Organic Chemistry

Organic Chemistry is the study of carbon compounds. Carbon is unique due to its tetravalency and its ability to undergo catenation (forming long chains or rings of carbon atoms).

1. Tetravalency and Catenation

Carbon has four valence electrons, allowing it to form four covalent bonds. This tetravalency leads to a vast array of structures. Catenation is the ability of carbon atoms to link together in chains or rings.

2. Aliphatic Hydrocarbons

• Alkanes (CnH2n+2): Saturated hydrocarbons. They undergo substitution reactions (e.g., chlorination). Petroleum is a mixture of alkanes separated by fractional distillation. Cracking breaks large molecules into smaller ones, while reforming converts straight-chain alkanes into branched or cyclic ones to improve the octane number.
• Alkenes (CnH2n): Unsaturated hydrocarbons with a C=C double bond. They exhibit structural and geometric (cis-trans) isomerism. They undergo addition reactions and polymerization (e.g., polythene).
• Alkynes (CnH2n-2): Contain a C≡C triple bond. Ethyne (Acetylene) is prepared by the action of water on Calcium Carbide (CaC2). Terminal alkynes react with ammoniacal silver nitrate to form a white precipitate.

3. Aromatic Hydrocarbons

Benzene (C6H6) is the simplest aromatic compound. It has a hexagonal ring structure with delocalized pi electrons, which provides stability and makes it undergo substitution rather than addition reactions.

4. Alkanols (Alcohols)

Classified as primary (1°), secondary (2°), and tertiary (3°) based on the carbon attached to the -OH group. Ethanol is produced via fermentation of sugars using yeast. Lucas Test is used to distinguish them: 3° alcohols react instantly (turbidity), 2° in 5-10 mins, and 1° not at room temperature.

5. Alkanals and Alkanones

Alkanals (Aldehydes) and Alkanones (Ketones) both contain the carbonyl group (C=O). Alkanals are distinguished from alkanones using Tollens' reagent (silver mirror) or Fehling's solution (red precipitate), which react with alkanals but not alkanones.

6. Alkanoic Acids and Alkanoates

Alkanoic acids (R-COOH) react with alkanols to form Alkanoates (Esters) in a process called esterification. Fats and oils are natural alkanoates. Saponification is the alkaline hydrolysis of fats to produce soap and glycerol.

7. Biomolecules

• Carbohydrates: Classified into Monosaccharides (glucose), Disaccharides (sucrose), and Polysaccharides (starch/cellulose). Dehydration with conc. H2SO4 chars them to black carbon.
• Proteins: Polymers of amino acids. Tests include: Biuret (violet/purple), Millon’s (red), and Xanthoproteic (yellow/orange).

8. Polymers

Addition Polymers: Formed from monomers with double bonds (e.g., PVC, Polythene). Condensation Polymers: Formed with the elimination of a small molecule like water (e.g., Nylon, Terylene). Thermoplastics soften on heating, while Thermosetting plastics do not.