The geometries of the reactant, products, and transition state of the title reaction have been optimized at UHF, UMP2, and UMP4 levels with the double and triple zeta basis sets as well as polarization functions using the energy gradient method. The best potential barrier height for this reaction was calculated to be 9.05kcal/mol with MP-SAC4 theory. The intrinsic reaction coordinate (IRC) was traced at UHF/6-3 1G and UMP2(FU)/6-311G** levels. The energy profile along the IRC was refined with subsequent MP-SAC4//MP2 calculations using UMP2(FU)/6-3 1 1G** geometries. The vibration modes and the couplings between the IRC and the normal modes were analyzed along the IRC. The calculated rate constants at the level of MP-SAC4//MP2 theory are in good agreement with the most recent experimental values in the temperature range from 2200 to 2800 K.

Density functional (B3LYP) calculations, using the 6-31G** basis set, have been employed to study the title reactions. For the model reaction (H2CdC-NH+dCH2 + H2CdCH2), a complex has been formed with 6.2kcal/mol of stabilization energy and the transition state is 4.0kcal/mol above this complex, but 2.1kcal/mol below the reactants. However, the substituent effects are quite remarkable. When ethene is substituted by electron-withdrawing group CN, the reaction could also yield sixmembered-ring products, but the energy barriers are all more than 7 kcal/mol, which shows that CN group unfavors the reaction. The other substituents, such as CH3O and CH3 groups, have also been considered in the present work, and the results show that they are favorable for the formation of six-membered-ring adducts. The calculated results have been rationalized with frontier orbital interaction and topological analysis.

The mechanisms of seven reactions between keteniminium cations and olefins have been theoretically explored at BHandHLYP/6-31G* level. It is found that these seven reactions always form a relatively stable hydrogen-bonded type of ion-molecule complex first except for reactions 1d+2a and 1e+2a, which have no hydrogen atom attached to nitrogen atom in keteniminium cations. Some reactions take place via a concerted but unsynchronous mechanism, and the others are stepwise processes. The substituent effects are also studied. The data reveal that the electronpushing substituents on keteniminium cations disfavor the reaction, and the electron-attracting substituents on keteniminium cations favor the reactions. The substituent effects on ethene are contrary to the former case.

Density functional (B3LYP) calculations using the 6-31++g** basis set have been employed to study the title reaction between the cationic 1,3-dipolar 1-aza-2-azoniaallene ion (H2CdN+dNH) and ethene. Our calculations confirmed that [3 + 2] cycloaddition reaction takes place via a threemembered ring intermediate. In addition, solvent effects and substituent effects were also studied. For the reactions involving tetrachloroethene, there are two attacking sites. One is on the NH group in the 1-aza-2-azoniaallene ion, another is on its terminal CH2 group, and they are competitive for both approaching positions. Electron-releasing methyl substituents on ethene favor the reaction, and the potential energy surface is quite different from the previous one.

This paper uses the properties of atom X enclosed within an adamantane cage, denoted by X@C10H16, as a vehicle to introduce the Ehrenfest force into the discussion of bonding, the properties being determined by the physics of an open system. This is the force acting on an atom in a molecule and determining the potential energy appearing in Slater's molecular virial theorem. The Ehrenfest force acting across the interatomic surface of a bonded pair atomssatoms linked by a bond pathsis attractive, each atom being drawn toward the other, and the associated surface virial that measures the contribution to the energy arising from the formation of the surface is stabilizing. It is the Ehrenfest force that determines the adhesive properties of surfaces. The endothermicity of formation for X=He or Ne is not a result of instabilities incurred in the interaction of X with the four methine carbons to which it is bonded, interactions that are stabilizing both in terms of the changes in the atomic energies and in the surface virials. The exothermicity for X=Be2+, B3+, and Al3+ is a consequence of the transfer of electron density from the hydrogen atoms to the carbon and X atoms, the exothermicity increasing with charge transfer despite an increase in the contained volume of X.