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These spectral editing techniques provide complementary strategies for the quantification of small J coupling constants. Performance of the existing techniques has been evaluated and the results show that these approaches can be adapted for a wide range of samples, ranging from complex chemical molecules to biological samples, even for the samples under inhomogeneous magnetic fields. One is to directly extract small J coupling constants without J multiplication, while another is on the basis of J multiplication.
![mestrenova substract spectrum mestrenova substract spectrum](https://docplayer.net/docs-images/102/155056815/images/19-1.jpg)
Generally, the existing techniques can be divided into two types. A cornucopia of NMR spectral techniques has been designed for the achievement of small J coupling information. However, the accurate measurement of small J coupling constants is limited by the natural linewidth since the line splitting arising from small J couplings are usually merged into the related peaks.
![mestrenova substract spectrum mestrenova substract spectrum](https://i.ytimg.com/vi/KZ_3z79qhp8/mqdefault.jpg)
Thus, accurate measurement for small J coupling constants is extremely important, which has long been recognized. Small J coupling constants are closely relevant to the assignment of conformational preferences for medium- to large-sized molecules and the valuable structural information about the backbone dihedral angles of biological molecules. Shuhui Cai, in Annual Reports on NMR Spectroscopy, 2011 Abstract