Kinetics of Reactions of CCN Radical with Alcohols

The reaction kinetics of cyanomethylidyne radical, CCN(X²), with a series of primary alcohols were studied at about 1.33 kPa total pressure and room temperature using pulsed laser photolysis/laser-induced fluorescence (LP/LIF) technique. The CCN radical was produced via laser photolysis of CCl₃CN with the fourth harmonic output of a Nd: YAG laser (266 nm). The relative concentration of the CCN(X²) radical was monitored by LIF in the (0, 0) band of the CCN(A² X²) transition at 470.9 nm. Under pseudo-first-order conditions, the reaction rate constants of CCN(X²) with a series of primary alcohol molecules (n-C_nH_2n+1OH, n=1-6) were determined by measuring the time evolution of the relative concentration of CCN(X²_i). The measured rate constants increased monotonously with the number of carbon atoms in the alcohols, and the values for reactions of CCN(X²) with alcohols were larger than those for reactions of CCN(X²) with alkanes (C₁-C₅). Based on the bond dissociation energies and linear free energy correlations, it was believed that the reactions of CCN(X²) with alcohols proceeded via a hydrogen abstraction mechanism that was analogous to CCN(X²) with alkanes. The experimental results indicated that the H atoms on the C-H bonds were activated at the presence of the OH group in alcohol molecules and the hydrogen abstraction from the C-H bonds in the alcohol molecules was the dominant reaction pathway. The relation between the rate constants and the long-distance attractive potentials between the CCN radical and the alcohol molecules was discussed.