The potential energy surface involved in the thermal decomposition of 1-propanol radicals was investigated in detail using automated codes (tsscds2018 and Q2DTor). From the predicted elementary reactions, a relevant reaction network was constructed to study the decomposition at temperatures in the range 1000-2000 K. Specifically, this relevant network comprises 18 conformational reaction channels (CRCs), which in general exhibit a large wealth of conformers of reactants and transition states. Rate constants for all the CRCs were calculated using two approaches within the formulation of variational transition-state theory (VTST), as incorporated in the TheRa program. The simplest, one-well (1W) approach considers only the most stable conformer of the reactant and that of the transition state. In the second, more accurate approach, contributions from all the reactant and transition-state conformers are taken into account using the multipath (MP) formulation of VTST. In addition, kinetic Monte Carlo (KMC) simulations were performed to compute product branching ratios. The results show significant differences between the values of the rate constants calculated with the two VTST approaches. In addition, the KMC simulations carried out with the two sets of rate constants indicate that, depending on the radical considered as reactant, the 1W and the MP approaches may display different qualitative pictures of the whole decomposition process.

The photochemistry of a model merocyanine-spiropyran system was analyzed theoretically at the MS-CASPT2//SA-CASSCF(14,12) level. Several excited singlet states were studied in both the closed spiropyran and open merocyanine forms, and the paths to the different S(1)/S(0) conical intersections found were analyzed. After absorption of UV light from the spiropyran form, there are two possible ultrafast routes to efficient conversion to the ground state; one involves the rupture of the C(spiro)-O bond leading to the open form and the other involves the lengthening of the C(spiro)-N bond with no photoreaction. From the merocyanine side the excited state can reach a very broad S(1)/S(0) conical intersection region that leads the system to the closed form after rotation of the central methine bond. Alternatively, rotation of the other methine bonds connects the system through different S(1)/S(0) conical intersections to several merocyanine isomers. The present work provides a theoretical framework for the recent experimental results (Buback , J. J. Am. Chem. Soc. 2010, 132, 1610-1619) and sheds light on the complex photochemistry of these kinds of compounds.

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The reactant cluster and transition state for epoxidation of allyl alcohol with peroxyformic acid have been located at the MP2/6-31G(d) level of theory. The free energy of activation (Δ = 19.8 kcal/mol) predicted at the MP4//MP2/6-31G(d) level is quite comparable with experimental data for epoxidation of 3-hydroxycyclohexene (Δ = 19.7 kcal/mol). A spiro transition state (TS) was found where the plane defined by the peroxyacid moiety is oriented at 89° to the CC bond axis. Intrinsic reaction coordinate analysis suggests that after the barrier is crossed a 1,4-hydrogen migration of the peroxyacid hydrogen to the carbonyl oxygen takes place in concert with O−O bond cleavage affording the epoxide of allyl alcohol hydrogen bonded to the neutral formic acid leaving group. The activation parameters calculated at the B3LYP/6-311G(d,p) level are in excellent agreement with the MP4//MP2 values. The transition structure with the allyl alcohol O−C−CC dihedral angle of 16.4° is 2.1 kcal/mol lower in energy than a transition structure with a dihedral angle of 134.3°. The directing effect of the hydroxyl group is attributed initially to a primary hydrogen bonding interaction between the relatively more acidic peroxy acid proton and the oxygen of the allyl alcohol. In both the reactant complex 1 and the transition structure (TS-2) for oxygen atom transfer the alcohol remains hydrogen bonded to the more basic carbonyl oxygen of the peroxyacid. The G2 proton affinities (PA298) of the carbonyl oxygen and the proximal peroxo oxygen of peroxyformic acid are 177.1 and 153.3 kcal/mol, respectively.