Kandanarachchi Pramod H, Autrey Tom, Franz James A
Pacific Northwest National Laboratory, Fundamental Science Division, 902 Battelle Boulevard, Richland, Washington 99352, USA.
J Org Chem. 2002 Nov 15;67(23):7937-45. doi: 10.1021/jo025581k.
Arrhenius rate expressions were determined for beta-scission of phenoxyl radical from 1-phenyl-2-phenoxyethanol-1-yl, PhC*(OH)CH2OPh (V). Ketyl radical V was competitively trapped by thiophenol to yield PhCH(OH)CH2OPh in competition with beta-scission to yield phenoxyl radical and acetophenone. A basis rate expression for hydrogen atom abstraction by sec-phenethyl alcohol, PhC*(OH)CH3, from thiophenol, log(k(abs)/M(-1) s(-1)) = (8.88 +/- 0.24) - (6.07 +/- 0.34)/theta, theta = 2.303RT, was determined by competing hydrogen atom abstraction with radical self-termination. Self-termination rates for PhC*(OH)CH3 were calculated using the Smoluchowski equation employing experimental diffusion coefficients of the parent alcohol, PhCH(OH)CH3, as a model for the radical. The hydrogen abstraction basis reaction was employed to determine the activation barrier for the beta-scission of phenoxyl from 1-phenyl-2-phenoxyethanol-1-yl (V): log(k beta)/s(-1)) = (12.85 +/- 0.22) - (15.06 +/- 0.38)/theta, k beta (298 K) ca. (64.0 s(-1) in benzene), and log(k beta /s(-1)) = (12.50 +/- 0.18) - (14.46 +/- 0.30)/theta, k beta (298 K) = 78.7 s(-1) in benzene containing 0.8 M 2-propanol. B3LYP/cc-PVTZ electronic structure calculations predict that intramolecular hydrogen bonding between the alpha-OH and the -OPh leaving group of ketyl radical (V) stabilizes both ground- and transition-state structures. The computed activation barrier, 14.9 kcal/mol, is in good agreement with the experimental activation barrier.
确定了1-苯基-2-苯氧基乙醇-1-基（PhC*(OH)CH2OPh，V）的苯氧基自由基β-断裂的阿伦尼乌斯速率表达式。酮基自由基V与苯硫酚发生竞争捕获，生成PhCH(OH)CH2OPh，同时与β-断裂竞争生成苯氧基自由基和苯乙酮。通过仲苯乙醇（PhC*(OH)CH3）从苯硫酚中夺取氢原子的竞争反应与自由基自终止反应，确定了氢原子夺取反应的基准速率表达式：log(k(abs)/M(-1) s(-1)) = (8.88 ± 0.24) - (6.07 ± 0.34)/θ，θ = 2.303RT。使用Smoluchowski方程，以母体醇PhCH(OH)CH3的实验扩散系数作为自由基的模型，计算了PhC*(OH)CH3的自终止速率。利用氢夺取基准反应确定了1-苯基-2-苯氧基乙醇-1-基（V）的苯氧基β-断裂的活化能垒：log(k beta)/s(-1)) = (12.85 ± 0.22) - (15.06 ± 0.38)/θ，k beta (298 K)约为(64.0 s(-1)，在苯中)，以及log(k beta /s(-1)) = (12.50 ± 0.18) - (14.46 ± 0.30)/θ，k beta (298 K) = 78.7 s(-1)，在含有0.8 M 2-丙醇的苯中。B3LYP/cc-PVTZ电子结构计算预测，酮基自由基（V）的α-OH与-OPh离去基团之间的分子内氢键稳定了基态和过渡态结构。计算得到的活化能垒为14.9 kcal/mol，与实验活化能垒吻合良好。
