Isotope effect due to [formula omitted] substitution on 14N 14N coupling constants in nitrous oxide

Abstract

14N and 17O NMR spectra of a solution of nitrous oxide, NNO in acetonitrile were measured on a Bruker AM 300 spectrometer. The 14N NMR spectrum reveals two narrow lines at about −147 and −231 ppm relative to external nitromethane assigned to the central and terminal nitrogen atoms, respectively. Both lines exhibit mutual spin-spin splittings equal to 4.233 (±0.006) Hz. The 17O NMR spectrum also reveals a rather narrow line with a chemical shift of 110 ppm relative to external water with a clearly seen 1:1:1 triplet structure due to a 1J( 14 N 17 O) coupling constants of 35.8 (±0.3) Hz. Accurate experimental values were obtained using the quadr program. Comparison of the 1J( 14 N 14 N) coupling constant measured in the present study with 1J( 15 N 15 N) coupling constant equal to −9.16 (±0.3) Hz (or −4.65 (±0.2) Hz on the basis of 14 N 14 N coupling constants) obtained previously by Bhattacharrya and Dailey reveals a strong, double primary isotope effect of about 10%. This can be considered as one of the largest isotope effects on coupling constants ever measured.