KINETIC ISOTOPE-EFFECT PROBES OF TRANSITION-STATE STRUCTURE - VIBRATIONAL ANALYSIS OF MODEL TRANSITION-STATES FOR CARBONYL ADDITION
KINETIC ISOTOPE-EFFECT PROBES OF TRANSITION-STATE STRUCTURE - VIBRATIONAL ANALYSIS OF MODEL TRANSITION-STATES FOR CARBONYL ADDITION
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DOI：
10.1021/ja00521a014
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发表时间：
1980-01-01
影响因子：
15
通讯作者：
SCHOWEN, RL
中科院分区：
文献类型：
--
作者：
HOGG, JL;RODGERS, J;SCHOWEN, RL
对H3*CC*H*O*与HO*-的羰基加成反应的1H/2H、12C/13C和16O/18O的动力学和平衡同位素效应进行了模型计算，包括两组密切相关的力场，以及在273-32.3℃范围内一系列可能的过渡态结构的亲核途径的曲线和垂直轨迹。在所有的计算中，几何特征和力常数被假定为从反应物的值向产物的值改变，与亲核-羰基键的Pauling键级B成比例。α-重氢效应和β-重氢效应是B的近线性函数，应该是过渡态结构的良好和一致的探针。羰基-18O效应是正常的，并且如预期的那样，随着B的增加而稳步增加。亲核-18O效应对伯氏杆菌来说是正常的。0.5，对于较晚的过渡态则相反。羰基-13C是.apprx。1.03用于早期过渡态，并下降到反平衡效应。没有计算出明显反常的温度依赖关系。羰基加成反应是化学和生物化学领域的研究热点，从过渡态结构的角度理解其动力学是当前研究的热点。
Model calculations of the 1H/2H, 12C/13C and 16O/18O kinetic and equilibrium isotope effects at the starred positions for the carbonyl addition reaction of H3*CC*H*O* with HO*- were made for 2 closely related sets of force fields, and for both curved and perpendicular trajectories of nucleophilic approach to carbonyl, for a series of possible transition-state structures at temperatures from 273-323.degree. K. In all calculations, the geometrical features and force constants were assumed to change from reactant values toward product values in proportion to the Pauling bond order B of the nucleophile-carbonyl bond. The .alpha.-deuterium and .beta.-deuterium effects are nearly linear functions of B and should be good and consistent probes of transition-state structure. The carbonyl-18O effect is normal and increases steadily with B, as expected. The nucleophile-18O effect is normal for B .ltorsim. 0.5 and inverse for later transition states. The carbonyl-13C is .apprx. 1.03 for early transition states and falls to an inverse equilibrium effect. No strikingly anomalous temperature-dependences were calculated. Carbonyl-addition reactions are of interest in chemistry and biochemistry and the understanding of their dynamics in terms of transition-state structure is the topic of much current research.