Conformational equilibria of 7-benzyl-2-iodo-9-oxa-7-azabicyclo[4.3.0]nonan-8-one in solution. Correlations between conformational distribution and solvent solvatochromic parameters.

A quantitative study of the variation of the conformational equilibria of 7-benzyl-2-iodo-9-oxa-7-azabicyclo[4.3.0]nonan-8-one 1 in 10 solvents has been carried out. The experimental composition in each solvent has been obtained from experimental NMR vicinal H-H coupling constants together with molecular modeling. The solvent properties, particularly polarity and hydrogen bonding ability, were described according to Kamlet and Taft using experimental parameters. Very good linear relationships were obtained between the equilibrium constants of each single conformational equilibrium and the polarity and hydrogen bonding parameters of the solvent. These linear relationships allow an accurate prediction of the conformational composition in any solvent as well as a thorough understanding of the influence of each separate parameter on the conformational equilibrium composition.