Path-dependent thermal rate constants: The case of the combustion reaction between methyl hexanoate and hydrogen atom

This work uses the multipath canonical variational theory with small curvature tunneling (MP-CVT/SCT) to calculate the thermal rate constants for the hydrogen abstraction reaction on the α carbon of methyl hexanoate by H-atom. In the conformational search, 233 indistinguishable conformers for MHEX and TSα were located. In the MP-CVT/SCT approach, the recrossing and quantum tunneling effects were incorporated into the rate constants by constructing the individual reaction paths from the jth transition state. The efficiency of truncation on the multistructural rovibrational partition functions and reactive paths and their impact on the thermal rate constants were also evaluated. The torsion over the ▪ group (ϕ5) produces unstable structures, and the reactive paths associated with them do not contribute to the magnitude of MP-CVT/SCT rate coefficients. Additionally, we concluded that rate constants generated from small sets of conformations have a precision of up to 90%, compared to considering all paths. [Display omitted] •Thermal rate constants for methyl hexanoate + H reaction.•Torsional flexibility of the MHEX and TSα generates 233 distinguishable conformations.•Torsion over the ▪ group leads to unstable structures.•Small sets of conformations produce accurate rate constants.