Introduction
Organic chemistry is the branch of chemistry that deals with the study of carbon compounds, their structure, properties, reactions, and preparation. Carbon has a unique ability to form a large number of compounds due to its tetravalency and catenation property.
Organic chemistry forms the backbone of pharmaceuticals, polymers, fuels, dyes, and biological molecules.
Tetravalency of Carbon
Carbon has four valence electrons.
Electronic configuration:
C = 1s2 2s2 2p2
Valency:
Valency = 4
Carbon forms four covalent bonds to complete octet.
Catenation
Catenation is the ability of carbon to form chains.
General structure:
C − C − C − C
This leads to formation of long chains, branched chains, and rings.
Types of Organic Compounds
1. Aliphatic Compounds
Open chain compounds.
Example:
CH3 − CH2 − CH3
2. Aromatic Compounds
Contain benzene ring.
General formula:
C6H6
3. Alicyclic Compounds
Cyclic but non-aromatic.
Classification of Organic Reactions
1. Substitution Reaction
Example:
CH4 + Cl2 → CH3Cl + HCl
2. Addition Reaction
Example:
C2H4 + H2 → C2H6
3. Elimination Reaction
Example:
C2H5OH → C2H4 + H2O
4. Rearrangement Reaction
Internal rearrangement of atoms.
Bond Formation in Organic Compounds
Sigma bond:
Head-on overlap
Pi bond:
Sidewise overlap
Hybridization
sp3 hybridization:
1s + 3p → 4 sp3
sp2 hybridization:
1s + 2p → 3 sp2
sp hybridization:
1s + 1p → 2 sp
Bond Parameters
Bond length:
Distance between nuclei
Bond angle:
Angle between bonds
Bond energy:
Energy required to break bond
Inductive Effect
Electron displacement along sigma bonds.
Order:
−I and +I effects
Resonance
Actual structure is hybrid of structures.
Representation:
Structure A ↔ Structure B
Hyperconjugation
Delocalization of electrons involving sigma bonds.
Electrophiles and Nucleophiles
Electrophile:
Electron deficient species
Example:
H+
Nucleophile:
Electron rich species
Example:
OH−
Types of Bonds Breaking
Homolytic cleavage:
A − B → A• + B•
Heterolytic cleavage:
A − B → A+ + B−
Reaction Intermediates
Carbocation:
C+
Carbanion:
C−
Free radical:
C•
Stability Order
Carbocation:
3° > 2° > 1° > CH3+
Carbanion:
CH3− > 1° > 2° > 3°
Isomerism
Compounds with same formula but different structure.
Structural Isomerism
Different connectivity
Stereoisomerism
Different spatial arrangement
Functional Groups
Define reactivity of organic compounds.
Examples:
−OH (alcohol)
−COOH (acid)
−CHO (aldehyde)
Purification Techniques
Crystallization
Used for solids
Distillation
Based on boiling point difference
Sublimation
Solid → gas directly
Chromatography
Separation based on adsorption
Qualitative Analysis
Detection of elements like N, S, halogens.
Quantitative Analysis
Determination of percentage composition.
Important Equations
Homolytic cleavage:
A − B → A• + B•
Heterolytic cleavage:
A − B → A+ + B−
Percentage composition:
% = (mass of element / molar mass) × 100
Common Mistakes
- Confusing nucleophile and electrophile
- Not understanding inductive effect
- Ignoring resonance structures
Exam Tips
- Practice reaction mechanisms
- Learn stability orders
- Focus on concepts, not memorization
Conclusion
Organic chemistry is essential for understanding chemical reactions and real-world applications. Mastery of basic principles helps in advanced studies.
FAQs
Q1. What is electrophile?
Electron deficient species
Q2. What is nucleophile?
Electron rich species
Q3. What is resonance?
Hybrid of multiple structures