High-resolution 13C NMR spectra and long-range 13C 1H spin coupling constants in pyridine and 2-bromopyridine

Abstract

High-resolution proton undecoupled 13C NMR spectra (continuous wave mode) have been obtained for pyridine and 2-bromopyridine using the 13C isotope in natural abundance. Analysis of these spectra has provided all possible long-range 13CH coupling constants including their relative signs, all directly bonded 13CH coupling constants, and in some cases differences in the 13C isotope effects on the 1H chemical shifts for these compounds. The 13CH coupling constants in pyridine and the effects of a 2-bromo substituent on these parameters are discussed with respect to corresponding data in previously reported compounds and with values obtained from CNDO/2 and INDO calculations. Contributions from incomplete quadrupolar removal of the 13C 14N coupling constants to the 13C line widths have been calculated and compared with experimental values.