The specific effect of oxygen lone pairs on the trans CH vibrator, previously noted in dimethyl ether, has been observed in 1,3-dioxolane(D 5) and 1,3-dioxane(D 7). This interaction allows us to determine the conformation of some other compounds with the —OCHRO— group. In 2-methyl and 2-trichloromethyl-1,3-dioxolane, the R group is in an essentially pseudoequatorial position; in 2-ethynyl-1,3-dioxolane, an equilibrium between the two isomers is observed, the isomer with the pseudoaxial R group is more favored in solvent CCl 4 than in solvent CD 3CN. In dimethoxymethane, the gauche—gauche isomer predominates; although other forms appear in 1,1-dimethoxyethane the gauche—gauche isomer is still preferred. In trimethoxymethane, the existence of the two isomers TGG and TGG' has been confirmed. These results complete those previously obtained, essentially from the analysis of NMR spectra of the non-deuterated compounds.