Aluminirene (HAlC2H2) and aluminirane (HAlC2H4): aluminum-substituted counterparts of cyclopropene and cyclopropane

The theoretical molecular structures, energetics, and vibrational frequencies of isomers of HAl-acetylene and HAl-ethylene have been predicted by ab initio quantum mechanical methods. Standard double-{zeta} plus polarization (DZ+P) basis sets, triple-{zeta} plus polarization (TZ+P), and triple-{zeta} plus double polarization (TZ+2P) basis sets have been used for full geometry optimizations in conjunction with self-consistent-field (SCF) and single and double excitation configuration interaction (CISD) methods. The predictions are in good agreement among the different theoretical methods. The TZ+P CISD dissociation energies of AlC{sub 2}H{sub 3} with respect to AlH + C{sub 2}H{sub 2} were found to be 27.7 kcal/mol for the aluminirene ring structure, while H{sub 2}AlC{double bond}CH and :AlCH{double bond}CH{sub 2} are more stable by 14.4 and 19.8 kcal/mol, respectively. Similarly the dissociation of AlC{sub 2}H{sub 5} to AlH + C{sub 2}H{sub 4} is endothermic by 6.9 kcal/mol for the aluminirane ring structure, while H{sub 2}AlCH{double bond}CH{sub 2} and :AlCH{sub 2}CH{sub 3} are more stable by 21.4 and 26.1 kcal/mol, respectively.