Performance of simplified G2 model chemistry approaches in the study of unimolecular mechanisms: thermal decomposition of acetic acid in gas phase

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Ab initio calculations of equilibrium structures and transition states for decarboxylation and dehydration mechanisms of gas phase pyrolysis of acetic acid are put forward. The accuracy and efficiency of different G2-based methods are compared, namely G2(MP2), G2(MP2,SVP)/B3-LYP and G2/CASSCF10-in-10 of Duan and Page. The theoretical activation energies obtained using these three methods are very close to the experimental ones and the optimized equilibrium structures at B3-LYP, MP2 and CASSCF/6-31G(d) levels are very similar. However, the computational effort is reduced for the G2 (MP2,SVP)/B3-LYP calculation without any accuracy loss.