Correlations Between Hardness, Electrostatic Interactions, and Thermodynamic Parameters in the Decomposition Reactions of 3-Buten 3-Methoxy and Ethoxyethene

Abstract

Decomposition of the three isomeric compounds, 3-buten-1-ol (1), 3-methoxy-1-propene (2), and ethoxyethene (3), at two different (300 and 550 K) temperatures has been investigated by means of ab initio molecular orbital theory (MP2/6-311+G**//B3LYP/6-311+G**), hybrid-density functional theory (B3LYP/6-311+G**), the complete basis set, nuclear magnetic resonance analysis, and the electrostatic model associated with the dipole-dipole interactions. All three levels of theory showed that the calculated Gibbs free energy differences between the transition and ground state structures (Delta G (not equal)) increase from compound 1 to compound 3. The variations of the calculated Delta G (not equal) values can not be justified by the decrease of the calculated global hardness (eta) differences between the ground and transition states structures (i.e., Delta[eta(GS)-eta(TS)]). Based on the synchronicity indices, the transition state structures of compounds 1-3 involve synchronous aromatic transition structures, but there is no significant difference between their calculated synchronicity indices. The optimized geometries for the transition state structures of the decomposition reactions of compounds 1-3 consist in chair-like six-membered rings. The variation of the calculated activation entropy (Delta S (not equal)) values can not be justified by the decrease of Delta[eta(GS)-eta(TS)] parameter from compound 1 to compound 3. On the other hand, dipole moment differences between the ground and transition state structures [Delta(A mu (TS)-A mu (GS))] decrease from compound 1 to compound 3. Therefore, the electrostatic model associated with the dipole-dipole interactions justifies the increase of the calculated Delta G (not equal) values from compound 1 to compound 3. The correlations between Delta G (not equal), Delta[eta(GS)-eta(TS)], (Delta S (not equal)), k(T), electrostatic model, and structural parameters have been investigated.