This paper reports a theoretical study, at the B3LYP/6-31 R G(d,p) and M05-2X/6-31G R (d,p) levels, on the thermal decomposition of menthyl benzoate (2-isopropyl-5-methylcyclohexyl benzoate). It undergoes a unimolecular first-order elimination to give 3-menthene (1-isopropyl-4-methylcyclohexene), 2-menthene (3-isopropyl-6-methylcyclohexene), and benzoic acid. We studied two possible mechanisms trying to explain the formation of 2-and 3-menthene, via six-membered or four-membered cyclic transition states. Rate constants were calculated at two temperatures, 587.1 and 598.6 K, and they agree well with the experimentally determined values. We verify that 3-menthene is the product mainly formed at both temperatures. The progress of the reactions has been followed by means of the Wiberg bond indices. Intrinsic reaction coordinate (IRC) calculations have been carried out to verify that the localized transition state structures connect with the reactants and products and also to verify that the parent compound, menthyl benzoate, is taking the cis-configuration needed in the reaction. a Values calculated using 6-31þG(d,p) basis set. b A scaling factor [26] of 0.9804 for ZPE has been used. c Values taken from ref [6] .

In this paper we report the geometries and properties of 40 structural isomers located on the MP2/6-311++G** PES of the carbonic acid dimer. All six possible combinations of carbonic acid monomers were considered. The dimers are divided into six geometrical motifs. Our data suggests that combinations of anti-anti monomers do not necessarily lead to larger stabilization energies in the formation of the dimers. MP2 underestimates the relative binding energies with respect to CCSD(T) by as much as 3.2 kcal mol(-1). At least 3 different dimers which may contribute to the stability of carbonic acid are predicted to have significant populations. Binding energy is only directly related to relative stability when comparing dimers formed from the same monomers. Overall stabilization is mainly dictated by attractive electrostatic interactions via cooperative polarization by virtue of the spatial arrangement of the dipole moment components along the polar bonds. Shorter OH bond distances and larger bond orders predicted for the hydrogen bonds directed towards carbonyl groups make for stronger hydrogen bonding than in O...H bonds directed towards hydroxyl groups.

A theoretical study on the mechanism of the thermal decomposition of a series of xanthates, O‐alkyl S‐methyl and S‐alkyl O‐methyl dithiocarbonates, has been carried out, and the alkyl groups being ethyl, isopropyl, and tert‐butyl. Kinetically, these xanthates can be classified in two groups: those where the oxygen atom is involved in the bonding changes of the transition state (properly the Chugaev reaction), and those where it is not, O‐alkyl S‐methyl and S‐alkyl O‐methyl dithiocarbonates, respectively. We have studied not only the thermal elimination reactions but also the other possible reactions such as the thione‐to‐thiol rearrangement and the nucleophilic substitution to give ethers or thioethers. Two possible mechanisms for the thermal elimination reactions, in one and in two steps, respectively, have been studied. Calculations were made at the MP2/6‐31G(d) level of theory, and the progress of the reactions has been followed by means of the Wiberg bond indices. Copyright © 2008 John Wiley & Sons, Ltd.

The mechanism of thermal decomposition of 4-hydroxy-2-butanone in m-xylene solution was studied experimentally and theoretically at the M05-2X/6-31G(d , p) level of theory. It follows first-order kinetics and appears to be homogeneous and unimolecular. The proposed mechanism is via a six-membered cyclic transition state to give a mixture of formaldehyde and acetone. Rate constant values were experimentally determined at three temperatures: 483.15, 493.15, and 503.15 K. Calculated rate constants are of the same order of magnitude than the experimental ones. Calculated Gibbs energies of activation agree very well with the experimental values. Computationally, the progress of the reactions was followed by means of the Wiberg bond index. The results indicate that the transition state has an intermediate character between reactants and products, and the calculated synchronicity shows that the reaction is slightly asynchronous. The bond-breaking processes are more advanced than the bond-forming ones, indicating a bond deficiency in the transition state.