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Structures, Rotational Barriers, and Thermochemical Properties of Chlorinated Aldehydes and the Corresponding Acetyl (CCO) and Formyl Methyl Radicals (CCO) and Additivity Groups

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journal contribution
posted on 15.12.2001, 00:00 by Li Zhu, Joseph W. Bozzelli
Chlorinated formyl methyl radicals (CCO) are the stable keto forms of chlorovinoxy radicals formed by cleavage or abstraction of the weak O−H bonds of chlorovinyl alcohols. Thermochemical properties, ΔHf°298, S°298, and Cp°(T) (5 K ≤ T ≤ 6000 K), are computed by density functional B3LYP/6-31G(d,p) and B3LYP/6-311+G(3df,2p), ab initio QCISD(T)/6-31G(d,p), and composite CBS-Q calculation methods for chlorinated aldehydes and the corresponding chlorinated acetyl and formyl methyl radicals:  CH3CHO (1), CH3CClO (2), CH2ClCHO (3), CH2ClCClO (4), CHCl2CHO (5), CHCl2CClO (6), CCl3CHO (7), CCl3CClO (8), CH3CO (9), CH2ClCO (10), CHCl2CO (11), CCl3CO (12), CH2CHO (13), CH2CClO (14), E-CHClCHO (15), Z-CHClCHO (16), CCl2CHO (17), E-CHClCClO (18), Z-CHClCClO (19), CCl2CClO (20). Molecular structures and vibration frequencies are determined at the B3LYP/6-31G(d,p) level of theory. Vibration frequencies are scaled for zero-point energies and thermal corrections. Two to four isodesmic reactions are utilized at each calculation level to determine ΔHf°298 of each species. Contributions to S°298 and Cp°(T) from translation, vibration, and external rotations are calculated using the rigid-rotor-harmonic-oscillator approximation based on the B3LYP/6-31G(d,p) structures. Hindered internal rotational contributions to entropies and heat capacities are calculated by summation over the energy levels obtained from direct diagonalizations of the Hamiltonian matrix of the internal rotation. The bond energies of C−H and C−Cl in chloroaldehydes are also calculated.