The nuclear shielding derivative and spin–spin coupling in nitrogen

Abstract

The 15N/14N isotope shift on the 15N chemical shielding in a mixture of 15N14N and 15N15N was found to be 0.0601±0.0022 ppm. Using a model developed by Jameson, the nuclear shielding derivative with respect to bond length was calculated from the measured isotope shift, [∂σ(15N)/∂r]e =−910±42 ppm/Å. This value is in excellent agreement with a value obtained from the temperature dependence of the shielding constant in the gas phase (at the zero pressure limit) and with a value determined from recent molecular orbital calculations. From relaxation measurements the scalar spin–spin coupling constant, 1J(14N,15N), in 14N15N was calculated to be 1.8±0.6 Hz which gives a reduced coupling constant, 1K(N,N)=2.0±0.7 (1020)m−2kg s−2 Å−2. The magnitude of the reduced coupling constant is compared to that of other isoelectronic species and molecular orbital calculations.