A theoretical study on the protonation of cycloalkanes CnH2n (n = 3 to 6)

Ab initio self-consistent-field molecular orbital calculations have been carried out for the C_nH_2n (n = 3 to 6) cycloalkanes and various conformers of their protonated forms. The calculated protonation energies for the sequence of conformers of the protonated forms follow the experimentally observed trend. Correlations between optimum C? C? C bond angles at the protonation site and the calculated protonation energies have been observed, and these correlations may be of some use in estimating protonation energy-bond angle relations in other (strained) cyclic compounds when the central carbon atom of a C? C? C moiety is protonated.