ALKOXY RADICAL ISOMERIZATION PRODUCTS FROM THE GAS-PHASE OH RADICAL-INITIATED REACTIONS OF 2,4-DIMETHYL-2-PENTANOL AND 3,5-DIMETHYL-3-HEXANOL

The products of the gas-phase reactions of the OH radical with 2,4-dimethyl-2-pentanol and 3,5-dimethyl-3-hexanol in the presence of NOx have been determined at atmospheric pressure of air and 296 +/- 2 K to assess the occurrence and importance of alkoxy radical isomerization. The products identified and quantified and their formation yields were as follows: from 2,4-dimethyl-2-pentanol: acetone, 0.92 +/- 0.15; 2-methylpropanal, 0.209 +/- 0.022; 4-methyl-2-pentanone, 0.046 +/- 0.008; and 4-hydroxy-4-methyl-2-pentanone, 0.116 +/- 0.018; from 3,5-dimethyl-3-hexanol: acetone, 0.120 +/- 0.029; 2-butanone, 0.275 +/- 0.021; 2-methylpropanal, 0.169 +/- 0.016; 4-methyl-2-pentanone, 0.161 +/- 0.012; and 4-hydroxy-4-methyl-2-pentanone, 0.250 +/- 0.023. The observed formation of 4-hydroxy-4-methyl-2-pentanone provides conclusive evidence for the occurrence of isomerization of the alkoxy radicals (CH3)(2)C(OH)CH2C(O)(CH3)(2) and CH3CH2C(CH3)(OH)CH2C(O)(CH3)(2) via 1,5-H shifts. The reaction mechanisms are discussed, and isomerization rate constants for 1,5-H-atom abstraction from the -CH3 and -CH2- groups in the RCH(2)C(CH3)(OH)-CH2C(O)(CH3)(2) alkoxy radicals (R = H and CH3) are derived.