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Tricyclo [3.1.1.03,6]hept-6-yl radicals were generated by bromine abstraction from 6-bromo-tricyclo[3.1.1.03,6] 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[3.1.1.03,6] heptane gave tricyclo [3.1.1.03,6]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 [3.1.1.03,6]hept-6-ylmethyl radical, estimated from e.p.r. experiments and also from reduction of 6-bromomethyltricyclo[3.1.1.03,6] heptane with tributyltin hydride, was found to be >5×109 s-1 at 298 K.

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Three naphtho[2,3-c]thiophene-4,9-diones (thienonaphthoquinones) have been prepared and their redox properties studied by chemical, electrochemical and EPR spectroscopic methods. All three quinones were readily reduced electrochemically to the corresponding radical anions and subsequently to dianions. The cyclic voltammograms showed evidence of ion pairing of the dianions. All three quinones were also electrochemically oxidised to radical cations. The structures and thermodynamic properties of the quinones, the radical cations, radical anions and dianions were studied by the semi-empirical AM1 method. The experimental redox potentials were found to correlate with the computed energies of the appropriate frontier MOs. The electrochemically generated radical anions were observed by EPR spectroscopy and shown to decay with secondorder kinetics. The rate constants increased as the electron-releasing character of the substituents in the benzene ring increased. The only EPR spectroscopically detectable radical cation was that from the 6,7-dimethoxynaphtho[2,3-c]thiophene-4,9-dione. Attempts by electrochemical and chemical methods to polymerise the thienonaphthoquinones were unsuccessful.