This document summarizes a student's report on carbocation reaction intermediates. It introduces carbocations as positively charged carbon species that are generally unstable. The document then covers: - Classification of primary, secondary, and tertiary carbocations - Carbocation structure and generation mechanisms - Factors that influence carbocation stability such as inductive effects, hyperconjugation, and resonance - Common reactions of carbocations including combination with nucleophiles, elimination of protons, addition to unsaturated systems, and intramolecular rearrangements.

1. SAMRAT PRITHVIRAJ CHAUHAN,
GOVERNMENT COLLEGE,AJMER
DEPARTMENT OF CHEMISTRY
REACTION INTERMEDIATE- CARBOCATION
SUBMITTED BY- MAMTA SONI
M.SC.CHEMISTRY SEMESTER 1st
.

2. • CONTENT
• INTRODUCTION OF CARBOCATION
• CLASSIFICATION OF CARBOCATION
• STRUCTURE OF CARBOCATION
• GENERATION OF CARBOCATION
• STABILITY OF CARBOCATION
• REACTIONS OF CARBOCATION

3. • INTRODUCTION
• The species which are formed as intermediate during the
progress of reaction are called reaction intermediates.
• The important reaction intermediate which are formed in the
organic reaction are:
1. Carbocation
2. Carbanion
3. Carbene
4. Nitrene
5. Free radicals

4. • INTRODUCTION OF CARBOCATION
• A carbocation is an ion in which carbon atom is positively
charge .for example
• Carbocation are generally unstable because the do not have
eight electrons to satisfy the octet rule.Therefor carbocation
are electrophilic species and thus act as Lewis acid.

5. • Two terms carbenium and carbonium are often used.
• Carbenium ion is a carbocation of the trivalent type.
• Carboniam ion is a carbocation of penta coordinated non
classical type.
Carbenium ion Carboniam ion

6. • They are generally named by suffixing the word cation.
METHYL ETHYL ISOPROPYL TERT - BUTYL

7. • CLASSIFICATION
• Carbocation may be classified into primary ,secondary and
tertiary depending upon the nature of carbon atom bearing
positive charge.
• If no carbon is attached to positively charged carbon atom then it
is simply called METHYL CARBOCATION.

8. • A primary carbocation is one in which there is one carbon group
attached to the positively charged carbon atom.
• A secondary carbocation is one in which there is two carbon groups
attached to the positively charged carbon atom.
• A tertiary carbocation is one in which there is three carbon groups
attached to the positively charged carbon atom .
primary secondary tertiary

9. • STRUCTURE OF CARBOCATION
• The positively charged carbon of the carbocation is sp2 hybridized.
• This carbon used the three sp2 hybridized orbitals for single bonding to 3
substituents.
• The unhybridised p – orbital remain vacant.
• Due to sp2 hybridization carbocation possesses trigonal planer structure
with the bond angle of 120° between them.

10. • GENERATION OF CARBOCATION
• The carbocation can be found in many organic reaction
mechanism ,but most carbocation are formed by one of only
following two basic mechanism steps:
• Ionization of carbon-leaving group bond.
• Electrophilic addition to a pi bond.

11. 1. HETROLYTIC BOND CLEAVAGE
• Ionization of alkyl halide.
• Determination of amine by nitrous acid(HNO2).

12. 2.PROTONATON
1.Protonation of alkenes:

13. • Protonation of alcohols followed by dehydration:

14. • STABILITY OF CARBOCATION
• The stability of carbocations is dependent on a few factors. Any structural
features which disperse the positive charge of the carbon atom will
increase its stability .Some factors are given below:
• 1.BY INDUCTIVE EFFECT.
• 2.BY HYPERCONJUGATION.
• 3.BY RESONANCE
• 4.BY AROMATISATION

15. • The stability of alkyl carbocation can be explained by:
1.Inductive effect 2 Hyperconjugation
• Inductive effect
+I effect group ( electron releasing ) stabilises the Carbocation because the
increase the electron density on cationic carbon.
• Hyperconjugation
Increasing the number of alkyl substituents increase the stability of
carbocation.
This is due to orbital overlap between the sigma bond and the empty p-orbital
of the sp2 carbon.

16. • Resonance effect always dominant over inductive effect and
hyperconjugation.
• As a result benzylic and allylic carbocation ( where the positively charged
carbon is conjugated to one or more double bond) significantly more
stable.

17. • The stability of phenylmethyl carbocation Can be explained
by resonance.
• Phenyl carbocation are most stable then alkyl carbocation
due to the number of resonating structures.

18. • Stability of carbocation by Aromaticity:
• Cyclic conjugated carbocation obeying huckle rule (4n+2) are
stable because they are aromatic and there is complete
delocalization of positive charge.
• Tropylium carbocation is more stable then
then triphynylmethyl carbocation.

19. • Exceptional stability: Cyclopropyl methyl carbocation
• These carbocation are very stable carbocation .They are
more stable then benzyl carbocation.
• The special stability is a result of conjugation between the
bent orbital of the cyclopropyl ring and vacent p – orbital of
cation carbon.

20. • ORDER OF STABILITY OF DIFFERENT CARBOCATION:

21. REACTIONS OF CARBOCATIONS
• Carbocation may undergo four basic type of reactions:
1. Combination with nucleophile.
2. Elimination of proton.
3. Addition to unsaturated system.
4. Intramolecular rearrangements
1. Combination with a nucleophile

22. • 2.Elimination of proton
• Carrbocation may loose form the adjacent atom.
• 3.Addition to unsaturated linkage

23. 4.Intramolecular rearrangements
• Shift of hydrogen atom:
• Shift of alkyl group:

24. •REFERENCES:
•Advanced organic chemistry ,by
Dr.Jagdamba Singh & Dr. L.D.S. Yadav.