Yeary Paul E, Richard John P
Science & Mathematics Division, Alice Lloyd College, Pippa Passes, KY 41844.
Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000.
J Phys Org Chem. 2024 Jul;37(7). doi: 10.1002/poc.4600. Epub 2024 Feb 20.
Rate and product data are reported for the solvolysis reactions of twenty-seven mono, di (3,4) and tri (3,4,5) ring-substituted benzyl chlorides. The first order rate constant for solvolysis in 20% acetonitrile in water decrease from = 2.2 s for 4-methoxybenzyl chloride to 1.1 x 10 s for 3,4-dinitrobenzyl chloride. The product rate constant ratios / for solvolysis in 70/27/3 (v/v/v) HOH/TFE/MeOH range from a minimum of / = 8 to a maximum of 110. The rate data were fit to a four-parameter Hammett equation that separates the resonance and polar effects of the aromatic ring substituents on the reaction rate. Increases in the values of the Hammett reaction constants and are observed as the substituent constants or are increased. A sharp decrease in the product selectivity / = 26 for stepwise solvolysis of 4-methoxybenzyl chloride is observed as electron-withdrawing substituents are added to 4-methoxybenzyl ring due to a Hammond-effect on the position of the transition state for solvent addition to the substituted 4-methoxybenzyl carbocation reaction intermediates. Sharp increases in the selectivity / are observed with decreasing reactivity of other 3,4,5-subsituted benzyl chlorides due to anti-Hammond shifts on a two-dimensional More-O'Ferrall reaction coordinate diagram in the position of the transition state for a concerted solvolysis reaction.
报告了27种单环、二环（3,4位）和三环（3,4,5位）环取代苄基氯的溶剂解反应的速率和产物数据。在20%乙腈水溶液中溶剂解的一级速率常数从对甲氧基苄基氯的(k = 2.2 s^{-1})降低到3,4 - 二硝基苄基氯的(1.1×10^{-5} s^{-1})。在70/27/3（v/v/v）水/三氟乙醇/甲醇中溶剂解的产物速率常数比(k_{OH}/k_{TFE})范围从最小值(k_{OH}/k_{TFE}=8)到最大值110。速率数据拟合到一个四参数哈米特方程，该方程分离了芳环取代基对反应速率的共振(\sigma^{+})和极性(\sigma)效应。随着取代基常数(\sigma)或(\sigma^{+})增加，观察到哈米特反应常数(\rho)和(\rho^{+})值增加。由于对取代的对甲氧基苄基碳正离子反应中间体进行溶剂加成的过渡态位置存在哈蒙德效应，当吸电子取代基添加到对甲氧基苄基环上时，观察到对甲氧基苄基氯逐步溶剂解的产物选择性(k_{OH}/k_{TFE}=26)急剧下降。由于在协同溶剂解反应的过渡态位置的二维莫尔 - 奥费拉尔反应坐标图上存在反哈蒙德位移，随着其他3,4,5 - 取代苄基氯反应活性降低，观察到选择性(k_{OH}/k_{TFE})急剧增加。
