Conformational Analysis. 46. Conformational Equilibria in 3-Hydroxy-, 3-Methoxy-, and 3-Acetoxythianes, Their Sulfoxides and Sulfones, and Some Corresponding 3-Methyl Homologues

Article abstract of DOI:10.1021/jo00355a018

Conformational equilibria have been measured, by low-temperature carbon-13 and proton NMR spectroscopy, for 3-hydroxythiane, its two epimeric sulfoxides, and the corresponding sulfone and their methyl ethers and acetates, as well as the corresponding derivatives of 3-methyl-3-hydroxythiane and their acetates.Of particular note are large solvent and concentration effects on the conformational free energies, ΔG⁰_a<*>e, especially in cases where intramolecular and intermolecular hydrogen bonding are competitive.Thus, in 3-hydroxythiane, ΔG⁰ rises from -1.20 kcal/mol in 4 M CD2Cl2 to -0.22 kcal/mol in 0.0011 M CD2Cl2; for the corresponding cis sulfoxide the rise is from < -1.3 kcal/mol in 0.3 M CD3OD to -1.0 kcal/mol in 2.8 M CD2Cl2 to > +1.3 kcal/mol in 0.0023 M CD2Cl2 and in the sulfone it is from < -1.3 kcal/mol in 0.3 M CD3COCD3 to -0.9 kcal/mol in 0.3 M CD2Cl2 to -0.16 kcal/mol in 0.002 M CD2Cl2.