The Molecular Structures of Glyoxal and Dimethylglyoxal by the Electron Diffraction Method

Abstract

Extension to open chain heteroatomic aliphatic compounds of the structural investigations of the constitutional effect of different bonds upon adjacent bonds should provide useful information concerning the electronic structures and the extent of resonance in these molecules. The recent electron diffraction studies of formaldehyde and acetaldehyde have given a reliable value for the carbon-oxygen double bond distance. We have now extended the investigation of compounds containing the carbonyl group to glyoxal and dimethylglyoxal, both of which contain a pair of conjugated carbon-oxygen double bonds and present the possibility of free rotation around the carbon-carbon bond connecting the adjacent carbonyl groups. Furthermore, both substances are colored, glyoxal being the simplest colored compound whose molecules have a conjugated system. Of the compounds glyoxal, dimethylglyoxal, oxalyl chloride, oxamide, and oxalic acid, it is found that glyoxal and dimethylglyoxal are colored whereas the remaining compounds are colorless. All five of these compounds may be represented by the formula RCORCO and the difference in color between the first two compounds and the remaining three compounds suggests that there may be a structural difference between the two groups of compounds. Oxalyl chloride is now under investigation in these Laboratories by the electron diffraction method, and the X-ray study of crystals of oxamide is also under way.