CONFORMATIONAL S-CIS TRANS ISOMERIZATION IN FREE-RADICALS OBSERVED BY MUON LEVEL-CROSSING RESONANCE SPECTROSCOPY

A rare type of cis-trans isomerism arises from restricted rotation about a single C-C bond and has been seen here by level crossing resonance spectroscopy (LCR) in muonated free radicals. Itis observed as a splitting of the proton's LCR when the C-atom adjacent to the unpaired electron density is an asymmetric sp2 hybrid. Free radicals which contain C's with sp3, symmetric sp2, or sp hybrid bonds do not show this geometric isomerism. The α-protons on these radicals show resolvable splitting less easily than the β-protons. The radicals observed are those resulting from formal addition of muonium to the C=C bonds of acrylates, and they occur regardless of whether the compounds are studied in dilute aqueous solution or as pure liquids. © 1990, American Chemical Society. All rights reserved.