No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Publisher's Note: “Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl” [J. Chem. Phys. 140, 054109 (2014)]
We have computationally studied the bimolecular nucleophilic substitution (SN 2) reactions of Mn NH2(n-1) + CH3 Cl (M+ = Li+ , Na+ , K+ , and MgCl+ ; n = 0, 1) in the gas phase and in tetrahydrofuran solution at OLYP/6-31++G(d,p) using polarizable continuum model implicit solvation. We wish to explore and understand the effect of the metal counterion M+ and of solvation on the reaction profile and the stereochemical preference, that is, backside (SN 2-b) versus frontside attack (SN 2-f). The results were compared to the corresponding ion-pair SN 2 reactions involving F- and OH- nucleophiles. Our analyses with an extended activation strain model of chemical reactivity uncover and explain various trends in SN 2 reactivity along the nucleophiles F- , OH- , and
NH
2
-
, including solvent and counterion effects. © 2019 Wiley Periodicals, Inc.
The nucleophilic attack of a chloride ion on methyl chloride is an important prototype SN2 reaction in organic chemistry that is known to be sensitive to the effects of the surrounding solvent. Herein, we develop a highly accurate Specific Reaction Parameter (SRP) model based on the Austin Model 1 Hamiltonian for chlorine to study the effects of solvation into an aqueous environment on the reaction mechanism. To accomplish this task, we apply high-level quantum mechanical calculations to study the reaction in the gas phase and combined quantum mechanical/molecular mechanical simulations with TIP3P and TIP4P-ew water models and the resulting free energy profiles are compared with those determined from simulations using other fast semi-empirical quantum models. Both gas phase and solution results with the SRP model agree very well with experiment and provide insight into the specific role of solvent on the reaction coordinate. Overall, the newly parameterized SRP Hamiltonian is able to reproduce both the gas phase and solution phase barriers, suggesting it is an accurate and robust model for simulations in the aqueous phase at greatly reduced computational cost relative to comparably accurate ab initio and density functional models.
The kinetics of the reaction system initiated by the Al13−+Cl2 reaction was experimentally studied in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The Al13− clusters were produced by laser desorption/ionization of LiAlH4, then transferred into the ICR cell, cooled by collisions with Ar, and exposed to an excess of Cl2 with a concentration of ∼ 108 cm−3. Relative concentration-time profiles of Aln− clusters with n = 13, 11, 9, and 7 as well as profiles of Cl− ions have been recorded. Other ionic species, besides traces of Al12Cl−, were not found, which indicates a double-step degradation mechanism via the odd-numbered Aln− clusters. From a kinetic analysis of the experimental results, a rate coefficient of (5±2)×10−10 cm3 s−1 for the Al13−+Cl2 reaction was obtained. Furthermore, it is inferred from a simultaneous fit of all concentration-time profiles that the Aln−+Cl2 reactions for n = 13, 11, 9, and 7 occur with rate coefficients near the Langevin limit in the range kbim ∼ (5±4)×10−10 cm3 s−1. The branching ratios between the Aln−2−-producing and Cl−-producing channels of a given cluster AlnCl2− indicate an increasing contribution of the Cl−-producing channels with decreasing cluster size. Statistical rate theory calculations on the basis of molecular data from quantum chemical calculations show that the experimental Aln− profiles are compatible with a sequence of association-elimination reactions proceeding via the formation of highly excited AlnCl2− adducts followed by a sequential elimination of two AlCl molecules. Rate coefficients for these reactions were calculated, and the production of Cl− was shown probably not to proceed via these AlnCl2− intermediates.