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Rhodium-catalyzed cycloaddition reaction was calculated by density functional theory M06-2X method to directly synthesize benzoxepine and coumarin derivatives. In this work, we conducted a computational study of two competitive mechanisms in which the carbon atom of acetylene or carbon monoxide attacked and inserted from two different directions of the six-membered ring reactant to clarify the principle characteristics of this transformation. The calculation results reveal that: (i) the insertion process of alkyne or carbon monoxide is the key step of the reaction; (ii) for the (5+2) cycloaddition reaction of acetylene, higher energy is required to break the Rh−O bond of the reactant, and the reaction tends to complete the insertion from the side of the Rh−C bond; (iii) for the (5+1) cycloaddition of carbon monoxide, both reaction paths have lower activation free energy, and the two will generate a competition mechanism. [ABSTRACT FROM AUTHOR]

Abstract: A computational study of the [2+2] cycloaddition reaction pathways for formaldehyde–ketene and formaldehyde–isocyanic acid has been presented by using the DFT(B3LYP) method. These cycloaddition reactions could yield to eight different four-membered molecules. In the two considered reactions, the reactions for the β-propiolactone and oxazetidinone products have the lower barriers of 26.40 and 32.88kcalmol−1 and are exothermic by 27.68 and 4.00kcalmol−1, respectively. The β-propiolactone and oxazetidinone ring compounds have been predicted to be the most stable thermodynamically. Simulation of the solvent environment (toluene, THF, acetone, acetonitrile and water) has been investigated by using polarized continuum model method, yet only small differences have been found to occur in energetics between the studied structures in the gas-phase and in the solvent. [Copyright &y& Elsevier]

Abstract: In order to explore the new and efficient cyclopropanation reagents, a theoretical investigation of the cyclopropanation reactions of aluminum carbenoid Cl2AlCH2Cl with olefins was given at the B3LYP level of theory. All of the reactions examined displayed similar concerted mechanisms for the cyclopropanation of these reagents. The reactions are predicted to be highly chemical reactivity with low barriers and could be favored in experiment, and the cyclopropanation reaction proceed easily at lower temperature. The computational results are briefly compared to other carbenoid reactions and related species. [Copyright &y& Elsevier]

Abstract: In order to explore the new and efficient cyclopropanation reagents, a theoretical investigation of the cyclopropanation reactions of titanium carbenoid PhOTiCl2CH2Cl and Cl3TiCH2Cl with olefins was given at the B3LYP level of theory. All of the reactions examined displayed similar concerted mechanisms for the cyclopropanation of these reagents. The reactions are predicted to be highly chemical reactivity with low barriers and could be favored in experiment, and the cyclopropanation reaction proceed easily at lower temperature. The computational results are briefly compared to other carbenoid reactions and related species. [Copyright &y& Elsevier]

Abstract: A computational study of methane to methanethiol Conversion by first-row transition-metal sulfide ion reactions of MnS+ with CH4 is presented. The reaction proceeds through two competing pathways: pathway A via intermediate formation of CH3MnSH+ (IM2). The second pathway, which leads to the insertion isomer HMnSCH3 + (IM4). Both pathway barriers to reactions become systematically lower as quintet state system(47.52 and 67.66 kJmol−1 for pathway A and pathway B, respectively). In contrast, the reaction barriers for septet state via both pathway remain high (>125kJmol−1). Mn+ and MnSH+ are formed as major ionic products in the reaction of MnS+ with CH4, The computational results are briefly compared to other reactions and related species. [Copyright &y& Elsevier]

Abstract: The mechanisms for the abstraction reactions of germylenes with oxirane and thiirane have been characterized in detail using density functional theory. All the stationary points were determined at the B3LYP/6-311++G (d, p) level of the theory. As a result, our theoretical investigations suggest that, irrespective of deoxygenation and desulfurization, the alkyl-substituted germylene abstractions are much more favorable than those of the π-donor-substituted germylenes. Moreover, for a given germylene, the desulfurization reaction is more exothermic as well as more kinetically favorable. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. A comparison with carbene and silylene also led to the same result and the results obtained allowed a number of predictions to be made. [Copyright &y& Elsevier]