Unit 2: Alkanes, Alkenes and Conjugated Dienes 

February 20, 2026

Semester 2
BP202T

Introduction to Alkanes, Alkenes and Conjugated Dienes

Unit 2 covers the chemistry of the most basic carbon compounds. You will study the structure (hybridization) and reactivity of Alkanes and Alkenes. Critically, you will learn about Elimination Reactions (E1 & E2), the famous Markownikoff’s Rule, and the unique chemistry of Conjugated Dienes including the Diels-Alder reaction.

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Syllabus & Topics

  • 1SP3 hybridization in Alkanes: Structure and geometry.
  • 2Halogenation of Alkanes: Free radical substitution mechanism.
  • 3Stability and Uses of Paraffins.
  • 4Stability of Alkenes: SP2 hybridization.
  • 5E1 Reactions: Kinetics, order of reactivity, rearrangement of carbocations, Saytzeff’s orientation and evidences.
  • 6E2 Reactions: Kinetics, order of reactivity of alkyl halides.
  • 7E1 vs E2 Reactions: Comparison and factors affecting.
  • 8Ozonolysis of Alkenes.
  • 9Electrophilic Addition Reactions of Alkenes and Markownikoff’s Orientation.
  • 10Free Radical Addition Reactions of Alkenes and Anti-Markownikoff’s Orientation.
  • 11Stability of Conjugated Dienes.
  • 12Diel-Alder Reaction of Conjugated Dienes.
  • 13Electrophilic and Free Radical Addition Reactions of Conjugated Dienes.
  • 141,2-addition vs 1,4-addition (Allylic Rearrangement).

Learning Objectives

Explain Halogenation: Write the mechanism (3 steps) of free radical halogenation of methane.
Apply Saytzeff’s Rule: Predict the major product of an E2 elimination reaction.
Apply Markownikoff’s Rule: Predict the major product of HX addition to an unsymmetric alkene.
Distinguish E1 vs E2: Give the conditions that favor E1 vs E2 reactions.
Explain Diels-Alder: Draw the products of a given Diene + Dienophile reaction.

Frequently Asked Questions (FAQs)

Q1. What is Markownikoff’s Rule?

Markownikoff’s Rule states that when a hydrogen halide (HX) adds to an unsymmetrical alkene, the hydrogen (H) attaches to the carbon atom that already has more hydrogen atoms, and the halide (X) attaches to the carbon with more alkyl substituents.

Q2. What is Anti-Markownikoff’s addition?

Anti-Markownikoff addition occurs in free radical reactions. In the presence of peroxides or UV light, HBr adds in the opposite orientation: hydrogen attaches to the more substituted carbon, and bromine attaches to the less substituted carbon.

Q3. What is Saytzeff’s Rule?

Saytzeff’s Rule (Zaitsev’s Rule) states that in E1 and E2 elimination reactions, the major product formed is the more substituted (and more stable) alkene.

Q4. What are the conditions for E2 vs E1?

  • E2 reaction: Requires a strong, often bulky base, occurs in one step, and is a bimolecular reaction.

  • E1 reaction: Requires a polar protic solvent and a weak base, proceeds in two steps via a carbocation intermediate.

Q5. What is the Diels–Alder Reaction?

The Diels–Alder reaction is a [4+2] cycloaddition reaction between a conjugated diene (4 π electrons) and a dienophile (2 π electrons), forming a six-membered ring.