Nitrogen-15 magnetic resonance spectroscopy, I. Chemical shifts

Except for the original determination(1) of nuclear moments, nitrogen magnetic resonance spectroscopy has been limited to the isotope of mass number 14. Although N14 is an abundant isotope, it possesses an electric quadrupole moment, which seriously broadens the resonances of nitrogen in all but the most symmetrical of environments.(2) Consequently, nitrogen n.m.r. spectroscopy has seen only limited use in the determination of organic structure. It might be expected that N15, which has a spin of ½ and no quadrupole moment, would be very useful, but the low natural abundance (0.36%) and the inherently low signal intensity (1.04 x 10^(-3) that of H1 at constant field) have thus far precluded utilization of N15 in n.m.r. spectroscopy.(3)