N.M.R. spectra of molecules containing quadrupolar nuclei

Abstract

The general expression giving the N.M.R. band-shape of a spin-1/2 nucleus coupled to a spin-1 nucleus is considered in detail for the ‘fast-exchange’ limit, where the quadrupolar-induced relaxation rates of the spin-1 spin states are much greater than the coupling constant between the nuclei. The problem of obtaining the coupling constant from measurements on the band-shape of the spin-1/2 resonance is discussed, and it is concluded that this is only possible without further information when departures from lorentzian shape are observed. Possible sources of extra data are mentioned. The case of 3,4,5-trichloro-2,6-difluoropyridine is examined. The (N, F) coupling constant is obtained from the ¹⁵N satellites in ¹⁹F resonance. Hence values of the spin-lattice relaxation time for ¹⁴N are derived as a function of temperature.