Encyclopedia > Nucleophilic substitution

  Article Content

Nucleophilic substitution reaction

Redirected from Nucleophilic substitution

In chemistry, nucleophilic subsitution is a type of chemical reaction in which one nucleophile (electron donor) replaces another.

An example is the hydrolysis of halogenoalkanes by alkalis like hydroxide ions, OH-.

The two main mechanisms are called SN1 and SN2[?]. S stands for chemical substitution[?], N stands for nucleophilic, and the number represents the order of the reaction.


The SN1 reaction takes place in two steps.

  1. C(CH3)3Br --> C(CH3)3+ + Br-
  2. C(CH3)3+ + OH- --> C(CH3)3OH

This gives the overall reaction

C(CH3)3Br + OH- --> C(CH3)3OH + Br-

SN1 occurs where the central carbon atom is surrounded by bulky groups. The rate depends only on the concentration of the substrate.

rate = k[RX]

Because the intermediate cation, R+, is planar, an optically active[?] substrate gives a racemic mixture because nucleophilic attack[?] can occur from either side.


In the SN2 reaction, the addition of OH- and the elimination of Br- take place simultaneously.

SN2 occurs where the central carbon atom is easily accessible to the nucleophile. The rate is second order, depending on the nucleophile concentration as well as the substrate.

rate = k[RX][OH-]

The nucleophile enters on the opposite side of the carbon to the leaving group, so an optically active substrate has its structure inverted.

All Wikipedia text is available under the terms of the GNU Free Documentation License

  Search Encyclopedia

Search over one million articles, find something about almost anything!
  Featured Article
East Hampton North, New York

... There are 2,251 housing units at an average density of 155.8/km² (403.6/mi²). The racial makeup of the town is 82.46% White, 7.39% African American, 0.08% ...

This page was created in 38 ms