Double resonance studies of isotope effects on nitrogen chemical shifts

The effect on nitrogen chemical shifts of 14N 15N isotopic substitution has been examined by 1H{14N} and 1H{15N} heteronuclear double resonance. For the four molecules (CH3)4N+I−, C6H6CH2NC, CH3ONO2 and (CH3)2NNO2 and their 15N anologs the ratio of 15N14N resonance frequencies is R = 1.40275695 ± 8 × 10-8. It is concluded that there is no significant isotope effect on the nitrogen shieldings and that R gives directly the ratio γ(15N)γ(14N).