Theoretical investigation on isomerization and decomposition reactions of pentanol radicals-part I: branched pentanol isomers.

Abstract

Theoretical investigations on the kinetics of decomposition and isomerization reactions for five types of branched pentanol radicals are carried out in this work. The M06-2X/6-311++G(d,p) level of theory was used to optimize the geometries of all reactants, transition states, and products, while the hindrance potentials for the lower frequency modes in all of the species were obtained through a relaxed scan with an increment of 10° at the M06-2X/6-31G level of theory. Single-point energies of all species were determined at the QCISD(T)/cc-pVDZ, TZ level of theories with basis set corrections from MP2/cc-pVDZ, TZ, QZ methods. The RRKM/master equation was solved to calculate the pressure- and temperature-dependent rate coefficients for all channels in the pressure range of 0.01-100 atm over 250-2000 K. Pressure and temperature-dependent branching fractions of key species produced from pentanol radicals show that most of the pentanol radical isomers tend to isomerize to alkoxy radicals via a six-membered-ring or five-membered-ring transition state at low temperatures, producing ketones or aldehydes. At higher temperatures, the β-scission reactions are the main reaction channels for the consumption of pentanol radicals. A weak pressure dependence has been found for all isomerization reactions, and it becomes more and more important as pressure increases. The pressure dependence trends are different for the β-scission reactions of different branched pentanol radicals. In part I, the results for branched pentanol radical isomers are presented in detail, while in part II the results for linear pentanol radical isomers will be discussed.