Deuterium isotope effects on the nitrogen chemical shift and 1J(N,H) in the ammonium ion

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Abstract
The effect of successive deuterium substitution on the nitrogen‐14 nuclear shielding constant and 1J(14N,H) in the ammonium ion has been measured. Each additional replacement of hydrogen by deuterium resulted in an approximately 0.30 ppm increase in the nitrogen shielding. This is less than half that previously reported for liquid ammonia and approximately twice that reported for methane. These observations can be qualitatively accounted for by the theoretical model of Jameson. A measurable secondary deuterium isotope effect of 1J(14N,1H) was observed: on going from NH+4 to NHD+3 , 1J(14N,1H) decreased by 0.15±0.03 Hz. The primary isotope effect on 1J(14N,H) is less than 0.2 Hz.