1.
CARBANIONS
Submitted by- PALLAVI VYAS
2020-2021
M.Sc chemistry semester 1st
S.P.C. GOVT. COLLEGE AJMER

2.
Content
1. Introduction of carbanion
2. Formation of carbanion
3. Factors affecting Stability of
carbanion
4. Reactions of carbanion

3.
Introduction of carbanion
 A carban carries three bonds and a lone pair of electron, thus making the
carbon atom negatively charged.
 Carbanion is represented as-
 Carbanion is the conjugate base of a carbon acid.

4.
 Carbanion has sp hybridization and trigonal pyramidal
geometry ( 3b.p. & 1l.p.). It has four sp hybrid orbitals.
 They have electron rich carbon atom having 8 electrons in its
valance shell.
 They are important chiefly as chemical intermediates
3
3

5.
Formation of carbanion
 The carbanions are obtained by heterolysis in which carban is
linked to less electronegative atom/group.
 The group attached to carban atom leaves behind the
bonding electron pair in cleavage; usually departing
constituent is a proton.
 Carbanion are also formed when nucleophile adds to
unsaturated compounds.

6.
Carbanions are formed from those compounds
which contain a functional group capable of
weakening a nearby C-H bond.

7.
Factors affecting stability
of carbanion
1. Inductive effect
-: The stability order of carbanion decreases, while
moving from primary to tertiary anion as alkyl group
has +I effect so due to this increase intensity of
negative charge on central carbon of tertiary anion.

8.
-: Less the pKa value more is the acidity & thus
more is the stability of acid anion.
pKa values of some alkanes :-

9.
2. Electronegativity
-: When the percentage of s-character
increase at the carbanionic carban then
stability also increase.

10.
3. Resonance effect.
-: Due to resonance,negative charge distribution occur so more
the distribution of negative charge more the stability of
carbonion.
# Relative stability of benzyl & allylic carbanion.

11.
#. Relative stability of benzylic carbanion and their substitution.

12.
2

13.
Reactions of carbanion
 Carbanions are very reactive & unstable.
 They undergo chemical reaction as soon as they are formed.
1. Addition reaction:- carbanions combine with another species that has empty
orbital in it’s outermost shell.
2. Elimination reaction:-This reaction takes place via formation of carbanion as
reaction intermediate.

14.
3. Substitution reaction:- The most important reaction of this category is the
alkylation of enolate which is an important synthetic method.
4. Rearrangement reaction:- Rearrangement takes place by 1,2 shift of alkyl or aryl
group from carbon to carbon,nitrogen to carbon & sulphur to carbon.

15.
Thank you
REFERENCE
Pragati prakashan
www.google.com