Effect of Substituents on Methylenecyclobutane / 1-Methylcyclobutene System
Ghassab M. Al-Mazaideh *
Department of Chemistry and Chemical Technology, Faculty of Science, Tafila Technical University, P.O.Box 179, Tafila 66110, Jordan
Rabia A. Enwisry
Department of Chemistry, School of Basic Science, Libyan Academy for Graduate Studies, P.O.Box 17979031, Tripoli, Libya
Salim M. Khalil
Department of Chemistry and Chemical Technology, Faculty of Science, Tafila Technical University, P.O.Box 179, Tafila 66110, Jordan
*Author to whom correspondence should be addressed.
Abstract
A theoretical study was performed on the methylenecyclobutane and 1-methylcyclobutene in the gas and aqueous phases using PM3 and DFT calculations. Methylenecyclobutane was found to be more stable than 1-methylcyclobutene in the gas and aqueous phases according to PM3 calculations, and only slightly more stable than 1-methylcyclobutene in the case of DFT calculations. Also the effect of substituents (X = F, CH3, NH2, CN, NO2, CHO and CF3) was studied on the relative stabilities of these two tautomers. It was found that all the substituents increase the stability of 1-methylcyclobutene in the gas and aqueous phases. Heats of formation, and electron densities, were reported. The stability effect of X- substituents on the methylenecyclobutane and 1-methylcyclobutene was explained by Gibbs free energies calculations and confirmed by isodesmic reactions.
Keywords: Cyclic alkene, tautomerism, PM3, DFT, substituents