The reactions of H/D with C2H6 and C3H8 have been studied with both shock-tube experiments and ab initio transition-state theory calculations. Rate constants for the reactions of D with C2H6 and C3H8 have been measured in reflected shock wave experiments over the temperature range, 1128–1299 K, at pressures 0.3–1 atm. D atoms are detected using atomic resonance absorption spectrometry. The measured D-atom profiles are sensitive to only the thermal dissociation of the D-atom source molecule, C2D5I, and to the title reactions. Since the dissociation has been previously studied in this laboratory, modeling the temporal evolution of the D-atom profiles allows determinations of the rate constants for the title reactions. Over the T range, 1128–1228 K, rate constants from the present experiments for D + C2H6 can be represented by the Arrhenius expression

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The experimental total rate constants for D + C3H8 over the T range, 1128–1299 K, can be represented by the Arrhenius expression

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The title reactions have been studied at the CCSD(T)/aug-cc-pv∞z level of theory using saddle point geometries at B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) levels of theory. The reaction endothermicities are in good agreement with current Active Thermochemical Tables values. Theoretical rate constants were estimated using transition state theory. The theoretical rate constants are in good agreement with the present experiments and lower temperature literature data. Over the T range of the present experiments, the theoretically predicted isotope effects are close to unity. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 194–205, 2012