Theoretical investigation on identical anionic halide‐exchange SN2 reaction processes on N‐haloammonium cation NH3X+ (X = F,Cl, Br,and I) |
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Authors: | Yan Xiong Shuting Zhang Xuege Ling Xu Zhang Jinyue Wang |
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Institution: | 1. College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030, China;2. Department of Chemistry and Chemical Engineering, Institute of Applied Chemistry, Key Laboratory of Computational Physics in Universities of Sichuan, Yibin University, Yibin 644007, China |
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Abstract: | CCSD(T) calculations have been used for identically nucleophilic substitution reactions on N‐haloammonium cation, X? + NH3X+ (X = F, Cl, Br, and I), with comparison of classic anionic SN2 reactions, X? + CH3X. The described SN2 reactions are characterized to a double curve potential, and separated charged reactants proceed to form transition state through a stronger complexation and a charge neutralization process. For title reactions X? + NH3X+, charge distributions, geometries, energy barriers, and their correlations have been investigated. Central barriers ΔE for X? + NH3X+ are found to be lower and lie within a relatively narrow range, decreasing in the following order: Cl (21.1 kJ/mol) > F (19.7 kJ/mol) > Br (10.9 kJ/mol) > I (9.1 kJ/mol). The overall barriers ΔE relative to the reactants are negative for all halogens: ?626.0 kJ/mol (F), ?494.1 kJ/mol (Cl), ?484.9 kJ/mol (Br), and ?458.5 kJ/mol (I). Stability energies of the ion–ion complexes ΔEcomp decrease in the order F (645.6 kJ/mol) > Cl (515.2 kJ/mol) > Br (495.8 kJ/mol) > I (467.6 kJ/mol), and are found to correlate well with halogen Mulliken electronegativities (R2 = 0.972) and proton affinity of halogen anions X? (R2 = 0.996). Based on polarizable continuum model, solvent effects have investigated, which indicates solvents, especially polar and protic solvents lower the complexation energy dramatically, due to dually solvated reactant ions, and even character of double well potential in reactions X? + CH3X has disappeared. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 |
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Keywords: | B3LYP CCSD(T) N‐haloammonium cation polarizable continuum model SN2 reactions |
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