What are homodesmotic reactions?
A homodesmotic reaction (from Greek homos "same" + desmos "bond") is a reaction in which the reactants and products contain equal numbers of
- carbon atoms in the same state of hybridization
- CH₃, CH₂, and CH groups
This matching of hybridization and groups makes it easier to evaluate strain energy in rings such as cyclopropane.
An example of a homodesmotic reaction is
cyclo-(CH₂)₃ + 3CH₃-CH₃ → 3CH₃CH₂CH₃;
All C atoms are sp² hybridized, and there are six CH₃ and three CH₂ groups on each side of the equation.
Since all bond types and groups are matched, the value of