The vibration spectrum and molecular configuration of 1:4-dioxane

The symmetry properties and selection rules for the normal vibrations of 1:4-dioxane have been derived for all possible symmetries of the molecule. The numbers of frequencies observed in the infra-red spectrum of the vapour and Raman spectrum of the liquid are shown to be inconsistent with structures of low symmetry. While the number of observed Raman frequencies do not distinguish between the ‘chair’ and planar configurations, the number of observed infra-red frequencies slightly favours the ‘chair’ structure. The twelve vibration frequencies of the ring have been calculated for the ‘chair’ structure using a simple valency force field with four force constants. Seven of the calculated frequencies agree with the observed frequencies to within 1%, and two frequencies agree to within 3 to 4%. Of the three remaining frequencies, two are active in the infra-red spectrum but are too low to be observed with prism spectrometers, while the third is active in the Raman spectrum but has not been experimentally observed. These three frequencies, however, agree satisfactorily with the corresponding assignments for cyclohexane. The stretching constants of the C-C and C-O bonds, viz. 3.7 x 10 5 and 4.45 x 10 5 dynes/cm., were found to be the same as for cyclohexane and dimethyl ether respectively.