Abstract: Proton NMR spectroscopy and X-ray crystallographic studies demonstrate the predominance of the axial conformer of 2-(diphenylphosphinoyl)-l, 3-dithiane (1). Chemical equilibration of anancomeric models (2~ i 3) allows quantitative determination of the conformational free energy in 1, 1.0 kcal/mol, which corresponds to an anomeric effect of 3.74 kcal/mol, the largest yet measured. Comparison of the structural data for 1-ax and 2 ( ...
