Magnetic resonance studies of cation radicals from chromans. Part 2.—Nuclear magnetic resonance, electron spin resonance, ENDOR and TRIPLE spectroscopy of some tricyclic chromans

Abstract

N.m.r. spectroscopy has been used to study the electron-exchange reaction between the substrate–radical pairs of 2,3,4,7,8,9-hexahydro-2,2,5,7,7,10-hexamethylbenzo[1,2-b : 4,5-b′]-dipyran, 2,3,4,5,6,7-hexahydro-2,2,7,7,9,10-hexamethylbenzo[1,2-b : 4,3-b′]dipyran and 2,3,6,7-tetrahydro-2,2,4,6,6,8-hexamethylbenzo[1,2,-b : 4,5-b′]difuran and their cation radicals. The rate constants and energetics of activation of the reactions have been determined, along with absolute signs of the averaged proton hyperfine coupling constants. ENDOR and TRIPLE measurements provided accurate values of the individual coupling constants and their relative signs: the n.m.r. and ENDOR data taken together gave a complete assignment.