The molecular conformations of 8,11-dimethyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin and 4,4-dimethyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin

Abstract

The conformational properties of 8,11-dimethyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin (5) and of 4,4-dimethyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin (6) have been investigated using 1H and 13C dnmr as well as ir spectroscopy. Analysis of low temperature nmr spectra (down to −148 °C) and of S=O stretching vibrations in room temperature ir spectra indicates that the most stable conformations detected for solutions in CHF2Cl/CD2Cl2 (80:20) are TB (83%) and C-a (17%) for 5 and only the TB 7 for 6. Substituent effects of methyl groups at the peri and the benzylic positions on the conformational properties of the seven-membered sulfites are discussed.