Satpathy Lopamudra, Sahu Prabhat K, Behera Pradipta K, Mishra Bijay K
Centre of Studies in Surface Science and Technology, School of Chemistry , Sambalpur University , Jyoti Vihar 768 019 , India.
Computational Modeling Research Laboratory , School of Chemistry Sambalpur University , Jyoti Vihar 768 019 , India.
J Phys Chem A. 2018 Jul 12;122(27):5861-5869. doi: 10.1021/acs.jpca.8b02687. Epub 2018 Jul 2.
Although substantial work has been undertaken on reaction pathways involved in base-promoted elimination reactions and bimolecular nucleophilic substitution reaction of F on CHCHX (X = Cl, Br, I), the effect of solvents with varying dielectric constants on the stereochemistry of each of the reaction species involved across the reaction profile have not yet been clearly understood. The present investigation reports the effect of solvents on the potential energy surfaces (PES) and structures of the species appearing in the reaction pathway of F with bromoethane. The PESs in the gas phase have been computed at MP2 level and CCSD(T) level. The performance of several hybrid density functional, such as B3LYP, M06, M06L, BHandH, X3LYP, M05, M05-2X, and M06-2X have also been investigated toward describing the elimination and nucleophilic substitution reactions. With respect to MAE values and to make the computation cost-effective, we have explored the implicit continuum solvent model, CPCM in solvents like cyclohexane, methanol, acetonitrile, dimethyl sulfoxide and water. The reactant complexes proceed through the subsequent steps to produce fluoroethane as the substitution product and ethylene as one of the elimination products. For elimination reaction both syn and anti elimination have been explored. The calculated relatives energies values, which are negative in the gas phase, are found to be positive in polar solvents since the point charge in the separated reactants are more stabilized than the dispersed charge in the transient complex, which has also been analyzed through NBO analysis.
尽管已经对涉及碱促进消除反应以及氟对CHCHX（X = Cl、Br、I）的双分子亲核取代反应的反应途径进行了大量研究，但具有不同介电常数的溶剂对整个反应过程中涉及的每个反应物种的立体化学的影响尚未得到清晰的理解。本研究报告了溶剂对氟与溴乙烷反应途径中出现的物种的势能面（PES）和结构的影响。气相中的PES已在MP2水平和CCSD(T)水平上进行了计算。还研究了几种杂化密度泛函，如B3LYP、M06、M06L、BHandH、X3LYP、M05、M05-2X和M06-2X在描述消除反应和亲核取代反应方面的性能。关于平均绝对误差（MAE）值并为了使计算具有成本效益，我们在环己烷、甲醇、乙腈、二甲基亚砜和水等溶剂中探索了隐式连续介质溶剂模型CPCM。反应物络合物经过后续步骤生成氟乙烷作为取代产物，乙烯作为消除产物之一。对于消除反应，已经研究了顺式消除和反式消除。计算得到的相对能量值在气相中为负，而在极性溶剂中为正，因为分离反应物中的点电荷比过渡络合物中的分散电荷更稳定，这也通过自然键轨道（NBO）分析进行了分析。
