Lanthanide-Induced Shifts (LIS) in Structural and Conformational Analysis

Abstract

The uses and applications of lanthanide induced shifts (LIS) in structural and conformational analysis are reviewed. The theoretical basis of LIS including contact, pseudocontact, and complexation shifts is considered and a reliable procedure for evaluating the pseudocontact shift at any nucleus is given. The simplified complexation models used in the LIRAS (lanthanide induced relaxation and shifts) suite of programs are described and their applications to structural analysis are discussed. This includes lutetium versus lanthanum in probing diamagnetic shifts, the conditions required for evaluating molecular geometries by this technique, and the development of the LISA (lanthanide induced shift analysis) suite to take account of the diamagnetic shifts in a more complete analysis. Some illustrative examples of the use of this technique are given. The solution conformation of bicyclo [3,1,0] hexan-3-one was determined as a flattened boat conformation. The molecular geometries of a number of 4-substituted and 2,6-disubstituted benzaldehydes, acetophenones, and benzoates were deduced and considered with respect to theoretical studies. The results showed clearly that LIS can be used to directly test the molecular geometries. The solution conformations of some α,β-unsaturated carbonyl compounds (aldehydes, ketones, and esters) were investigated and the s-cis–s-trans conformer energies were obtained. The conformations of some aromatic SO compounds were obtained and compared with theoretical predictions. Also reference is given to the use of LIS in alcohols, lactones, quinolines, cyclic amines, 1,3-dioxanes, and epoxides.