Theoretical studies on identity SN2 reactions of lithium halide and methyl halide: A microhydration model

Abstract

Reactions of lithium halide (LiX, X = F, Cl, Br and I) and methyl halide (CH₃X, X = F, Cl, Br and I) have been investigated at the B3LYP/6-31G(d) level of theory using the microhydration model. Beginning with hydrated lithium ion, four or two water molecules have been conveniently introduced to these aqueous-phase halogen-exchange S(N)2 reactions. These water molecules coordinated with the center metal lithium ion, and also interacted with entering and leaving halogen anion via hydrogen bond in complexes and transition state, which to some extent compensated hydration of halogen anion. At 298 K the reaction profiles all involve central barriers ΔE ( cent ) which are found to decrease in the order F > Cl > Br > I. The same trend is also found for the overall barriers (ΔE(ovr)) of the title reaction. In the S(N)2 reaction of sodium iodide and methyl iodide, the activation energy agrees well with the aqueous conductometric investigation.

Theoretical investigation on identical anionic halide‐exchange SN2 reaction processes on N‐haloammonium cation NH3X+ (X = F, Cl, Br, and I)

“…Theoretical investigation on gas-phase identical anion halideexchange reactions on N-haloammonium cation, a F-TEDA-BF 4 analogue, using CCSD(T) calculation, leads to the following conclusions:…”

“…In our former work, gas‐phase ion pair S N 2 reactions of lithium halide and methyl halide with inversion and retention mechanisms were reported,3 and further work of identity S N 2 reactions of lithium halide and methyl halide with a microhydration model has been done 4. Now we pay our attentions to identical halide exchange S N 2 reaction at heteroatom, it is well known on whose cation S N 2 reaction has been less studied.…”

“…The nucleophilic substitution reaction is a fundamental reaction that has played an important role in the development of modern physical organic chemistry 1, 2. Many endeavors have been paid to gas‐phase halide‐exchange S N 2 reactions at saturated carbon atom, and their gas‐phase energy profiles have been investigated theoretically and experimentally 3–17. However, the nature and generality of gas‐phase identical halide exchange S N 2 reactions remain poorly understood due to the difficulty in obtaining both appropriate pathway and reliable energy data experimentally.…”

“…[1,2] Many endeavors have been paid to gas-phase halide-exchange S N 2 reactions at saturated carbon atom, and their gas-phase energy profiles have been investigated theoretically and experimentally. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] However, the nature and generality of gas-phase identical halide exchange S N 2 reactions remain poorly understood due to the difficulty in obtaining both appropriate pathway and reliable energy data experimentally. Quantum chemistry happens to provide an alternative method to understand them.…”

Nucleophilic Aliphatic Substitution

“…114 The reactions all occur with inversion of configuration, and the rate decreases from X = I to X = F, in both series. The energies of the reaction complexes and transition state structure are given.…”