What is nucleophilic substitution reaction? What is SN1 and SN2 reaction?

In this blog post, you will learn about nucleophilic substitution reaction i.e SN1 and SN2 reactions.

If you want to learn about Elimination reaction-:E1 and E2 reaction mechanism

SN reaction is the reaction in which the weak nucleophile is substituted by strong nucleophile is called SN reaction.

The factors affecting the nucleophilic substitution reaction-:

  1. Nature of nucleophile
  2. Nature of solvent
  3. Nature of substrate

# Explain SN2 reaction mechanism with respect to hydrolysis of alkyl halide. OR explain the reaction mechanism for the reaction of primary alkyl halides with the alcoholic NaOH.

In SN2 reaction, the rate is directly proportional to the substrate and nucleophile


Rate α [substrate][nucleophile]

Generally hydrolysis of 1° alkyl halides follow SN2 reaction mechanism.

Mechanism of SN2 reaction-:

At first the nucleophile attacks the substrate carbon atom from oppostit side. Then since this is a SN2 reaction so a transition state will be formed which is pentavalent and very unstable. Here C-Br bond breaks easily and C-OH bond is formed. The product thus formed has inversion configuration because energy requird to break the C-Br bond is supplied by the energy required to form the C-OH bond.


Write the mechanism of the reaction of tertiary alkyl halides with

  1. Aqueous NaOH

  2. Alcoholic KOH


Explain the reaction mechanism of dehydrohalogenation of tertiary butyl bromide. What solvent favors the reaction mechanism?

The reaction where tertiary alkyl halides reacts with aq.NaOH is called SN1 reaction.

In SN1 reaction;

Rate α [substrate]

Mechanism of SN1 reaction-:

Step 1-: the tertiary alkyl halid slowly ionizes to give tertiary carbocation. Here direct attack of nucleophile is not possible because bulky CH3 group doesn’t let to do direct attack.

Thus formed tertiary carbocation is trigonal planar and the bond angle is 120°.

Step 2-: thus formed carbocation is very much unstable and reactive. So the nucleophile attacks from back is called inversion product and the product formed when nucleophile attacks from the front is called retention product.

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