NCERT Solutions for Class 11 Chemistry Chapter 13 - Hydrocarbons
Hydrocarbons are the backbone of organic chemistry, and Chapter 13 is where everything learned in Chapter 12 gets applied for the first time. The classification of hydrocarbons into alkanes, alkenes, alkynes, and arenes, along with their preparation, physical properties, and chemical reactions, makes this chapter quite content-heavy. Students often find it difficult to predict the major product of an addition reaction or to explain why benzene undergoes electrophilic substitution rather than addition.
The NCERT solutions for Class 11 Chemistry Chapter 13 Hydrocarbons on Myclass24 make these concepts much easier to handle. Each mechanism - free radical halogenation, electrophilic addition, electrophilic aromatic substitution - is explained in a step-by-step manner. The solutions are accurate, board-pattern aligned, and include all the named reactions and mechanisms that appear in exams. If organic chemistry has been your weak area, this chapter's solutions from Myclass24 are a great place to start rebuilding confidence.
Download NCERT Solutions for Class 11 Chemistry Chapter 13 Hydrocarbons PDF
Access the free PDF of NCERT Solutions for Class 11 Chemistry Chapter 13 Hydrocarbons on Myclass24. The PDF includes all NCERT exercise solutions with reaction mechanisms, Markovnikov rule examples, and aromatic chemistry explanations.
Chapter 13 Hydrocarbons - Concepts, Facts and Key Tables
Hydrocarbons are compounds containing only carbon and hydrogen atoms. Chapter 13 classifies them into saturated (alkanes) and unsaturated (alkenes, alkynes) open-chain compounds, plus aromatic hydrocarbons (arenes, dominated by benzene).
Alkanes (CnH2n+2) are saturated hydrocarbons. Their primary reactions are combustion and free-radical halogenation. In free-radical halogenation, the mechanism involves three steps: initiation (Cl2 splits to 2Cl by UV light), propagation (chain reaction producing HCl and the haloalkane), and termination (combination of radicals). Reactivity of halogens decreases: F2 > Cl2 > Br2 > I2. Conformational isomers of ethane (staggered most stable, eclipsed least stable) are also discussed. One can check out all chapters of NCERT Solutions for Class 11 Chemistry and all subjects of NCERT Solutions for Class 11 from the Myclass24 page.
Alkenes (CnH2n) undergo electrophilic addition reactions. Key reactions include addition of HX (Markovnikov rule: H adds to C with more H atoms), addition of H2O (hydration, acid-catalysed), addition of H2 (catalytic hydrogenation), addition of X2 (halogenation - decolourises bromine water, a test for unsaturation), ozonolysis (cleaves double bond), and oxidative cleavage by KMnO4.
Alkynes (CnH2n-2) have a triple bond (one sigma + two pi). Acetylene (ethyne, HC=CH) is the simplest alkyne. Terminal alkynes are weakly acidic (pKa ~25) because the sp-hybridised C-H bond is stronger, making H slightly more acidic. They react with NaNH2 to form sodium acetylide.
Benzene (C6H6) is the simplest arene with delocalised pi electrons over all 6 carbons (aromatic stabilisation energy approx. 150 kJ/mol). Benzene undergoes electrophilic aromatic substitution (EAS): halogenation (with Lewis acid catalyst), nitration (HNO3/H2SO4), sulphonation (fuming H2SO4), Friedel-Crafts alkylation, and Friedel-Crafts acylation. Activating groups (-OH, -NH2, -alkyl) are ortho/para directors; deactivating groups (-NO2, -COOH, -CHO) are meta directors (except halogens: deactivating but o/p directors).
Classification of Hydrocarbons
| Class | General Formula | Bond Type | Primary Reaction Type | Example |
| Alkane | CnH2n+2 | Single (sigma) | Free radical substitution | Methane, Ethane |
| Alkene | CnH2n | One double (sigma+pi) | Electrophilic addition | Ethene, Propene |
| Alkyne | CnH2n-2 | One triple (sigma+2pi) | Electrophilic addition | Ethyne, Propyne |
| Arene | C6H5- etc. | Delocalised pi system | Electrophilic substitution | Benzene, Toluene |
Markovnikov Rule - Examples
| Reaction | Markovnikov Product | Anti-Markovnikov (Peroxide effect) |
| Propene + HBr | 2-Bromopropane (major) | 1-Bromopropane (major) |
| But-1-ene + HCl | 2-Chlorobutane (major) | 1-Chlorobutane (major) |
| Ethene + H2O (H+) | Ethanol | Not applicable |
EAS Directing Effects of Substituents
| Substituent | Effect on Ring | Directing Effect | Examples |
| -OH, -OR | Activating (strong) | ortho/para | Phenol, Anisole |
| -NH2, -NHR | Activating (strong) | ortho/para | Aniline |
| -alkyl | Activating (mild) | ortho/para | Toluene |
| -X (halogen) | Deactivating (mild) | ortho/para | Chlorobenzene |
| -NO2, -CN | Deactivating (strong) | meta | Nitrobenzene |
| -COOH, -CHO | Deactivating (strong) | meta | Benzoic acid |
FAQs for NCERT Solutions Class 11 Chemistry Chapter 13 Hydrocarbons
Hydrocarbons are organic compounds composed entirely of carbon and hydrogen atoms. They are classified into alkanes, alkenes, alkynes, and aromatic hydrocarbons. Hydrocarbons serve as important fuels and raw materials for many industries. Understanding their structure, properties, and reactions is essential for studying organic chemistry. This chapter forms the basis for learning more complex organic compounds and reaction mechanisms.
Alkanes contain only single carbon-carbon bonds, alkenes contain at least one double bond, and alkynes contain at least one triple bond. These differences significantly affect their chemical properties and reactivity. Alkenes and alkynes are generally more reactive than alkanes due to the presence of multiple bonds. Understanding these distinctions helps students classify hydrocarbons and predict their reactions. This topic is commonly tested in examinations because it forms the foundation of organic chemistry.
Aromatic hydrocarbons are compounds containing one or more benzene rings with delocalized electrons. Benzene is the most common aromatic compound and exhibits unique stability due to resonance. Aromatic hydrocarbons are important in industries producing dyes, medicines, plastics, and perfumes. Understanding aromaticity helps students explain the structure and behavior of these compounds. Questions related to benzene and aromatic hydrocarbons frequently appear in chemistry examinations.
Hydrocarbons play a vital role in modern society as fuels, industrial raw materials, and components of numerous consumer products. Natural gas, petrol, diesel, and liquefied petroleum gas are all hydrocarbon-based fuels. Hydrocarbons are also used in the manufacture of plastics, synthetic fibers, detergents, and pharmaceuticals. Understanding their applications helps students appreciate the significance of organic chemistry in daily life and industrial development. This practical relevance makes hydrocarbons an important examination topic.