# Hydrocarbons Notes, Class 11 Chemistry | SwaVid

Hydrocarbons, NCERT Class 11 Chemistry: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers.

Canonical: https://www.swavid.com/cbse/class-11/chemistry/chapter/hydrocarbons

Source: https://www.swavid.com/cbse/class-11/chemistry/chapter/hydrocarbons

# Hydrocarbons

## Formulas and definitions

## Key ideas

## Common mistakes

## Quick checks

## Keep going

## Questions parents ask

## Class 11 Chemistry on SwaVid

### Classification and nomenclature of hydrocarbons

### Alkanes and their conformations

### Alkenes and geometrical isomerism

### Addition reactions of alkenes

### Alkynes and their acidic character

### Aromaticity and electrophilic substitution

### Related chapter

### Related chapter

### Related chapter

### All chapters

SwaVid › CBSE › Class 11 › Chemistry › Hydrocarbons

Notes written by SwaVid from the NCERT textbook.

Class 11 Chemistry, Unit 9. Key ideas, formulas and common mistakes.

CBSE prints 10 marks for Unit 9, not for this chapter alone.

Short answer. This chapter covers the classification, preparation, properties, and reactions of alkanes, alkenes, alkynes, and aromatic hydrocarbons. It explains fundamental reaction mechanisms including free radical substitution, electrophilic addition, and electrophilic aromatic substitution.

Source: NCERT Chemistry Part II (Reprint 2026-27) , Unit 9, Hydrocarbons

Hydrocarbons are compounds composed solely of carbon and hydrogen, grouped into open-chain and cyclic types. Open-chain compounds include saturated alkanes and unsaturated alkenes and alkynes, while cyclic compounds include alicyclic and aromatic hydrocarbons.

Alkanes are relatively unreactive open-chain saturated hydrocarbons that undergo free radical halogenation, combustion, and aromatisation. Rotation around the carbon-carbon single bond produces conformational isomers like eclipsed and staggered forms, with the staggered form being the most stable due to minimum torsional strain.

Alkenes possess a carbon-carbon double bond consisting of one strong sigma bond and one weaker pi bond. Restricted rotation around the double bond leads to cis-trans isomerism when each double-bonded carbon bears two distinct groups.

Alkenes primarily undergo electrophilic addition reactions across the pi bond. Addition of unsymmetrical reagents like HBr follows Markovnikov's rule, but the addition shifts to anti-Markovnikov regioselectivity in the presence of organic peroxides.

Alkynes contain a carbon-carbon triple bond with two mutually perpendicular pi bonds. The hydrogen atoms attached to sp-hybridised triply-bonded carbon atoms are weakly acidic and can be replaced by active metals like sodium.

Aromatic compounds are planar, cyclic conjugated systems containing (4n + 2) pi electrons according to Hückel's rule. Benzene and its derivatives typically undergo electrophilic aromatic substitution reactions such as nitration, halogenation, sulphonation, and Friedel-Crafts alkylation or acylation.

Try each question first. Then tap it to see the answer.

General combustion formula: CₙH₂ₙ₊₂ + ((3n + 1) / 2) O₂ → n CO₂ + (n + 1) H₂O

For butane, n = 4

Moles of O₂ = (3(4) + 1) / 2 = 13 / 2 = 6.5

6.5 moles

Set up the Hückel condition: 4n + 2 = 8 pi electrons

4n = 6, which gives n = 1.5

Since n must be an integer (0, 1, 2, ...), 8 pi electrons fails Hückel's rule and the ring is non-aromatic

Not aromatic

Propene is an unsymmetrical alkene: CH₃-CH=CH₂

Presence of peroxide causes free radical addition following anti-Markovnikov regioselectivity

The bromine radical attacks the terminal carbon first, placing the hydrogen on the middle carbon to form 1-bromopropane

1-bromopropane

Organic Chemistry - Some Basic Principles and Techniques .

Chemical Bonding and Molecular Structure .

Thermodynamics .

The 9 chapters of Class 11 Chemistry .

CBSE does not give marks to one chapter. It prints 10 marks for Unit 9, Hydrocarbons, which includes Hydrocarbons.

No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed.

This is the last chapter in the NCERT books for Class 11 Chemistry.

SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works.

- Unit 9 NCERT book
- 10 marks, Unit 9
- 3 quick checks
- Applying the peroxide effect to HCl or HI additions . Use the peroxide effect only for HBr additions. The H-Cl bond is too strong to be broken by radical intermediates, and the H-I reaction is not energetically favourable because iodine radicals recombine into I₂.
- Assuming all terminal alkynes and alkenes show acidic character . Only terminal alkynes have an sp-hybridised carbon with 50% s-character, making the C-H bond acidic enough to liberate hydrogen gas with sodium. Alkene and alkane hydrogens are not sufficiently acidic for this reaction.
- Using the Wurtz reaction to prepare alkanes with odd numbers of carbon atoms . Use the Wurtz reaction primarily for symmetrical alkanes with an even number of carbon atoms. Mixing two different alkyl halides produces an inseparable mixture of three distinct alkanes.
- Counting all cyclic conjugated rings as aromatic regardless of electron count . Apply Hückel's rule specifically by checking that the molecule is cyclic, planar, fully conjugated, and has exactly (4n + 2) pi electrons, not 4n pi electrons.

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