COMPLETE KINETIC ISOTOPE EFFECT DESCRIPTION OF TRANSITION-STATES FOR ACID-CATALYZED HYDROLYZES OF METHYL ALPHA-GLUCOPYRANOSIDES AND BETA-GLUCOPYRANOSIDES
COMPLETE KINETIC ISOTOPE EFFECT DESCRIPTION OF TRANSITION-STATES FOR ACID-CATALYZED HYDROLYZES OF METHYL ALPHA-GLUCOPYRANOSIDES AND BETA-GLUCOPYRANOSIDES
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DOI：
10.1021/ja00283a025
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发表时间：
1986-11-12
影响因子：
15
通讯作者：
SINNOTT, ML
中科院分区：
文献类型：
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作者：
BENNET, AJ;SINNOTT, ML
以下动力学同位素效应（klight/kheavy）已经通过同位素准外消旋方法对甲基α-羟甲基纤维素的水解进行了测量。和β-葡萄糖苷，分别溶于2.0M HClO 4中，80 ℃。C（α- D 1.137 .+-。0.007，1.089。0.006; β- D 1.073 .+-. 0.003，1.045。0.004; γ- D（C5）0.987 ±. 0.002，0.971。0.003;离去基团d3 1.006。0.001，1.015。0.002;离开基团18 O 1.026。+-。0.001，1.024。0.001;环18 O 0.9965。+-。0.001，0.991。0.002;异头13 C 1.007 ±. 0.001，1.011。0.002）。结合添加的溶质对各种吡喃醛糖基衍生物的水解速率的影响的研究，其表明这样的反应是真正单分子的，并且模型环18 O和β-吡喃醛糖基衍生物的水解速率是180和β-吡喃醛糖基衍生物的水解速率。氘效应，有可能定位二面角周围的O 5-C1和C1-C2键在过渡态使用这些数据。如果这样导出的二面角在使用N.L. Allinger的MM 2分子力学程序，得到了过渡态结构。这些过渡态的几何形状与“立体电子控制理论”相矛盾。
The following kinetic isotope effects (klight/kheavy) have been measured by the isotopic quasi-racemate method for the hydrolyses of methyl .alpha.- and .beta.-glucopyranosides, respectively in 2.0 M HClO4 at 80.degree. C (.alpha.-D 1.137 .+-. 0.007, 1.089 .+-. 0.006; .beta.-D 1.073 .+-. 0.003, 1.045 .+-. 0.004; .gamma.-D (C5) 0.987 .+-. 0.002, 0.971 .+-. 0.003; leaving group d3 1.006 .+-. 0.001, 1.015 .+-. 0.002; leaving group 18O 1.026 .+-. 0.001, 1.024 .+-. 0.001; ring 18O 0.9965 .+-. 0.001, 0.991 .+-. 0.002; anomeric 13C 1.007 .+-. 0.001, 1.011 .+-. 0.002). In conjunction with studies of the effect of added solutes on the rates of hydrolysis of various aldopyranosyl derivatives, which indiate such reactions are truely unimolecular, and model ring 18O and .beta.-deuterium effects, it is possible to locate the dihedral angles about the O5-C1 and C1-C2 bonds at the transition state using these data. If the dihedral angles so derived are used as constraints in calculations using N.L. Allinger''s MM2 molecular mechanics program, transition-state structures are obtained. The geometry of these transition states stands in contradiction to the "theory of stereoelectronic control".