Part II : ab initio and NMR investigations into the barrier to internal rotation of various oxo- and thio- analogues of 2-oxo-2H-chromen-7-yl dimethylcarbamates : research article

A range of 2-oxo-2H-chromen-7-yl dimethylcarbamates were synthesized as described in part I of this publication, containing either an oxygen or sulphur α to the carbonyl or thiocarbonyl group of the amide moiety. Variable temperature and exchange spectroscopy NMR was performed on these compounds and the barrier to free amide rotation was calculated. Each of these compounds were also modelled ab initio and the gas phase barrier to rotation calculated. These three sets of data were compared and the influence of the α-heteroatom on rotation for amides and thioamides evaluated.