WBJEE – Organic Chemistry
Topic: General Organic Chemistry (GOC)
Purpose:
- Build a solid foundation in the language of organic chemistry.
- Master the nomenclature, functional groups, isomerism, key reactions, and basic spectroscopic techniques that recur in the WBJEE syllabus.
- Equip you with a worked example to see concepts applied, and a quick revision summary for last‑minute review.
Tip: Read each section once, then test yourself with the questions at the end of each subsection.
1. Simple Explanation
Organic chemistry is the chemistry of carbon‑based molecules.
Carbon’s ability to form four covalent bonds (tetra‑valency) gives rise to a vast array of stable structures—alkanes, alkenes, alkynes, aromatics, heterocycles, and many functional groups.
Key idea: Every organic molecule can be understood by
- Its framework (backbone)
- The functional groups attached to it
- Their relative positions and three‑dimensional arrangement
2. Key Points
| Section | What to Memorize | Why It Matters |
|---|---|---|
| 2.1 Nomenclature (IUPAC) | • Longest chain (parent). • Numbering rules (lowest set of locants). • Substituents, prefixes, suffixes. |
Correct naming is required for any molecular description on WBJEE. |
| 2.2 Functional Groups | • Alkanes – C–C single bonds. • Alkenes – C=C. • Alkynes – C≡C. • Alcohols – –OH. • Ethers – –O–. • Halides – –X. • Aldehydes – –CHO. • Ketones – –CO–. • Carboxylic acids – –COOH. • Esters – –COO–. • Amides – –CONH₂. • Aromatics – benzene ring. |
Functional groups dictate reactivity and the class of reactions the molecule can undergo. |
| 2.3 Isomerism | • Structural isomers (chain, position, functional). • Stereoisomers (geometric cis/trans, optical enantiomers). |
Isomerism influences physical properties, spectra, and reaction pathways. |
| 2.4 Basic Reaction Types | • Addition – alkenes/alkynes. • Substitution – SN1, SN2, E1, E2. • Elimination – E1, E2. • Oxidation–Reduction – e.g., oxidation of alcohols. • Elimination–Addition (e.g., Diels–Alder). |
Recognising reaction types is essential for mechanism questions. |
| 2.5 Mechanisms (General) | • Electrophilic (alkenes, aromatics). • Nucleophilic (halides, alcohols). • Radical (halogenation). |
Mechanistic insight explains why a product forms. |
| 2.6 Spectroscopy Basics | • IR – functional‑group fingerprints. • ¹H NMR – chemical shift, multiplicity, integration. • ¹³C NMR – chemical shift. • Mass Spectrometry – molecular ion, fragmentation. |
Spectra are the “DNA” of a molecule; they confirm structure. |
| 2.7 Common Reaction Conditions | • Acidic → protonation, carbocations. • Basic → deprotonation, alkoxides. • Oxidizing → peroxides, KMnO₄. • Reducing → NaBH₄, LiAlH₄. |
Knowing the right reagent/condition helps predict the outcome. |
3. Worked Example
Problem (Typical WBJEE)
Predict the major product of the following reaction and give the mechanism.
[ \ce{CH3-CH2-CH2-CH3 + ClCH2CH2Cl -> ?} ]
(Use NaOH as base, perform the reaction in ethanol.)
Step‑by‑Step Solution
| Step | What Happens | Explanation |
|---|---|---|
| 1. Identify reagents | 1‑,2‑Dichloroethane + NaOH (strong base) | NaOH can act as a nucleophile ((\ce{OH-})). |
| 2. Determine reaction type | Nucleophilic substitution (SN2) | Primary chloride, strong nucleophile → SN2 favored. |
| 3. Locate leaving group | Two chlorides on 1,2‑dichloroethane | Each can be displaced; both are primary. |
| 4. Predict product | 2‑Butene + 2 Cl⁻ | Two Cl⁻ leave, forming a double bond. |
| 5. Mechanism | 1. (\ce{OH-}) attacks the less hindered carbon of 1,2‑dichloroethane. 2. Bond to C–Cl breaks, giving a carbanion intermediate. 3. The carbanion eliminates (\ce{Cl-}) forming a double bond. |
This is an E2 elimination (concerted). |
Answer:
[
\ce{CH3-CH=CH-CH3 +