Theoretical Study of the Electronic Structure and Rotational Isomerism of Bis-Substituted Acetylenes

Abstract

The existence of stable rotational isomers of bis-substituted acetylenes has been checked theoretically. The mutual rotation of π-donating or π-accepting substituents having C_2v or C_s local symmetry is characterized by the barriers up to 10 kJ mol⁻ and more according to HF SCF MO data (6–31G and 6–31G* basis sets). Two π-donors or two π-acceptors stipulate stable s-gauche conformation while the molecules with π-donating or π-accepting substituents are stable in s-cis or s-trans conformations.