β-环糊精中环氧苯乙烷与氢溴酸反应机理的理论研究/THE ORETICAL STUDY ON THE HBr-INDUCED

2018-11-24 14:23:00

环氧 CD oxide styrene 乙烷



本文主要采用了量子化学计算的方法对β-环糊精中环氧苯乙烷与氢溴酸的反应机理进行了理论研究,主要分为以下两个步骤来进行。
首先采用分子动力学模拟和量子化学计算方法对β-CD-环氧苯乙烷和β-CD-质子化的环氧苯乙烷形成的超分子体系进行了理论研究。结果表明质子化的环氧苯乙烷的苯基朝向β-CD的小口时体系最稳定,此时主客体的相互吸引作用相对较大;而对于非质子化的环氧苯乙烷,虽然其苯基朝向β-CD的大口较稳定,但由于主客体之间具有较大的排斥能,且此时主客体偶极矩方向是反向的,最终得到的包结物仍可能以苯基朝向β-CD的小口为主,电荷密度拓扑分析发现,当苯基取向β-CD的小口方向时,质子化以及非质子化的环氧苯乙烷都能与位于β-CD大口边沿的羟基形成氢键。因此,环氧苯乙烷在β-CD内相中的定位作用主要得益于诸如氢键以及偶极等较强的分子间相互作用。
在以上计算的基础上,采用了量子化学计算的方法对β-环糊精中环氧苯乙烷与氢溴酸的反应机理研究,并且与没有环糊精存在的条件下的反应机理进行了对比。发现环氧苯乙烷同氢溴酸的在环糊精中和没有环糊精存在的条件下的反应有可能是一个无势垒的质子和卤离子的同时作用的的过程。反应既不是SN2反应也不是SN1反应,反应过程中没有过渡态,并且,β-环糊精存在的条件下,反应之所以得到单一2-溴-1-苯基乙醇是由于β-环糊精的偶极作用;而在自由状态下之所以生成了单一的2-溴-2-苯基乙醇,是由于环氧苯乙烷自身的偶极作用。



The primary quantum study on the HBr-induced ring opening of styrene oxide in the presence of β-CD is carried out,and the reaction process could be divivided into two following parts.
On the one hand, The molecular dynamic simulation and quantum chemistry methods were employed to study the supramolecular systems of β-CD-styrene oxide and β-CD-protonated styrene oxide. The results show that, when the phenyl group of protonated styrene oxide points to the secondary rim of β-CD, the system is inclined to be more stable and its attractive energy is relatively larger. But the case for styrene oxide is disagreement with the protonated partner. However, in the view of kinetics, the phenyl group of styrene oxide maybe finally point to the secondary rim of β-CD due to its comparatively less repulsive energy in the complex. The property of electron density analyzed by topological study indicates that hydrogen bond has formed between the host and guest molecules when the phenyl group of guest molecules points to the secondary rim of β-CD. As a result, it is suggested that the orientation effect on styrene oxide in the inner phase of β-CD might mostly be attributed to the interactions between the host and guest molecules, such as H-bond, dipole action, etc.
On the baisis of the above,the reaction mechamism concering HBr-induced ring opening of styrene oxide in the presence of β-CD is investigated by quantum chemistry,compared to the reaction without β-CD. It is possible that bromine anion and proton react sinutaniously either inner of β-CD or in the free condition,and the reaction without transition is neither SN2 nor SN1,meanwhile due to the primary β-CD dipole influence the reaction without β-CD yield the only 2-bromine-2-phenylethanol in the presence ofβ-CD; Another reaction product is only 2-bromine-1-phenylethanol owing to styrene oxide intrinsic pole action in the free condition.