Abstract:
The scalar couplings that result in the splitting of the signals in the NMR spectrum arise due to the inter-
action of the nuclear spins, whereby the spin polarization is transmitted through chemical bonds. The
interaction strengths depend inter alia on the number of consecutive chemical bonds intervening
between the two interacting spins and on the molecular conformation. The pairwise interaction of many
spins in a molecule resulting in a complex spectrum poses a severe challenge to analyse the spectrum and
hence the determination of magnitudes and signs of homo- and heteronuclear couplings. The problem is
more severe in the analysis of 1H spectra than the spectra of most of the other nuclei due to the often very
small chemical shift dispersion. As a consequence, the straightforward analysis and the accurate extrac-
tion of the coupling constants from the 1H spectrum of a complex spin system continues to remain a chal-
lenge, and often may be a formidable task. Over the years, the several pure shift-based one-dimensional
and two-dimensional methodologies have been developed by workers in the field, which provide broad-
band homonuclear decoupling of proton spectra, removing the complexity but at the cost of the very
informative scalar couplings. To circumvent this problem, several one-dimensional and two-
dimensional NMR experiments have been developed for the determination of homonuclear and
heteronuclear couplings (nJHX, where n = 1,2,3) while retaining the high resolution obtained by imple-
menting pure shift strategies. This review attempts to summarize the extensive work reported by a large
number of researchers over the years for the accurate determination of homo- and heteronuclear scalar
couplings.