Theoretical studies on the substituent effect of the thermal cycloaddition of ethylene and formaldehyde

Abstract

Ab initio HF molecular orbital calculations using 3-21G and 6-31G ∗ basis sets and including electron correlation (MP2 to MP4) have been applied to investigate the concerted supra-antara [2 s + 2 a] thermal cycloaddition reaction of some substituted ethylenes and formaldehyde. The stepwise reaction paths have also been studied for one of the reactions by using UHF/3-21G and MP2/3-21G. The calculated results indicate that although the presence of some particular substituents can decrease the activation barriers obviously, the title reaction is difficult to carry out via the supra-antara [2 s + 2 a] thermal cycloaddition pathway under moderate conditions. However, the reactions are probably carried out via stepwise pathways when there are strong electron-withdrawing groups in formaldehyde and/or electron-releasing groups in ethylene.