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 ( ...