The Polarizability and Second Hyperpolarizability of the Phenyl Cation

The phenyl cation has been the subject of special interest since 1942, when it was proposed as an in termediate in the decomposi t ion of the benzene d iazonium ion [ 1 5 ] . The objective of this communica t ion is to discuss the change in the polarizabil i ty, a [6], and second hyperpolar izabi l i ty , y [6] of Q H 5 , resulting f rom geometry variat ions of this cation. In addi t ion these variations are related to the stability of C6H5. The present s tudy is considered t imely and of current interest because: (a) Very little is known concerning the electric moments (permanent and induced) of molecular cations [7]. (b) Quest ions related to the potential impor tance of environmental factors on the isomerizat ion process of the phenyl ium cation, as well as the propert ies of the ion itself have already been raised in the l i terature [5]. (c) The phenyl cation, due to the strong polarization of the system toward C + [1] and the d e r e a l i z a tion of positive charge (almost 70% of the positive charge is away f rom C + ) [1], is a significant model system for the study of polar izat ion p h e n o m e n a in positively charged molecular species.