Conformational Structure of Molecules with Weakly Hindered Internal Rotation

The torsion potentials of divinylacetylene (1) and 1,4-dichlorobutyne (2) were calculated by the HF/6-31G* method. It is found that the barrier of internal rotation is 164 cm^-1 for 1 and 214 and 29 cm^-1 for the cis- and trans-conformations of 2, respectively. The energies and the wave functions of the torsion states were calculated by solving the Schrödinger equation. The distribution of molecules 1 and 2 over torsion angle was determined at different temperatures.