Abstract
The structures of various para-substituted biphenyls (Bp-X; X = -OH, -OCH3, -CH3, -H, -CONH2, -COOH, and -CN) and their radical anions (Bp-X(•-)) were investigated by time-resolved resonance Raman spectroscopy combined with pulse radiolysis. The inter-ring C1-C1' stretching modes (ν6) of Bp-X were observed at ∼1285 cm(-1), whereas the ν6 modes of Bp-X(•-) with an electron-donating or -withdrawing substituent were significantly up-shifted. The difference (Δf) between the ν6 frequencies of Bp-X and Bp-X(•-) showed a significant dependence on the electron affinity of the substituent and exhibited a correlation with the Hammett substituent constants (σp). In contrast to Bp-H(•-) with a planar geometry, the theoretical and experimental results reveal that all Bp-X(•-) with an electron-donating or -withdrawing substituent have a slightly twisted structure. The twisted structure of Bp-X(•-) is due to the localization of the unpaired electron and negative charge density on one phenyl moiety in Bp-X(•-).
Published Version
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