Correlations between hardness, electrostatic interactions, and thermodynamic parameters in the decomposition reactions of 3-buten-1-ol, 3-methoxy-1-propene, 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 (ΔG ≠) increase from compound 1 to compound 3. The variations of the calculated ΔG ≠ values can not be justified by the decrease of the calculated global hardness (η) differences between the ground and transition states structures (i.e., Δ[η(GS)−η(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 (ΔS ≠) values can not be justified by the decrease of Δ[η(GS)−η(TS)] parameter from compound 1 to compound 3. On the other hand, dipole moment differences between the ground and transition state structures [Δ(µ TS−µ GS)] decrease from compound 1 to compound 3. Therefore, the electrostatic model associated with the dipole–dipole interactions justifies the increase of the calculated ΔG ≠ values from compound 1 to compound 3. The correlations between ΔG ≠, Δ[η(GS)−η(TS)], (ΔS ≠), k(T), electrostatic model, and structural parameters have been investigated.