Reactions of 1-hydroxy-1-methylethyl radicals with NO2-: Time-resolved electron spin resonance

摘要

The reaction of the alpha-hydroxyalkyl radical of 2-propanol (1-hydroxy-1-methylethyl radical) with nitrite ions was characterized. A product of the reaction was assigned as the adduct nitro radical anion, [HO-C(CH3)(2)NO2](center dot-). This radical was identified using time-resolved electron spin resonance (TRESR). The radical's magnetic parameters, the nitrogen hyperfine coupling constant (a(N) = 26.39 G), and its g-factor (2.0052) were the same as those of the nitro radical anion previously discovered in (OH)-O-center dot spin-trapping experiments with the aci-anion of (CH3)(2)CHNO2. Production of [HO-C(CH3)(2)NO2](center dot-) was determined to be 38% +/- 4% of the reaction of (CH3)(2)C-center dot-OH with nitrite. The reason why this fraction was less than 100% was rationalized by invoking the competitive addition at oxygen, which forms [HO-C(CH3)(2)ONO](center dot-), followed by a rapid loss of (NO)-N-center dot. Furthermore, by taking this mechanism into account, the bimolecular rate constant for the total reaction of (CH3)(2)C-center dot-OH with nitrite at reaction pH 7 was determined to be 1.6 x 10(6) M-1 s(-1), using both decay traces of (CH3)(2)C-center dot-OH and growth traces of [HO-C(CH3)(2)NO2](center dot-). This correspondence further confirms the nature of the reaction. The reaction mechanism is discussed with guidance by computations using density functional theory.