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Direct SN2 rebound survives bulky alkyl iodides
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.
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Which competing organic mechanisms were imaged for methylated alkyl iodides?
SN2 nucleophilic substitution versus E2 elimination.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
Does direct backward SN2 vanish once the alkyl iodide is methylated?
No—it still occurs at high collision energies for Cl− and CN− with methylated alkyl iodides.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
Above what energy is direct SN2 favoured over E2 and other SN2 paths?
Above 1 eV.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
What fraction of Cl−/CN− + CH3CH2I events at 1.9 eV are direct rebound?
More than half of the reactive collisions.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
How much energy goes into product internal modes for Cl− + ethyl/isopropyl iodide?
More than for CH3I, but never more than 60%.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
Do methylated substrates show direct rebound at 0.4 eV?
No; unlike CH3I, the methylated alkyl iodides show none at 0.4 eV.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
What fraction of Cl− + (CH3)2CHI at the same high E_rel is still direct rebound?
0.15—still significant given the bulky isopropyl iodide.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
What experimental method mapped product angles and speeds?
Crossed-beam velocity-map imaging of I− under single-collision conditions.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
Are anti-E2 barriers below the lowest experimental E_rel?
Yes—barriers are positive but lower than the lowest studied collision energy of 0.4 eV.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
What stereodynamic picture is proposed for the conserved rebound channel?
A collinear entrance-channel complex regardless of the alkyl iodide.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified
How many ion events typically make one velocity image?
30 000–40 000 events in the center-of-mass frame.
Source: Conservation of direct dynamics in sterically hindered S<sub>N</sub>2/E2 reactions · DOI · quote verified