Department of Chemistry, University of Birmingham, Birmingham B15 2TT England
Department of Chemistry, Queen's University, Belfast BT9 5AG Northern Ireland
Abstract:
The geminal -methytene protons in 3-ethylnaphthalene-l,2-oxide show chemical shift nonequivalence in 1H NMR spectra recorded at ambient temperature consistent with a high barrier to enantiomerization via the orepine tautomer. The methylene protons in -benzoyloxytoluene-2,3-oxide which are a singlet at ambient temperature split into an AB system at -135 °C and there is evidence of ca. 5% of the oxepine isomer. Lineshape analysis of the coalescing arene oxide AB Signals provides the activation parameters for the valence isomerization/degenerate racemization process: ΔGXXX = 7.6 kcal mol-1, ΔHXXX = 8.6 kcal mol-l, ΔSXXX= 5.8 cal K-l mol-1.