The molecular structures of some simple olefins and small ring compounds

Abstract

The structures of three simple olefins and three small ring compounds containing double bonds have been determined by electron diffraction, and the results discussed in terms of hyperconjugation, rehybridization, strain, and intramolecular repulsions. In Part I, the structures of propene, isobutene, and cis butene-2 are described. The single bonds in these molecules have a length of about 1.50 A, exhibiting about half the shortening found in single bonds adjacent to triple bonds. In Part II, an attempt is made to calculate the intramolecular repulsive energy of the methyl groups in cis butene-2, using intermolecular force constants. Parts III, IV, and V describe the structure determinations of methylenecyclopropane, 1,3-dimethylenecyclobutane, and 1-methyl-3-methylenecyclobutene. In each case, the single bonds adjacent to double bonds are found to be short. Part VI contains some further discussion of the factors which alter carbon-carbon single bond lengths.