An electron spin resonance investigation of β-substituted 1,1-diphenylethyl radicals

Abstract

A large number of β-substituted 1,1-diphenylethyl derivatives Ph₂ĊCH₂MR_n have been generated by addition of ·MR_n radicals to 1,1-diphenylethylene. The magnitude of the β-proton hyperfine splitting constants together with the observation of linewidth alternation effects on the CH₂ triplet, indicate that the preferred conformation of these radicals is close even though not coincident with that placing the MR_n group in an eclipsed position with respect to the 2p_z orbital on C_α. The slight departure of these adducts from an eclipsed geometry has been interpreted as due to the presence on C_α of the two phenyl rings which are somewhat twisted with respect to each other thus producing an asymmetric potential around the radical centre. Although all the 1,1-diphenylethyl derivatives which have been investigated adopt the same conformation, the β-proton splitting cover the range from 6 to 11 G. The two common interpretations invoked to explain the effect of β-substituents on this splitting are discussed.