Absolute determinations of the kinetics and temperature dependences of the reactions of OH with a series of alkynes

Abstract

The rates of reaction of OH with propyne, but-1-yne, but-2-yne, pent-1-yne and hex-1-yne have been measured directly by using a discharge-flow resonance-fluorescence technique over a range of temperatures from 253 to 343 K. The room-temperature rate coefficients are compared with previous determinations; the new values for pent-1-yne and hex-1-yne fit into a general pattern of reactivity consistent with a mechanism involving initial electrophilic attack of OH at the triple bond. Similar trends are also presented for other series of reactions between radicals and unsaturated organic molecules. The temperature dependences of the rate constants for the OH + alkyne reactions are small or negative, suggesting that adduct formation is the initial step in the reaction mechanism.