In the following question I need to decide whether the reaction would undergo SN1 reaction or SN2 reaction.

enter image description here

I initially thought it would be SN1 since the resulting benzyl carbocation can be stabilized by resonance. Would the strongly electron withdrawing NO2 group destabilize it though? What kind of effect would this NO2 group have on the reactivity?


1 Answer 1


The reaction shown here is a Finkelstein reaction and SN2 reaction mechanism is followed.is an organic reaction that uses an alkyl halide exchange into another alkyl halide through a reaction wherein the metal halide salt is used. This reaction takes place at an equilibrium process by taking the advantage of poor acetone solubility in metal halide salt that is newly formed. The mechanism of the Finkelstein reaction is single-step SN2 reaction with stereochemistry inversion.

The success of this reaction depends on the below conditions.

  1. Nucleophilicity of your halogen
  2. Nature of leaving group
  3. Carbon-halogen bond
  4. Alkyl Halide reactivity

Holtz and Stock showed that electron-withdrawing groups increase the rate of SN2 reactions. This can be ascribed to stabilization of the transition state by withdrawal of some of the electron density. So NO2 will make reaction faster.


  • 1
    $\begingroup$ Can you give the reference for the Holtz and Stock work? $\endgroup$
    – Waylander
    Commented Apr 6, 2020 at 11:05
  • $\begingroup$ but isn't C-I bond weaker (i.e. less stable) than C-Cl bond? Would substitution really happen? I mean, if those 4 factors are what I need to consider, I don't see the driving force of the reaction. No reaction was also an option to pick for this question, would it be that? $\endgroup$
    – chemrese
    Commented Apr 6, 2020 at 12:27
  • 2
    $\begingroup$ @chemrese Believe the reaction is reversible however to my understanding it’s because iodide is a much better nucleophile than chloride and when it’s displaced, NaCl is insoluble in acetone whereas NaI is soluble. This essentially removes chloride from the system and so the equilibrium is forced to the right. $\endgroup$ Commented Apr 6, 2020 at 22:39

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