Molecular insights into the dehydration mechanism of 1,2-butanediol: A CBS-QB3 and G4MP2 study.

contextThe present work provides a detailed theoretical investigation of the full dehydration mechanism of 1,2-butanediol (1,2-BDO) using Complete Basis Set-Quadratic Becke3 (CBS-QB3) and Gaussian-4 Møller-Plesset perturbation theory (G4MP2) methods. Bond dissociation energy (BDE) analysis revealed distinct differences between the two hydroxyl groups in 1,2-BDO. The terminal C1-O1 bond is weaker than the internal C2-O2 bond by 1.7 and 1.9 kcal mol⁻

methodsThe dehydration mechanism of 1,2-BDO was investigated using the composite ab initio CBS-QB3 and G4MP2 computational methods. The CBS-QB3 approach involves geometry optimization and vibrational frequency calculations at the B3LYP/6-311G(d,p) level, followed by higher-level single-point energy calculations incorporating CCSD(T), MP4SDQ, and MP2 corrections, together with complete-basis-set (CBS) extrapolation to enhance the accuracy of the calculated energies. In the G4MP2 approach, molecular geometries and vibrational frequencies are optimized at the B3LYP/6-31G(2df,p) level, followed by a series of higher-level single-point calculations using CCSD(T,FC)/6-31G(d), MP2(FC)/G3MP2LargeXP, RHF/mod-aug-cc-pVTZ, and RHF/mod-aug-cc-pVQZ levels. Fundamental thermochemical properties, including atomization enthalpies (AE), bond dissociation energies (BDEs), ionization energies (IEs), and electron affinities (EAs), were calculated for 1,2-BDO and the species involved in its decomposition. The reliability of the computational methods was evaluated by comparing the calculated results with available theoretical and experimental data. BDE analysis was used to assess the relative strength and reactivity of the two hydroxyl groups, while thermodynamic analyses were applied to compare the 19 proposed dehydration pathways.