Density Functional Study of the Hexamethyl-(Dewar Benzene) Radical Cation and Some Related Compounds.

Abstract

A theoretical study has been undertaken of the hexamethyl(Dewar benzene) radical cation (both 2B2 and 2A1 states in C2v symmetry) as well as of two related ions, the pentamethylbenzene and the pentamethylbenzyl trifluoroacetate radical cations, which have been suggested as alternative assignments of the EPR spectrum attributed to the hexamethyl(Dewar benzene) cation. The geometries were optimized at the HF and LDA levels of theory using a standard 6-31G basis set. Single point calculations of the hyperfine coupling constants (hfcc) were then performed at the more accurate MP2, B3PW91, B3LYP and PWP86 levels using larger basis sets. The theoretical results of the present study support the assignment of 2B2 as the ground state of the hexamethyl(Dewar benzene) cation, yielding hydrogen atom hfcc’s in very good agreement with experiment.