The approved stereodescriptors
of stereoisomeric alkenesR1R2C=CR3R4
need be different from
and related systems e.g.
The group of highest CIP priority
attached to one of the terminal doubly bonded atoms of the alkene, oxime, etc. or
is compared with the group of highest precedence attached to the other (i.e.
). The stereoisomer is designated as Z
(zusammen = together) if the groups lie on the same side of a reference plane passing
through the double bond and perpendicular to the plane containing the bonds linking
the groups to the double-bonded atoms; the other stereoisomer is designated as E
(entgegen = opposite). The descriptors may be applied to structures with a fractional
between one and two; and to double bonds involving elements other than carbon. They
are not used to describe ring substitution relationships.
PAC, 1996, 68, 2193
(Basic terminology of stereochemistry (IUPAC Recommendations 1996))
on page 2206
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