NMR Study of Substituted Bicyclo[3.2.1]octanes

Abstract

The 1H and 13C NMR spectra of six bromo- and methoxybicyclo[3.2.1]octanes were completely assigned. An axial bromine substituent at C-2 or C-4 results in a 5 ppm upfield shift of C-8 due to the gauche interaction. An equatorial bromine results in an upfield shift of similar magnitude on either C-6 (or C-7) due to a similar gauche interaction but has little effect on the chemical shift of C-8. The 1,4-anti interaction of an axial bromine substituent on carbons C-6 and/or C-7 results in a small upfield shift (0.3 ppm) in parallel to the effect of an equatorial bromine on the chemical shift of C-8. Similarly to the trend observed in bicyclo[2.2.1]heptanes, the substituent effects for 1,4-gauche and 1,4-anti interactions of the methoxy group are larger than for bromine.