Studies on Cyclitols. XIV. Methyl Group Signals ofgem-Dimethyldioxolanes as Indicators of Anisotropy

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Abstract
In connection with our interest in nmr spectroscopy of cyclopentanoid and 2, 4-dioxabicyclo[3. 3. 0] octane systems3 we have synthesized a large number of gem-dimethyldioxolanes2,4 and have examined their spectra. The spectra of all the compounds showed two distinct singlets, representing the two methyl groups, in the region δ 1. 2-1. 5. Similar values have been reported in the case of derivatives of 1, 2-O-isopropylidene-α-D-xylohexofuranose by Abraham et al.5 Perlin6 has reported similar differences in the chemical shift of the endo- and exo- C-methyl groups of the diastereoisomeric orthoacetates of D-mannose, and Baggett et al.7 observed a difference of 0. 30 ppm between the chemical shifts of endo- and exo-benzyl protons of O-benzylidene sugars. Our studies permit the assignment of the lower field resonance to the endo-methyl group and the higher field resonance to the exo-methyl group of the dimethyldioxolanes.