Nuclear magnetic resonance shift reagents in organic chemistry

The paper deals with the implications of shift reagents in organic chemistry in several broad areas. First, the relative binding affinities of common functional groups to shift reagents are considered, and it is shown that such knowledge aids the analysis of the shifted spectra of polyfunctional molecules and (by extension ofthe principles involved) isotopically substituted molecules. Secondly, the quantitative application of the pseudo-contact shift equation is considered, and the importance of considering the population of two or more energy minima associated with conformational mobility in the shift reagent/ substrate complex is emphasized. In the most adverse cases, observed shifts must be separated into (i) complex formation shifts (ii) contact shifts and (iii) pseudo-contact shifts. Thirdly, the potential of shift reagents in biology and 13C n.m.r. is briefly outlined. Finally, some miscellaneous applications are given.