Two-Dimensional (2D-J) NMR Spectroscopy for Analysis of Isomers and Heterocouplings

Introduction NMR spectra can be recorded by displaying the intensity of absorption not only as a function of one frequency but also as a function of a second or third variable. This original idea has been suggested by Jeener in 1971 [1] and since then the basic principles and some pioneer experiments of multidimensional NMR spectroscopy have been developed by several groups [2, 3]. In particular, it has become possible to record two dimensional NMR spectra (a twodimensional NMR spectrum is a plot of intensity versus two frequency variables). The basic principles of this technique (2D-NMR) have been worked out by Ernst [4] and Freeman [5]. Recently it has been shown that 2 D-NMR is suitable for the study of a variety of phenomena, such as multiquantum transitions [6], 13C-13C coupling constants in natural abundance spectra [7] or exchange phenomena [8]. A special case of 2D-spectroscopy is 2D-J resolved spectroscopy [4, 5]. For weakly coupled spins in 2D-J NMR the chemical shift of a nucleus is displayed in one dimension and the coupling of the nuclei with each other (or with an other magnetically active nucleus) is displayed in the second frequency dimension.