What are nucleophilic and electrophilic substitution reactions?

1 Answer
Jul 6, 2016

Here's my explanation.

Explanation:

A nucleophilic substitution is a reaction in which an electron pair donor (a nucleophile, "Y:") reacts with an electron pair acceptor (the substrate, "R-X") and substitutes for the "X" group (the leaving group).

A typical general equation is

underbrace("Y:"^"-")_color(red)("nucleophile") +underbrace("R"-"X")_color(red)("substrate") → "Y-R" + underbrace(":X"^"-")_color(red)("leaving group")

where "R" can be either an alkyl or an aryl group.

The mechanisms are different for aliphatic and aromatic nucleophilic substitutions, but the overall result is the same:

A nucleophile "Y" replaces a leaving group "X".

Specific examples are

":CN"^"-" + "CH"_3"Br" → "CH"_3"CN" + ":Br"^"-"

and

chemwiki.ucdavis.edu

An electrophilic substitution is a reaction in which an electrophile "E" substitutes for another atom or group "Y" in a compound "R-Y"

A typical general equation is

"E"^+ + "R-Y" → "E-R" + "Y"^+

where "R" can be either an alkyl or an aryl group.

An example is an electrophilic aromatic halogenation.

www.cliffsnotes.com

In the above reaction, a "Br" atom substitutes for a hydrogen atom.

Electrophilic aliphatic substitutions are relatively uncommon.

One important example is the replacement of the metal atom in an organometallic compound by hydrogen:

"R-M" + "H"^+ → "R-H" + "M"^+

The decomposition of a Grignard reagent by acid is an example.

"CH"_3"CH"_2"-MgBr" + "H"^+ → "CH"_3"CH"_2"-H" + ""^+"MgBr"