Steric structure of 4-, 4,6-, and 4,4,6-methyl-substituted 2,2-diphenyl-1,3-dioxa-2-germacyclohexane according to PMR data

In the spectrum of 4,4,6-trimethyl-2,2-diphenyl-1,3-dioxa-2-germacyclohexane, according to an analysis of the ABX spin system with additional splitting on account of methyl groups, a geminal coupling constant of 14.2 Hz and vicinal constants characteristic for axial-axial and axial-equatorial interactions of protons in the chair conformation /sup 3/J(H/sup ..lambda../H/sup ..cap alpha../) 9.7, /sup 3/J(H/sup ..lambda../H/sup e/) 2.8 Hz are observed. A chair conformation is also indicated by the reversal of the chemical shifts of the protons on the C/sup 5/ atom equatorial proton resonates in a higher field than the axial proton) (8). Also, the protons of the methyl groups on the C/sup 4/ atom give a singlet in the spectrum, which may indicate the realization of a conformation differing from the chair form or the accidental isochronism of the methyl groups. The recording of the spectrum of this compound in C/sub 6/H/sub 6/ leads to the anisochronism of the two methyl groups and the appearance of two signals.