The slides contains the structural features, formation methods, stability and application of carbanion produces in organic reaction.

1. ORGANIC
INTERMEDIATES
CARBANIONS
Presented by : Akshay kank (M Pharm First Year)
Guided by : Dr. S.S. Pekamwar Sir
SWAMI RAMANAND TEERTH MARATHWADA UNIVERSITY (
PHARMACEUTICAL SCIENCES), NANDED.

2. CONTENTS
• INTRODUCTION
• STRUCTURE OF CARBANIONS
• FEATURES OF CARBANIONS
• FORMATION METHOD
• STABILITY OF CARBANIONS
• SYNTHETIC APPLICATION
• REFERENCES

3. INTRODUCTION
• AN ANION IN WHICH CARBON HAS AN UNSHARED PAIR OF ELECTRONS AND
CONTAINS A NEGATIVE CHARGE.
• A CARBANIONS IS ONE OF THE REACTIVE INTERMEDIATES IN ORGANIC
CHEMISTRY.
• THE CONJUGATE BASES OF WEAK ACIDS, STRONG BASES, EXCELLENT
NUCLEOPHILES.

4. INTRODUCTION
• THE NEGATIVE CHARGE GIVES GOOD NUCLEOPHILE PROPERTIES AND IT CAN
BE USED IN THE FORMATION OF NEW CARBON CARBON BOND.
• BOND CLEAVAGE: HETEROLYTIC CLEAVAGE

5. STRUCTURAL FEATURES OF CARBANIONS
• PYRAMIDAL- SP³ HYBRIDISED.
• BOND ANGLE 109.28
• GEOMETRY IS THUS TETRAHEDRAL.
• HAS EIGHT ELECTRONS.
• STABILIZED BY RESONANCE OR BY INDUCTIVE EFFECT.
• ACT AS BASE OR NUCLEOPHILE.

6. STRUCTURAL FEATURES
• CARBANIONS UNDERGOES RAPID INTERCONVERSION BETWEEN TWO
PYRAMIDAL FORMS.
• THE ENERGY BARRIER IS DIFFERENT FOR DIFFERENT TYPES OF
CARBANIONS.
• THE HIGHER ENERGY BARRIER OF TRIFLUOROMETHYL CARBANIONS IS DUE
TO THE MORE ELECTRONEGATIVITY OF FLUORINE ATOM WHICH IS MORE
STABILIZING THAN A HYDROGEN ATOM.

7. FORMATION OF CARBANIONS
• BY USING FOLLOWING WAYS:
1. PROTON ABSTRACTION
2. DECARBOXYLATION
3. ADDITION OF NUCLEOPHILE TO ALKENE
4. FORMATION OF ORGANOMETALLIC COMPOUND

8. FORMATION- PROTON ABSTRACTION
• WHEN PROTON IS ABSTRACTED FROM A CARBON CENTRE THEN THE
RESULTING ANION IS CALLED AS CARBANIONS
• THE ACIDIC HYDROGEN OF AN ORGANIC SUBSTRATE CAN BE ABSTRACTED
BY AN APPROPRIATE BASE FOR EXAMPLE CARBANIONS GENERATED FROM
CARBONYL COMPOUND.

9. FORMATION – DECARBOXYLATION
• DECARBOXYLATION OF CARBOXYLATE LEADS TO FORMATION OF
CARBANIONS INTERMEDIATE.

10. FORMATION – ADDITION OF NUCLEOPHILE
TO ALKENE
• CARBANIONS ARE GENERATED BY THE ATTACK OF NUCLEOPHILES ON ONE
OF THE CARBON OF AN ALKENE.

11. FORMATION – FORMATION OF
ORGANOMETALLIC COMPOUND
• METALS WHICH ARE LESS ELCTRONEGATIVE THAN CARBON(SUCH AS
MAGNESIUM, LITHIUM, POTASSIUM, SODIUM, ZINC, MERCURY, LEAD, THALLIUM
ETC.)
• THUS, METALLATION REVERSE THE POLARITY OF THE CARBON FROM
POSITIVE IN TO NEGATIVE IN ORGANOMETALLIC COMPOUND.
• REACTION OF ALKYL HALIDE WITH LITHIUM FORM ALKYL LITHIUM HAVING
NEGATIVE CHARGE ON CARBON.

12. STABILITY OF CARBANIONS
• FACTORS WHICH CAN STABILIZE OR DISPERSE THE NEGATIVE CHARGE ON
CARBON WILL STABILIZE A CARBANIONS
• STABILITY DEPENDS UPON FOLLOWING FACTORS:
1. INDUCTIVE EFFECT
2. EXTENT OF CONJUGATION OF THE ANION
3. HYBRIDIZATION OF THE CHARGE BEARING ATOM
4. AROMACITY

13. 1. INDUCTIVE EFFECT
• IF THE GROUPS ATTACHED TO CARBANIONS ARE ELECTRON RELEASING IN
NATURE THEY WILL INCREASES THE NEGATIVE CHARGE ON CARBON AND
THUS DISTABILIZE IT.
• HOWEVER ELECTRONEGATIVE ATOMS(F, CL, BR) OR ELECTRON
WITHDRAWING GROUPS (NO, CN, COOH, CO) ADJACENT TO THE NEGATIVELY
CHARGED CARBON WILL STABILIZE THE CARBANIONS.

14. 2. EXTENT OF CONJUGATION OF THE ANION
• 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.

15. 3. HYBRIDIZATION OF THE CHARGE
BEARING ATOM
• STABILITY OF ANION WILL DEPENDS UPON THE ‘S’ CHARACTER OF
CARBANIONS I.E MORE THE ‘S’ CHARACTER HIGHER WILL BE STABILITY OF
ANION.
• PERCENTAGE S CHARACTER IN THE HYBRID ORBITALS IS-
SP(50%) > SP²(33%) > SP³(25%)

16. 4. 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

17. SYNTHETIC APPLICATION OF CARBANIONS
• CARBOCATION ARE STRONG LEWIS ACIDS WHILE CARBANIONS ARE STRONG
BASES. SO THEY SHOWS MORE REACTIVITY TOWARDS EACH OTHER.
• CARBANIONS ARE PART OF MOST OF THE COMMON REACTION TYPES SUCH
AS-
1. DISPLACEMENT REACTION
2. ELIMINATION REACTION( E1 )
3. CONDENSATION
4. ADDITION REACTION
5. REARRAGEMENT REACTION
6. POLYMERIZATION ETC.

18. REFERENCES
• REACTIVE INTERMEDIATES IN ORGANIC CHEMISTRY STRUCTURE,
MECHANISM AND REACTIONS BY MAYA SHANKAR SINGH, WILEY-
VCH PUBLICATION.
• ORGANIC CHEMISTRY AN INTERMEDIATES, TEXTBOOK, SECOND
EDITION, BY ROBERT V. HOFFMAN, A JOHN WILEY AND SONS INC.
PUBLICATION.
• CARBANIONS AND FACTORS AFFECTING THEIR STABILITY,
HTTPS://WWW.SLIDESHARE.NET/MOBILE/KOSKAL/CARBANIONS -
39935663
• ORGANIC CHEMISTRY TUTORIALS: CARBANIONS
WWW.CHEM.UCLA.EDU/../CC.PDF
• ORGANIC CHEMISTRY BY ROBERT MORRISON AND ROBERT
BOYD, SEVENTH EDITION, PEARSON PUBLICATION

19. THANK
YOU