Introduction to Organic Chemistry
Organic Chemistry is the chemistry of hydrocarbons and their derivatives where carbon is covalently bonded. Originally thought to be from living organisms under vital force, but disproved by syntheses like urea by Wohler and acetic acid by Kolbe.
Berthelot prepared methane, cellulose is most abundant. Kekule proposed tetravalency, Van't Hoff tetrahedron model.
Purification of Organic Compounds
Purification depends on nature (solid/liquid) and impurities. Common methods include crystallization, distillation, sublimation, chromatography.
Drying and Purity Criteria
- Solids: Press, oven, desiccator
- Liquids: Anhydrous agents like CaCl₂
- Purity: Sharp m.p./b.p., mixed m.p. test
Qualitative Analysis (Detection of Elements)
Carbon and hydrogen via copper oxide test. Other elements via Lassaigne's test (sodium fusion).
| Element | Test | Observation |
|---|---|---|
| Nitrogen | FeSO₄ + NaOH + HCl + FeCl₃ | Prussian blue |
| Sulphur | Sodium nitroprusside | Purple |
| Halogens | AgNO₃ | White (Cl), pale yellow (Br), yellow (I) |
| N + S | FeCl₃ | Blood red |
Other Tests
Quantitative Analysis (Estimation of Elements)
Percentage composition determination for C, H, N, halogens, S, P, O.
Carbon and Hydrogen
Nitrogen
Other Elements
| Element | Method | Formula |
|---|---|---|
| Halogens | Carius | %X = (atomic mass X / mol mass AgX) × (AgX mass / compound mass) × 100 |
| Sulphur | Carius | %S = 32/233 × (BaSO₄ mass / compound mass) × 100 |
| Phosphorus | Carius | %P = 31/222 × (Mg₂P₂O₇ mass / compound mass) × 100 |
| Oxygen | Direct/Indirect | %O = 100 - (%C + %H + %N + ...) |
Empirical and Molecular Formula
Empirical: Simplest ratio from % composition. Molecular = n × Empirical, n = Mol mass / Emp mass.
Molecular mass from vapor density, colligative properties, or mass spectrometry.
Classification of Organic Compounds
Based on carbon skeleton: Acyclic (open chain), Cyclic (closed chain: alicyclic, aromatic).
Based on functional groups: Alkanes, alkenes, alcohols, etc.
Nomenclature of Organic Compounds
IUPAC system: Root word + prefix + suffix.
Rules
CH₃CH₂CH₃: Propane
CH₃CH=CH₂: Propene
CH₃CH₂OH: Ethanol
Cyclic and Aromatic
JEE Main Weightage
This chapter typically carries 2-3 questions in JEE Main, covering purification methods, element detection, and IUPAC naming.
Tips & Tricks
Key Points for JEE Main
- Master Lassaigne's test observations
- Practice IUPAC naming for complex molecules
- Understand purification choice based on compound nature
- Remember formulas for % calculation