Computational Studies of Intramolecular Hydrogen Atom Transfers in the β-Hydroxyethylperoxy and β-Hydroxyethoxy Radicals

Abstract

The -hydroxyethylperoxy (I) and -hydroxyethoxy (III) radicals are prototypes of species that can undergo hydrogen atom transfer across their intramolecular hydrogen bonds. These reactions may play an important role in both the atmosphere and in combustion systems. We have used density functional theory and composite electronic structure methods to predict the energetics of these reactions, RRKM/master equation simulations to model the kinetics of chemically activated I, and variational transition state theory (TST) to predict thermal rate constants for the 1,5-hydrogen shift in I (Reaction 1) and the 1,4-hydrogen shift in III (Reaction 2). Our multi-coefficient Gaussian-3 calculations predict that Reaction 1 has a barrier of 23.59 kcal/mol, and that Reaction 2 has a barrier of 22.71 kcal/mol. These predictions agree rather well with the MPW1K and BB1K density functional theory predictions but disagree with predictions based on B3LYP energies or geometries. Our RRKM/master equation simulations suggest that almost 50% of I undergoes a prompt hydrogen shift reaction at pressures up to 10 Torr, but the extent to which I is chemically activated is uncertain. For Reaction 1 at 298 K, the variational TST rate constant is ∼30% lower than the conventional TST result, and the microcanonical optimized multidimensional tunneling (µOMT) method predicts that tunneling accelerates the reaction by a factor of 3. TST calculations on Reaction 2 reveal no variational effect and a 298 K µOMT transmission coefficient of 10 5 . The Eckart method overestimates transmission coefficients for both reactions.

1,n‐Hydrogen‐Atom Transfer (HAT) Reactions in Which n≠5: An Updated Inventory

“…They involve mainly heteroatom‐centered radicals (X=O, N, less frequently S) or vinyl and aryl radicals (X=sp 2 C), but exothermic HAT to alkyl radicals are also known 7. Quantum chemistry and force‐field‐based calculations have been used to model HAT 8–11. It is currently accepted that the ideal arrangement of the three atoms involved in the transition state of intermolecular HAT is linear.…”

“…Reactions involving 1,4‐translocations on a preparative scale are rather scarce; they are often mentioned as unexpected side processes 11. 20 As an example Crich et al.…”

Theoretical model on the formation possibility of secondary organic aerosol from OH initialed oxidation reaction of styrene in the presence of O 2 /NO

“…The corresponding DE and DE P were calculated to be 18.53 and 19.05 kcal/mol, respectively. Nevertheless, the lowest barrier among the intramolecular hydrogen shift was at least 25e35 kcal/mol (Kuwata et al, 2007;Liu et al, 2009), indicating that this pathway can occur easily at ambient environment. Subsequently, IM1B could dissociate immediately to form recycled OH, HCHO, and benzaldehyde, given no barrier DE (0.99 kcal/mol) and high exothermic energy (À42.25 kcal/mol).…”

Spectroscopic studies of the $\tilde{A}$Ö$\tilde{X}$X̃ electronic spectrum of the β-hydroxyethylperoxy radical: Structure and dynamics

“…The ground state potential energy surface (PES) for the isomerization had been discussed previously, [20][21][22][23] and key results are summarized in Table II. Previously, the G2 calculation method has been used to predict the rotational constants and has achieved good agreement with experimental results, 4, 7 however, it is a laborious, manual process to calculate a first order saddle point using the procedure.…”

“…[20][21][22][23] The product of this migration is β-hydroperoxy ethoxy, β-HPE, which is also an important intermediate in atmospheric chemistry.…”