Electronic structure and conformational equilibria of phenyl-propylcarbocations

Abstract

Modified CNDO calculations were performed on different conformations of various phenyl propyl cations and related compounds. Molecular energies and electronic structures are presented and discussed. A substituted secondary benzyl cation, the 1-phenyl-1-propyl carbocation ( 12) is found to be the most stable isomer. The open chain 1-phenyl-2-propyl carbocation ( 11b) has a lower energy than the propylene benzenium cation ( 11d). In contrary, previous calculations of 2-phenyl-1-ethyl cation lead to the result that in this case the ethylene benzenium cation is the most stable structure. Rotational barriers for different substituted 1-propyl and 2-propyl cations were calculated. The results are explained by hyperconjugative stabilization.