10BrF/c7-5-3-1-2-4-6(5)8/h5-6H,1-4H2
InChI=1/C6H9Br/c7-6-4-2-1-3-5-6/h4H,1-3,5H2
InChI=1/C7H12/c1-7-5-3-2-4-6-7/h5H,2-4,6H2,1H3
InChI=1/C12H14/c1-3-7-11(8-4-1)12-9-5-2-6-10-12/h1,3-4,7-9H,2,5-6,10H2
InChI=1/C4H8/c1-3-4-2/h3-4H,1-2H3/b4-3+
InChI=1/C4H8Br2/c1-3(5)4(2)6/h3-4H,1-2H3/t3-,4+
AZQRVGXSORXOCR-UHFFFAOYAU
QBUMXSSCYUMVAW-UHFFFAOYAS
CTMHWPIWNRWQEG-UHFFFAOYAY
WCMSFBRREKZZFL-UHFFFAOYAN
IAQRGUVFOMOMEM-ONEGZZNKBD
BXXWFOGWXLJPPA-ZXZARUISBN
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.
