Reaction mechanisms
Direct SN2 rebound survives bulky alkyl iodides
Open access · cc by · source: Europe PMC
Even with extra methyl groups on the alkyl iodide, Cl− and CN− still show a direct backward SN2 rebound channel at high collision energy rather than fully statistical dynamics.
How this study connects
Role on claims
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Evidence for the claim as stated.
Even with extra methyl groups on the alkyl iodide, Cl− and CN− still show a direct backward SN2 rebound channel at high collision energy rather than fully statistical dynamics.
Evidence for the claim as stated.
Study at a glance
- Design
- Other — Crossed-beam velocity-map imaging of Cl−/CN− with alkyl iodides plus computed SN2/E2 barriers
- N
- Collision energies 0.4, 1.1, and 1.9 eV across CH3I, CH3CH2I, and (CH3)2CHI
- Population
- Gas-phase ion–molecule SN2/E2 reactions
- Outcome
- Direct backward SN2 rebound persists even with steric methylation and outcompetes E2 above 1 eV
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Inspect source passages
Direct SN2 rebound survives bulky alkyl iodides
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
More than half of Cl− + CH3CH2I and CN− + CH3CH2I collisions at 1.9 eV follow direct rebound.
Remarkably, more than half of the reactive collisions follow the direct rebound mechanism for Cl – + CH 3 CH 2 I and CN – + CH 3 CH 2 I at 1.9 eV.
Internal excitation does not exceed 60% of the available energy.
A higher amount of energy is dissipated in form of internal excitation in the reactions Cl – + CH 3 CH 2 I and Cl – + (CH 3 ) 2 CHI, however this fraction does not exceed 60% in any case.
Key findings
Direct backward SN2 opens at higher energy as methylation increases, yet at 1.9 eV more than half of Cl−/CN− + CH3CH2I events are direct rebound; energy into product internals stays below 60%. Direct SN2 outcompetes E2 above 1 eV.
Methodology
The authors crossed mass-selected Cl− or CN− with CH3I, CH3CH2I or (CH3)2CHI beams and recorded I− product velocity-map images at relative collision energies of 0.4, 1.1 and 1.9 eV, comparing angular/energy partitioning with computed SN2 and E2 barriers.
Limitations
These are isolated gas-phase ion–molecule collisions, not condensed-phase SN2 rates or stereochemical inversion yields in solution.
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