Energy decomposition analysis of cis and trans isomers of 1,2-dihaloethylenes and 2-butene

Mayer's energy decomposition method was applied inthe study of the relative stability of cis and trans isomers of 1,2-disubstituted ethylenes, XHCCHX (X = F, Cl, Br) and 2-butene. The trans to cis isomerization energy for each system was determined at the Hartree-Fock level, with several basis sets, and then divided into monoatomic and diatomic energy contributions. The results point to a different energy distribution for the dihaloethylenes, known for exhibiting a cis isomer that is more stable than the trans one, a behavior that is known as the cis effect, when compared to 2-butene. The main stabilizing effects of the cis isomer in the dihaloethylenes, at this level of theory, are energy terms associated with the interaction of the X substituents with the C atoms.