## strain

https://doi.org/10.1351/goldbook.S06037
Strain is present in a @M03986@ or @T06471@ if the energy is enhanced because of unfavourable bond lengths, bond angles or dihedral angles ('@E01886@') relative to a standard. It is quantitatively defined as the standard @E02141@ of a structure relative to a strainless structure (real or hypothetical) made up from the same atoms with the same types of bonding. (The @E02141@ of formation of cyclopropane is $$53.6\ \text{kJ mol}^{-1}$$, whereas the @E02141@ of formation based on three 'normal' @M03881@ groups, from acyclic models, is $$-62\ \text{kJ mol}^{-1}$$. On this basis cyclopropane is destabilized by ca. $$115\ \text{kJ mol}^{-1}$$ of @ST07108@.)
See:
molecular entity
,
molecular mechanics calculation
,
transition structure
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1168 [Terms] [Paper]