ENDOR STUDY OF HINDERED INTERNAL ROTATION OF THE ALKYL GROUP IN THE 4,4′-DIISOPROPYL BIPHENYL ANION RADICAL

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Abstract Utilizing ENDOR observations for the 4,4′-diisopropylbiphenyl anion, the β-proton coupling constants were determined and their temperature dependence was investigated. The positive temperature dependence of the β-proton coupling constant was interpreted utilizing a revised model of restricted rotation for isopropyl groups (see Fig.3-b). The energy difference, Eo between the two equilibrium states of this restricted rotational system was estimated to be 0.4 Kcal/mol.