computationally, to see if suitable substituents might be capable of increasing the isotope effect, and hence of the level of deuterium enrichment. The combination of experimental and theoretical results had led Giagou and Meyer to conclude that the system may exhibit significant deviations from transition state theory, 9 which if correct would mean using a level of computational modelling which goes beyond such theory to ensure that the models do correctly predict isotope effects for new variations of the Swern reaction bearing as yet unstudied substituents. Scheme 1. R=H.