Strain is present in a
molecular entity or
transition structure if the energy is enhanced because of unfavourable bond lengths, bond angles or dihedral
angles ('
torsional strain') relative to a standard. It is quantitatively defined as the standard
enthalpy of a structure relative to a strainless structure (real or hypothetical) made up
from the same atoms with the same types of bonding. (The
enthalpy of formation of cyclopropane is
,
whereas the
enthalpy of formation based on three '
normal'
methylene groups, from acyclic models, is
.
On this basis cyclopropane is destabilized by
ca.
of
strain energy.)
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1168
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.
