EFFECT OF ALKYL SUBSTITUTION ON THE EASE OF OXIDATION OF BICYCLO[1.1.0]BUTANES - EXPERIMENTAL-VERIFICATION OF PRDDO CALCULATIONS FOR THE NATURE OF THE HOMO OF BICYCLO[1.1.0]BUTANE

Bicyclo[1.1.0]butane and eight methylated derivatives were synthesized and the oxidative half-wave potentials of each of these nine compounds were measured vs. a saturated calomel electrode by using single sweep voltammetry. The half-wave potentials varied from 1.69 V for bicyclo[1.1.0]butane to0.93 V for 1,2,2,3,4,4-hexamethylbicyclo[1.1.0]butane. Bridgehead substitution resulted in an average decrease in half-wave potential of 0.29 V per methyl group, while methyl substitution at either the 2-or 4-position resulted in only a 0.05 V average decrease. Molecular orbital calculations using the partial retention of diatomic differential overlap (PRDDO) method gave the wave functions for each of the compounds studied. The vertical ionization potentials for each of the 29 possible methylated bicyclo[1.1.0]butanes and for the parent hydrocarbon were obtained via Koopmans’ theorem. In all cases, methyl substitution was found to lower the ionization potential. The largest effect was found for bridgehead substitution and the smallest effect resulted from substitution at the 2-and 4-exo positions. The experimentally obtained oxidative half-wave potentials correlated with the calculated vertical ionization potentials with r = 0.978. These results provide strong evidence in support of the theoretical predictions that the HOMO of bicyclo[1.1.0]butane is localized in the C1-C3 bond. © 1979, American Chemical Society. All rights reserved.