Atomistic dynamics of elimination and nucleophilic substitution disentangled for the F− + CH3CH2Cl reaction

Abstract

Chemical reaction dynamics are studied to follow and understand the concerted motion of several atoms while they rearrange from reactants to products. With the number of atoms growing, the number of pathways, transition states, and product channels also increases and rapidly presents a challenge to experiment and theory. Here, we disentangle the competition between bimolecular nucleophilic substitution (S N 2) and base-induced elimination (E2) in the polyatomic reaction F - + CH 3 CH 2 Cl. We find quantitative agreement for the energy- and angle-differential reactive scattering cross sections between ion imaging experiments and quasi-classical trajectory simulations on a 21-dimensional potential energy hypersurface. The anti-E2 pathway is most important, but the S N 2 pathway becomes more relevant as the collision energy is increased. In both cases the reaction is dominated by direct dynamics. Our study presents atomic level dynamics of a major benchmark reaction in physical organic chemistry, thereby pushing the number of atoms for detailed reaction dynamics studies to a size that allows applications in many areas of complex chemical networks and environments.

Uncovering an oxide ion substitution for the OH− + CH3F reaction

“…As the masses of the product anions, considering the most abundant isotopes, F − (19 u), CH 2 F − (33 u), and CH 3 O − (31 u), are different, the experimental detection of the oxide ion substitution channel is possible. Note that a recent crossed-beam study could measure reaction channels with branching ratios less than 2%, 37 which further supports the future experimental observation of the low-probability oxide ion substitution. Furthermore, similar post-reaction proton-transfer processes revealed in the present work may occur in other chemical reactions as well, providing novel product channels.…”

Proton transfer-induced competing product channels of microsolvated Y−(H2O)n + CH3I (Y = F, Cl, Br, I) reactions

“…3,9,30 The competing product channels may share the same intermediates, such as the S N 2 and E2 product channels of F − + C 2 H 5 Cl that share the same pre-reaction complexes, but behave differently in their dynamics, as evidenced by their ion product velocity scattering distribution and product energy distribution. 19 The same phenomena were also observed between the S N 2 and PT reactions of HO − /F − + CH 3 I. 26,31…”

“…Recently, the combination of crossed-beam ion imaging experiments and dynamic simulations has improved our understanding of model S N 2 reactions in the gas phase. 12,[16][17][18][19][20][21][22] Various novel dynamical mechanisms that deviate from the double-well potential have been reported, including roundabout, 23 double inversion, 20 formation of hydrogen-bonded and halogen-bonded complexes, 24,25 and proton-exchange mechanisms. 26 The dynamics of the model Y À + CH 3 X/C 2 H 5 X reactions are complicated not only by their rich mechanisms 21 but also by their competing reactions.…”

Parameter free evaluation of SN2 reaction rates for halide substitution in halomethane

“…Despite their simplicity, they are continuously attracting the attention of theoretical/computational chemists. [2][3][4][5] It is a fundamental concept in organic chemistry that the electronegative halogen atom in alkyl halides creates a polar carbon-halogen bond. The electron-deficient carbon is thus susceptible to attack by nucleophiles.…”

“…Despite their simplicity, they are continuously attracting the attention of theoretical/computational chemists. 2–5…”