A comparison of substituent effects on vicinal proton–proton and carbon–proton coupling constants

Abstract

Vicinal carbon–proton coupling constants have been determined for a series of tert-butyl derivatives and compared to the vicinal proton–proton coupling constants in the analogous series of isopropyl derivatives. In both series coupling constants were found to decrease with electronegativity of substituent, with 3JC,H decreasing more rapidly than 3JH,H. The relationship between the two types of coupling was found to be JC,H = 1.2JH,H − 3.5. The regular change in the ratio of JC,H to JH,H indicates that substituent effects can be useful in predicting carbon–proton coupling constants from proton–proton models.