Estimating ring strain energies in small carbocycles by means of the Bader’s theory of ‘atoms-in-molecules’

In this Letter we report an easy way to estimate ring strain energies using the Bader’s theory of ‘atoms-in-molecules’. We demonstrate that the value of the Lagrange kinetic energy density at the ring critical point correlates with the ring strain energies in several three-, four-, five- and six-membered carbocycles, therefore it can be used as a measure of ring strain. Since it is easy to calculate and, in contrast to the ring strain energy calculations, it is free from other influences, as the number and type of reference molecules and type of reaction (isodesmic, homodesmotic, hyperhomodesmotic, etc.). Its use in heterocycles requires more investigation.