This document discusses carbanions, which are negatively charged carbon-containing species. It describes the structure of carbanions as sp3 hybridized and tetrahedral. Carbanions are stabilized by several factors, including inductive and resonance effects. The stability increases with increased s-character of the carbon atom and delocalization of the negative charge. Carbanions are nucleophilic and can be formed through deprotonation, decarboxylation, metal reduction, or addition to multiple bonds. They have applications in reactions like aldol condensation, Michael addition, Grignard reagents, and the Perkin reaction.

1. Presented by,
D.sujitha M.Pharm Ist sem
department of
pharmaceutical chemistry
CARBANION

2. CONTENT:
• Introduction
• Structure of carbanion
• Stability of carbanion
• Formation of carbanion
• Application
• Reference

3. INTRODUCTION
•Carbanion is a unit that contains a
negative charge on a carbon atom.
•Base/nucleophile depending upon the
reaction conditions.
•Negative charge gives good nucleophilic
properties to the unit that can be used
in the formation of new carbon–carbon
bonds.

4. CHARACTERISTIC OF CARBANION:
•Pyramidal,sp3 hybridised.
•Bond angle 109.28.
•Geometry-tetrahedral.
•It has 8 electrons.
•Act as good base or nucleophile.

5. Carbanion generally formed by heterolytic cleavage

6. • Carbanions undergoes rapid interconversion between 2
pyramidal forms.
• Tetrahedron can undergo inversion or retain its stereochemistry
depending upon the attached substituents.
• Methyl carbanion has a barrier to inversion of about 2 kcal mol–
1, whereas the trifluoromethyl carbanion has a barrier of 120
kcal mol–1.
• A fluorine atom is thus more stabilizing than a hydrogen atom
because of its high electronegativity

7. Stability of carbanion
• Inductive effect
• Resonance effect or delocalisation
• Aromaticity
• Electronegativity of carbanionic carbon
• Stabilisation by carbanion and enolate ion
• n
• Stabilisation by carbanion and enolate ion
Stability of carbanion

8. •Carbanion works as a nucleophile when attacks any
electron-deficient center except a proton.
•Stability and reactivity of a carbanion is determined by
several factors.
• The inductive effect: electronegative atoms adjacent to
the charge will stabilize the charge.

9. • Hybridization of the charge-bearing atom: the greater the s-
character of the charge-bearing atom the more stable the anion.
• Extent of conjugation of the anion: Resonance effects can
stabilize the anion.
• This is especially true when the anion is stabilized as a result of
aromaticity.

10. Inductive effect:
• Is an electronic effect due to polarisation of
bond within a molecule or ion.
• Electronegative atoms adjacent to the
charge will stabilize the charge
• Inductive effect decrease with distance
2 type: +I effect and –I effect.
• Shows electron donating group
+I effect
• Show Electron withdrawing
group- I effect

11. • Alkyl substitution at the carbanionic site results in an
intensification of the carbanionic character because of the
electron-donating character of the alkyl groups.
• Order of stability in carbanions is the reverse of that of
carbocations
• that is: vinyl > phenyl > cyclopropyl > primary > secondary >
tertiary

12. Resonance effect
• If negatively charged carbon is in
conjugation with a double bond the
resonance effects will stabilize the anion
by spreading out the charge by
rearranging the electron pairs.
• Number of resonating structure is
increase the stability of carbanion is
increase.
• Delocation of negative charge increase
the stability of carbanion

14. AROMATICITY
• In some carbanions the lone pair of electron of the negative
charge is involved in delocalization to add on to the aromatic
character of the molecule which gives them extra stability.
cyclopentadienyl anion

15. Electronegativity of carbanionic carbon
• Stability directly propotional to electronegativity of carbanionic carbon
which is directly propotional to % S- character of carbanionic carbon.
• The S-character is increase, then electronegativity also increase.
CH3
• sp3
CH2
• sp2
CH
• sp

16. Stabilisation by carbanion & enolate ion
• Stabilised by >C=o, -NO2, and CN groups present on
carbanionic carbon
• These groups stabilise carbanion by resonance effect.
• Stabilization of carbanion through formation of
enolate.
Contribution of structure (II) will be more than
(I)because in (II) negative charge is present on
electronegative oxygen

17. Formationof carbanion

18. Deprotonation from a C–H Bond:
• When proton is abstracted from a carbon center then the
resulting anion is called as carbanion.
• The acidic hydrogen of an organic substrate can be abstracted by
an appropriate base for example carbanions generated from
carbonyl compound.

19. DECARBOXYLATION
•Decarboxylation of carboxylate leads to formation of
carbanions intermediate.

20. Reduction of C–X Bond with Metal
• Metals which are less electro negative than carbon such as Mg, Na,
Hg, etc react with alkyl halide at appropriate condition to form the
carbon metallic bond
• where carbon contain negative charge and the metal contain
positive charge

21. A Negative Ion Adds to a Carbon–Carbon Double or
Triple Bond
• The addition of a negative ion to a carbon–carbon double or
triple bonds leads to a carbanion.
• The addition of a negative ion to a carbon–oxygen double bond
does not give a carbanion, since the negative charge resides on
the oxygen.
• Carbanions are also formed when a nucleophile adds to an α,β-
unsaturated compounds

22. APPLICATION
• Aldol condensation
• Cannizzaro reaction
• Dieckmann reaction
• Michael reaction
• Perkin reaction
• Clasein condensation
• Benzoin condensation

23. Aldol condensation.
• The reaction of an aldehyde or ketone with dilute base or acid to
form a beta- hydroxycarbonyl product.

25. Michael addition reaction:
• Reagents : commonly bases such as NaOH or KOH.
• The first step is the formation of the enolate.
• Enolates tend to react with α,β-unsaturated ketones via conjugate
addition.
• A conjugate addition with a carbanion nucleophile is known as
the Michael reaction or Michael addition.

27. Grignard reagents
• The strongest bases are obtained from the reaction of metal with
organohalogen compounds to give reagents known as Grignard
reagents
• Grignard reagents are examples of organo metallic carbanions.

29. Perkin reaction
• The condensation of aromatic aldehyde with anhydrides is
called as Perkin reaction. In this reaction formation of α,ß
unsaturated acid.

30. REFERENCE:
•Reactive intermediates in organic chemistry
structure, mechanism and reactions by Maya
Shankar Singh, wileyvch publication.Pg:no: 65-157.
•Advanced organic chemistry, reaction, mechanisms,
and structure by Jerry March. Pg: no: 175-185.