Towards a complete account of the exchange chemistry of a diastereotopic proton pair. I. Base-catalyzed enolizationexchange of 2-norbornanones; on the rate controlling factors

We report the rates of base-catalyzed hydrogen isotope exchange of the exo and endo protons in a series of 2-norbornanones. The exo:enclo rate ratios for 4-methyl-substituted 2-norbornanones 3 and 6 are less than the rate ratios of the 4-demethyl analogs 2 and 5. Therefore, a methyl group is not a useful torsional-effect probe. This is supported by an analysis which established that the small difference in the torsional strain (0.45 kcal) …