Unexpectedly Small Ortho-Oxygen Substituent Effects on Stabilities of Benzylic Carbocations
作者:M. Fujio、J. R. Keeffe、R. A. More O'Ferrall、A. C. O'Donoghue
DOI:10.1021/ja030446q
日期:2004.8.1
stimulated by the observation of small or inverse effects of replacement of an o-CH2 group by O or S in the cyclopentyl ring of indanol (kO/kCH2 = 1.2) or in the cyclohexyl ring of tetralol (kO/kCH2 = 0.6, kS/kCH2 = 0.3) on rates of carbocation formation. Values of pKR (KR = [ROH][H+]/[R+]) have been obtained by combining rate constants, kH, for the acid-catalyzed ionization of the alcohols with kH2O for attack
平衡常数被报道为苯甲醇电离成由环状或非环状邻烷基或邻氧取代基稳定的碳正离子。通过观察在茚满醇的环戊基环 (kO/kCH2 = 1.2) 或四氢萘酚的环己基环 (kO/kCH2 = 0.6) 中 O-CH2 基团被 O 或 S 取代的小的或相反的效应刺激了测量, kS/kCH2 = 0.3) 关于碳正离子形成的速率。pKR 的值 (KR = [ROH][H+]/[R+]) 是通过结合速率常数 kH 获得的,用于酸催化醇与 kH2O 电离以通过叠氮化物时钟测量水对碳正离子的侵蚀方法。对于衍生自以下醇的碳正离子,pKR 值如下所示:1-茚满醇,-11.7;2,3-二氢-3-羟基苯并呋喃(苯并呋喃水合物),-9.3;1-四氢萘酚,-12.2;4-色原醇,-12.0;4-硫色醇,-12.3;邻甲基-1-苯基乙醇,-13.8;o-甲氧基-1-苯基乙醇,-11.7。测量表明,与其小的动力学效应相反,在茚