STRUCTURES AND CONFORMATIONS OF CYCLOHEXADIENES

The structures of 1,3-cyclohexadiene and 1,4-cyclohexadiene in the gas phase were determined by electron diffraction. Interatomic distances and mean-square amplitudes of vibration were evaluated. In neither molecule are the carbon atoms coplanar; the structure found for the 1,3 isomer is in good agreement with the available microwave data. Of particular interest was the magnitude of the dihedral angle in the 1,4 isomer; it was found to be 159.3°. Here the copolanar conformation was expected from estimates of nonbonded repulsions. This pair of isomers provides critical test structures for the several sets of empirically parametrized potential functions proposed for calculating strain energies of cyclic hydrocarbons. © 1969, American Chemical Society. All rights reserved.