Kinetic isotope effects for hydrogen abstractions from n-alkanes by hydrogen atoms in the gas phase

Abstract

Kinetic isotope effects kH/kDfor the reactions H•+n-Cn H2n+2(n-Cn D2n+2) →kH(kD)H2(HD)+Cn H2n+1•(Cn D2n+1•) have been measured using hydrogen atoms produced in the radiolysis of water vapor. The normal alkanes investigated were n-hexane, n-heptane, n-octane, n-nonane, and n-decane. Regardless of the chain lengths of the n-alkanes studied, the results can be expressed within the experimental error with an Arrhenius type equation kH/kD =(0.47±0.03) exp [(9.41±0.21) kJ mol−1/RT] over the temperature range of 363–463 K. The experimental results were compared with theoretical calculations using transition-state theory and the London–Eyring–Polanyi–Sato (LEPS) potential-energy surface. Good agreement between experimental and calculated values was obtained when allowance was made for tunneling effects.