Aromaticity in Organic Chemical Compounds - Powerpoint Presentation

Description:
This presentation delves into the concept of aromaticity in organic chemistry, explaining the unique stability and reactivity of aromatic compounds. It provides a comprehensive overview of:

Historical background and discovery of aromaticity

Huckel’s Rule and criteria for aromaticity

Examples of aromatic, anti-aromatic, and non-aromatic compounds

Molecular orbital theory and resonance in aromatic systems

Applications of aromatic compounds in pharmaceuticals, dyes, and materials science

Problem-solving approaches with illustrative examples

The slides are structured for clarity and engagement, making it an excellent resource for classroom learning, academic projects, and seminar discussions.

1. Some important points

2. 18 VE Rule

3. Generating Carbocations
i.Direct ionization
❖ Removal of a more electronegative leaving group
❖ For eg. Solvolysis reaction of alkyl halides
X= Halogen atom like, Cl, Br, I

4. Generating Carbocations
ii.Ionization after an initial reaction
❖ An appropriate functional group is converted to a leaving
group
❖For eg. Protonation of alcohol, conversion of primary amine
to diazonium salt

5. Generating Carbocations
iii.Addition of a positive species
❖ A proton or a positive species can add to one atom of a
C=C or C≡C bond
❖ Addition of proton to C=X bond, where X is O, S, N, etc.

6. Reactions of Carbocations
❖Carbocations are short lived and they react easily
i.Lewis acid-base reaction
❖ Lewis base will donate electron to carbocation
❖ Reaction is very fast

7. Reactions of Carbocations
ii. Loss of a proton
❖ Carbocations may lose a proton from the adjacent carbon
❖ Presence of α hydrogens are required

8. Reactions of Carbocations
iii. Rearrangement reactions
❖ Intramolecular migration of an alkyl/aryl/hydrogen
❖ New positive charge generated at another carbon atom
❖ Rearrangement is driven by carbocation stability
1,2-Hydride shift Methyl shift

9. Reactions of Carbocations
iv. Addition to a double bond
❖ Carbocation may add to a double bond
❖ New positive charge generated at another carbon atom
❖ New carbocation formed can add to another alkene

10. Formation of Carbanions
-H
+
or
Heterolytic
cleavage
(i) Heterolytic Cleavage
❖A group attached to carbon leaves
❖Carbon retains both share of electrons
❖Leads to the formation of a carbanion

11. Formation of Carbanions
Proton abstraction
❖Leaving group is often a proton (H
+
)
❖Simple acid base reaction
❖Carbanion + conjugate acid is formed
Hydroxide
ion
Acetaldehyde Conjugate
acid
Carbanion

12. Formation of Carbanions
(ii) Addition of negative ion
❖Negatively charged ion like alkoxide ion
❖Addition occurs across a C=C or C≡C bond

13. Reaction of Carbanions
(i) Displacement Reaction
❖Carbanion attacks an electropositive centre
❖Attacks carbon atom having four bonds
❖One group is displaced by incoming carbanion

14. Reaction of Carbanions
(ii) Grignard Reaction
❖ Grignard reagent is an organomagnesium compound (RMgX)
❖ Carbanion of Grignard reagent attacks a carbonyl carbon
❖ Product is a secondary or tertiary alcohol

15. Reaction of Carbanions
(iii) Elimination Reaction
❖ Carbanion intermediates are formed in E1cb reaction
❖ Alpha carbon contains a leaving group
❖ Formation of an alkene

16. Reaction of Carbanions
(iv) Combination with a cation
❖ Carbanion generated from nucleophile addition to alkene
❖ Negative charge stabilized by combination with a cation
❖ Cation can be a proton or any positive ion

17. Aromaticity-modified Slides