The importance of non-axial symmetry in the interpretation of lanthanide-induced shifts for ketones

Abstract

Pr(dpm) 3-induced shifts in the PMR spectrum of camphor are significantly better explained if the McConnell-Robertson expression is extended to include a term with non-axial symmetry, which contributes between 1% and 40% to the individual shifts. Complexes of six other ketones provide further evidence. Good agreement with observed shifts was obtained without any optimisation of lanthanide-oxygen bond lengths or angles. The success of the extended expression suggests that complexes of ketones with shift reagents may exist in two preferred rotational conformations.