Racemisation and oxygen exchange reactions of the trimethylnorbornan-2-ols

Abstract

The rates of acid-catalysed heterolysis of the C–O bond of borneol (bornan-2,endo-ol), isoborneol (bornan-2,exo-ol), camphene hydrate (2,3,3-trimethylnorbornan-2,exo-ol), and methylcamphenilol (2,3,3-trimethylnorbornan-2,endo-ol) have been measured. Camphene hydrate exchanges oxygen in aqueous acid more rapidly than it racemises by a factor of 38, while methyl camphenilol rearranges to a mixture of camphene hydrate and isoborneol, the C–O bond heterolysis being slower than that of camphene hydrate by a factor of 1·3 × 10³. Isoborneol both racemises and exchanges oxygen at the same rate, faster than borneol by a factor of 2·3 × 10⁵. The rate ratios for both pairs of alcohols are considered to be electronic as well as steric in origin.