Lesson Plan: Hydrocarbons

Organic Chemistry

Hydrocarbons

This chapter applies the logic of GOC to real molecules: Alkanes, Alkenes, Alkynes, and Benzene. It introduces the "Named Reactions" (Wurtz, Friedel-Crafts) that you will see repeatedly in Class 12.

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⚠️ Prerequisites

GOC (Crucial): Stability of Carbocations (for Markovnikov rule).
Isomerism: Geometrical (cis/trans) and Conformational (Newman projections).
Resonance: To understand Ortho/Para directors in Benzene.

🧠 Study Approach

Reaction Maps: Do not memorize reactions in a list. Create "Roadmaps": Start with Ethane, how do you get to Ethene? To Ethyne? To Benzene? Connect the dots.

Study Sequence

1. Alkanes ($C_nH_{2n+2}$)

Preparation: Wurtz Reaction (Coupling), Decarboxylation (Soda-lime), Kolbe's Electrolysis.
Properties: Free Radical Halogenation mechanism (Initiation, Propagation, Termination). Conformational Isomerism (Staggered vs Eclipsed).

2. Alkenes ($C_nH_{2n}$) - Prep & Structure

Structure of double bond. Geometrical Isomerism.
Preparation: From Alkynes (Lindlar's vs Na/Liq $NH_3$), Dehydration of Alcohols, Dehydrohalogenation ($\beta$-Elimination, Saytzeff Rule).

3. Alkenes - Properties (CRITICAL)

Electrophilic Addition: Markovnikov's Rule (Add H to C with more H). Anti-Markovnikov (Peroxide Effect - only HBr).
Ozonolysis: Reductive ($Zn/H_2O$) vs Oxidative. Locating double bond position.

4. Alkynes ($C_nH_{2n-2}$)

Acidic Nature: Terminal H is acidic (reacts with Na, Sodamide).
Reactions: Addition of water ($Hg^{2+}/H^+$) to form Ketones/Aldehydes. Cyclic Polymerization to Benzene.

5. Aromatic Hydrocarbons (Benzene)

Hückel's Rule: $(4n+2)\pi$ electrons + Planar + Conjugated.
EAS Mechanism: Electrophilic Aromatic Substitution. Nitration, Sulphonation, Halogenation, Friedel-Crafts (Alkylation & Acylation).

6. Directive Influence & Carcinogenicity

Ortho/Para directors (Activators) vs Meta directors (Deactivators). Why $-NO_2$ directs meta but $-CH_3$ directs ortho/para. Toxicity of PAHs.

🎯 How to Practice

The "Missing Reagent" Game: Write down reactants and products (e.g., Benzene $\to$ Nitrobenzene) and test yourself on the reagent needed (Conc $HNO_3 + H_2SO_4$).

Mechanism Practice: Draw the sigma-complex (arenium ion) resonance structures for Electrophilic Aromatic Substitution. This explains the directive influence.

Ozonolysis Reverse Engineering: Given products (e.g., Ethanal + Methanal), draw the structure of the original alkene.

📝 Quick Revision Notes

Key Rules

Markovnikov: Negative part to C with less H.
Saytzeff: More substituted alkene is major product.
Hückel: $4n+2$ $\pi$-electrons = Aromatic.

Important Reagents

$Zn-Hg/HCl$: Clemmensen Reduction

$AlCl_3$: Friedel-Crafts Catalyst

$O_3/Zn$: Ozonolysis

$NaNH_2$: Strong Base (Alkynes)

Conformations (Ethane)

Staggered (More Stable) > Skew > Eclipsed (Least Stable)

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