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sn1

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AKASH GOYAL AskiitiansExpert-IITD
420 Points
13 years ago

Dear Akash

The SN1 reaction is a substitution reaction in organic chemistry. "SN" stands for nucleophilic substitution and the "1" represents the fact that the rate-determining step is unimolecular.  The reaction involves a carbocation intermediate and is commonly seen in reactions of secondary or tertiary alkyl halides under strongly basic conditions or, under strongly acidic conditions, with secondary or tertiary alcohols. With primary alkyl halides, the alternative SN2 reaction occurs.

An example of a reaction taking place with an SN1 reaction mechanism is the hydrolysis of tert-butyl bromide with water forming tert-butyl alcohol:

reaction tert-butylbromide water overall

This SN1 reaction takes place in three steps:

  • Formation of a tert-butyl carbocation by separation of a leaving group (a bromide anion) from the carbon atom: this step is slow and reversible.
SN1 mechanism: dissociation to carbocation
  • Nucleophilic attack: the carbocation reacts with the nucleophile. If the nucleophile is a neutral molecule (i.e. a solvent) a third step is required to complete the reaction. When the solvent is water, the intermediate is an oxonium ion. This reaction step is fast.
Recombination of carbocation with nucleophile
  • Deprotonation: Removal of a proton on the protonated nucleophile by water acting as a base forming the alcohol and a hydronium ion. This reaction step is fast.

Proton transfer forming the alcohol

 

All the best.

AKASH GOYAL

AskiitiansExpert-IITD

 

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