Premium
Theoretical investigation on identical anionic halide‐exchange S N 2 reaction processes on N ‐haloammonium cation NH 3 X + (X = F, Cl, Br, and I)
Author(s) -
Xiong Yan,
Zhang Shuting,
Ling Xuege,
Zhang Xu,
Wang Jinyue
Publication year - 2011
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.23268
Subject(s) - chemistry , halogen , electronegativity , halide , nucleophile , polarizability , ion , solvent , crystallography , inorganic chemistry , molecule , catalysis , organic chemistry , alkyl
CCSD(T) calculations have been used for identically nucleophilic substitution reactions on N ‐haloammonium cation, X − + NH 3 X + (X = F, Cl, Br, and I), with comparison of classic anionic S N 2 reactions, X − + CH 3 X. The described S N 2 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 − + NH 3 X + , charge distributions, geometries, energy barriers, and their correlations have been investigated. Central barriers Δ E ≠ centfor X − + NH 3 X + 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 Δ E ≠ ovrrelative 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 Δ E comp 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 ( R 2 = 0.972) and proton affinity of halogen anions X − ( R 2 = 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 − + CH 3 X has disappeared. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011