'Objective' determination of coupling constants and conformational equilibria by solvent variation: a comment.
Following the preceding paper, the 'objective' method of Abraham et al. for determining the conformational equilibrium between molecules rapidly interconverting between a number of different conformers has been re-evaluated. The method relies on the acquisition of a sufficient data set of nuclear couplings in different solvents to obtain an over-determined system with more equations than unknowns. The example considered by Deutsch and Roberts, of 1,2-dichloro-1-fluoroethane, is re-evaluated here. A simple but mathematically rigorous computer scanning process is used to analyse the data set instead of the iterative but not mathematically rigorous process used previously and the results compared with those of Deutsch and Roberts. It is shown that both treatments give similar solutions. However, it is emphasized that in these multi-dimensional analyses the probable errors in the derived parameters (in this case the conformer couplings) may be much larger than the r.m.s. (observed versus calculated) errors and this error analysis is essential for a considered appraisal of the method.
Abraham
Raymond J
RJ
Chemistry Department, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK. abrahamr@liv.ac.uk