NMR motional averaging in the isotopically perturbed cope rearrangement

The effect of deuterium substitution on the positional equilibrium and rate of the Cope rearrangement in barbaralone-d(1) has been investigated by H-1 and C-13 dynamic NMR spectroscopy. Deuterium favors the allylic position over the cyclopropyl position. Skewing of the equilibrium requires that the Cope rearrangement be considered as a nonmutual exchange process that transports C-13-H-1 spin pairs between unequally populated molecular configurations. The NMR fast-exchange results are critically interpreted in light of a recently proposed alternative averaging theory (Jones, D. Fl.; Kurur, N. D.; Weitekamp, D. P. Bull. Magn. Reson. 1992, 14, 214). Our experimental results are consistent with the traditional theory but do not agree with the prediction of the alternative theory. The use of H-1-C-13 inverse detection is demonstrated for the observation of very broad C-13 resonances in the coalescence region via their directly attached exchange-narrowed H-1 signals, and the contribution of rapid chemical exchange to the decay of heteronuclear zero-and double-quantum coherence is discussed.