ISOTOPE EFFECT DUE TO N-15 N-14 SUBSTITUTION ON N-14-N-14 COUPLING-CONSTANTS IN NITROUS-OXIDE/

N-14 and O-17 NMR spectra of a solution of nitrous oxide, NNO in aceto nitrile were measured on a Bruker AM 300 spectrometer. The N-14 NMR sp ectrum reveals two narrow lines at about -147 and -231 ppm relative to external nitromethane assigned to the central and terminal nitrogen a toms, respectively. Both lines exhibit mutual spin-spin splittings equ al to 4.233 (+/-0.006) Hz. The O-17 NMR spectrum also reveals a rather narrow line with a chemical shift of 110 ppm relative to external wat er with a clearly seen 1:1:1 triplet structure due to a (1)J(N-14-O-17 ) coupling constants of 35.8 (+/-0.3) Hz. Accurate experimental values were obtained using the QUADR program. Comparison of the (1)J(N-14-N- 14) coupling constant measured in the present study with (1)J(N-15-N-1 5) coupling constant equal to -9.16 (+/-0.3) Hz (or -4.65 (+/-0.2) Hz on the basis of N-14-N-14 coupling constants) obtained previously by B hattacharrya and Dailey reveals a strong, double primary isotope effec t of about 10%. This can be considered as one of the largest isotope e ffects on coupling constants ever measured.