Ab initio electronic structure calculations and variational transition state theory are used to calculate reaction energetics and rate constants for the gas-phase reactions of OH- with CH(4 - n )Cl n for n = 1−4. Two reaction pathways are considered, second-order (bimolecular) nucleophilic substitution (SN2), and proton transfer. Benchmark electronic structure calculations using CCSD(T) and basis sets as large as aug-cc-pVQZ are performed to obtain highly accurate estimates of the enthalpies of reaction. These results are extrapolated to the complete basis set limit for comparison with experiment and to establish the level of theory needed to provide energies that are accurate to better than a few kJ/mol. Energies of critical geometries (reactant complexes, saddle points, and product complexes) are computed for all systems. For the SN2 reaction, the potential energy and its first and second derivatives along minimum energy paths are computed and used directly in variational transition state theory (VTST) calculations of the rate constants. These calculations indicate that for n = 1−3 the region of the potential in the asymptotic reactant channel controls the reaction rate constants and that the loose-transition-state methods implemented in variflex provide the best estimates of the reaction rate constants. The reaction with n = 4 has a dynamical bottleneck that lies near the saddle point and is best treated using the VTST methods implemented in polyrate.

Photochemical properties of a series of bifunctional monosubstituted derivatives of cymantrene containing a C-, N-, or O-bound π-allyl group, along with n-donating carbamate, amide, or pyridine fragments were investigated. The results obtained demonstrate that the nature and thermodynamic stability of the cyclopentadienylmanganese dicarbonyl chelates derived from bifunctional monosubstituted cymantrene derivatives depend substantially on both the nature of the functional groups and on their position in the substituent at the Cp ring. Thus, for the six-membered chelates, the thermodynamic stability increases in the series carbamates < amides < pyridines < olefins. Some of the dicarbonyl chelates studied form reversible photochromic systems due to linkage isomerization between different donating groups of the bifunctional substituent and the manganese atom with a wide range of times of thermal isomerization.

This study utilizes ab initio calculations to investigate the reaction of high-temperature solid-state catalytic isotope exchange (HSCIE) between amino acids and spillover tritium. The Hartree−Fock approximation and second-order Møller−Plesset perturbation theory in conjunction with 6-31G* and aug-cc-pVDZ basis sets were used to calculate potential energy surfaces for the interactions between CH4, alanine, hydroxyproline, and the H3O+ ion. Ab initio calculations were used to estimate the activation energies and structures of the transition states of these reactions. The hydrogen exchange reaction occurs by a synchronous mechanism, with a transition state that is characterized by pentacoordinated carbon. The proposed one-center mechanism is in good agreement with observed retention of configuration of the asymmetric carbon atoms in the HSCIE reaction with spillover tritium in experiments. The regioselectivity and stereoselectivity of hydrogen isotope exchange in amino acids with spillover tritium can be predicted on the basis of ab initio calculations of interaction of this compound with a model acidic center, taking the H3O+ ion as an example.

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