Mishra Sandeep Kumar, Suryaprakash N
Department of Physics and NMR Research Centre, Indian Institute of Science Education and Research, Pune 411008, India.
NMR Research Centre and Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India.
Prog Nucl Magn Reson Spectrosc. 2023 Aug-Oct;136-137:1-60. doi: 10.1016/j.pnmrs.2023.02.001. Epub 2023 Feb 7.
The scalar couplings that result in the splitting of the signals in the NMR spectrum arise due to the interaction 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 H 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 extraction of the coupling constants from the H spectrum of a complex spin system continues to remain a challenge, 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 broadband 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 (J, where n = 1,2,3) while retaining the high resolution obtained by implementing 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.
导致核磁共振谱中信号分裂的标量耦合是由于核自旋的相互作用产生的，自旋极化通过化学键传递。相互作用强度尤其取决于两个相互作用自旋之间连续化学键的数量以及分子构象。分子中许多自旋的成对相互作用导致复杂的光谱，这对光谱分析以及同核和异核耦合的大小和符号的确定构成了严峻挑战。由于化学位移分散通常非常小，在氢谱分析中这个问题比大多数其他原子核的光谱分析更为严重。因此，从复杂自旋系统的氢谱中直接分析和准确提取耦合常数仍然是一个挑战，而且往往可能是一项艰巨的任务。多年来，该领域的研究人员开发了几种基于纯位移的一维和二维方法，这些方法提供质子光谱的宽带同核去耦，消除了复杂性，但代价是损失了非常有信息价值的标量耦合。为了规避这个问题，已经开发了几种一维和二维核磁共振实验来测定同核和异核耦合（Jn, 其中n = 1,2,3），同时保留通过实施纯位移策略获得的高分辨率。这篇综述试图总结多年来大量研究人员为准确测定同核和异核标量耦合所报道的广泛工作。
