Deuterium isotope effects on nuclear shielding constants and spin-spin coupling constants in the ammonium ion, ammonia, and water

Abstract

Deuterium isotope effects on 15N chemical shifts have been investigated for the ammonium ion, ammonia, and aniline; 1δ15N(2/1H)equats -293.3, -622.9, and -714.6 ppb respectively. Deviations fromadditivity arenoted forNH4-nDn+ and NH3-n Dn; these deviations follow the predictions of Jameson and Osten. For ammonia, examination of the proton nuclear magnetic resonance spectrum yields 1δ1H(15/14N) = -2.0 ± 0.4 ppb and 2δ1H(2/lH) -28.6ppb. An accurate value of -1545 ± 5 ppb was obtained for 1δ17O(2/1H) in water. Derivatives of the heavy atom shielding constants with respect to extensions in the equilibrium bond length have been estimated for NH4+NH3, and H2O; these derivatives are compared with the recent calculations of Chesnut. Deuterium isotope effects on 1J(15N,H) in ammonia and aniline have been measured for the first time. For the ammonium ion, deutecium isotope effects on 1J(15N,H) are in good agreement with the less accurate values we previously observed on 1J(14N,H). In the case of water, both primary and secondary deuterium isotope effects on 1J(17N,H) are less than 2%. The isotope effects on the spin-spin coupling constants observed here are compared with those previously reported for other hydrides in the literature.