An E.P.R and Kinetic Investigation of Tricyclo[3.1.1.0^3,6]hept-6-yl and Tricyclo[3.1.1.0^3,6]hept-6-ylmethyl Radicals

Abstract

Tricyclo [3.1.1.0^3,6]hept-6-yl radicals were generated by bromine abstraction from 6-bromo-tricyclo[3.1.1.0^3,6] heptane , and observed by e.p.r. spectroscopy. In spite of their high ring strain the radicals were found not to rearrange readily but to take part in bimolecular combination reactions and to abstract hydrogen from the methylene groups of triethylsilane. Similar treatment of 6-bromomethyltricyclo[3.1.1.0^3,6] heptane gave tricyclo [3.1.1.0^3,6]hept-6- ylmethyl radicals, which rearranged so rapidly that only the product of β-scission, the 6-methylenebicyclo[3.1.1]hept-3-yl radical, was observed spectroscopically . The rate constant for β-scission of the tricyclo [3.1.1.0^3,6]hept-6-ylmethyl radical, estimated from e.p.r. experiments and also from reduction of 6-bromomethyltricyclo[3.1.1.0^3,6] heptane with tributyltin hydride, was found to be >5×10⁹ s-¹ at 298 K.