Some Basic Principles of Organic Chemistry – JEE Mains Chemistry

• by Zenith LMS
• Updated April 2025

1. Tetravalency of Carbon

Carbon is tetravalent, meaning it can form four covalent bonds with other atoms. This property enables carbon to form a wide variety of compounds, including chains, rings, and networks. The tetravalency of carbon is fundamental to the structure of organic compounds.

2. Shapes of Simple Molecules - Hybridization

Hybridization is the process in which atomic orbitals combine to form new hybrid orbitals. For example:

• sp3 Hybridization: Seen in methane (CH₄), resulting in a tetrahedral geometry.
• sp2 Hybridization: Seen in ethene (C₂H₄), resulting in a trigonal planar geometry.
• sp Hybridization: Seen in ethyne (C₂H₂), resulting in a linear geometry.

3. Classification of Organic Compounds

Organic compounds can be classified based on the functional groups present and their atoms of attachment. These include:

• Halogens: Compounds containing halogen atoms like chlorine or bromine (e.g., alkyl halides).
• Oxygen: Alcohols, aldehydes, ketones, and acids are all oxygen-containing compounds.
• Nitrogen: Compounds containing nitrogen include amines, amides, and nitriles.
• Sulfur: Sulfur-containing compounds include thiols and sulfides.

4. Homologous Series

A homologous series is a group of organic compounds with the same functional group and similar chemical properties but differing by a constant unit (such as a CH₂ group). For example, alkanes, alkenes, and alkynes are all homologous series.

5. Isomerism

Isomerism occurs when two or more compounds have the same molecular formula but different structures or spatial arrangements. Types of isomerism include:

• Structural Isomerism: Occurs due to different connectivity of atoms (e.g., butane and isobutane).
• Stereoisomerism: Occurs due to different spatial arrangement of atoms (e.g., cis-trans isomerism in alkenes).

6. Nomenclature of Organic Compounds

Organic compounds can be named using two systems:

• Trivial Nomenclature: Common names like ethanol, acetic acid, etc.
• IUPAC Nomenclature: Systematic naming based on the structure of the compound, such as methanol (CH₃OH) or ethanoic acid (CH₃COOH).

7. Covalent Bond Fission

When a covalent bond breaks, the resulting fragments can carry either a positive or negative charge. This can occur in two ways:

• Homolytic Fission: Each fragment gets one electron, forming free radicals.
• Heterolytic Fission: One fragment takes both electrons, forming ions like carbocations or carbanions.

8. Stability of Carbocations, Carbanions, and Free Radicals

The stability of these intermediates is crucial for the understanding of organic reactions.

• Carbocations: Stable when alkyl groups or electron-donating groups are attached (e.g., tertiary carbocations are more stable than primary carbocations).
• Carbanions: Stable when electron-withdrawing groups are present (e.g., fluorine or nitro groups).
• Free Radicals: Stability increases with the number of alkyl groups attached to the radical center.

9. Electrophiles and Nucleophiles

Electrophiles are electron-deficient species that seek to accept electrons, while nucleophiles are electron-rich species that seek to donate electrons. Both play key roles in organic reactions.

10. Electronic Displacement in a Covalent Bond

The displacement of electrons in a covalent bond can be explained by various effects:

• Inductive Effect: The shifting of electron density through sigma bonds, usually due to electronegativity differences.
• Electromeric Effect: The shift of electrons in a double bond under the influence of an attacking reagent.
• Resonance: The delocalization of electrons across adjacent atoms, as seen in the benzene ring.
• Hyperconjugation: The delocalization of electrons from adjacent C-H or C-C bonds to an empty p-orbital or π-orbital.

11. Types of Organic Reactions

Organic reactions can be classified into several major types, including:

• Substitution Reactions: A functional group is replaced by another (e.g., halogenation of alkanes).
• Addition Reactions: Two reactants add together to form a new product (e.g., hydrogenation of alkenes).
• Elimination Reactions: A small molecule is eliminated from the reactant (e.g., dehydration of alcohols to form alkenes).
• Rearrangement Reactions: Atoms or groups within a molecule rearrange to form an isomer (e.g., Beckmann rearrangement).