Ch 13Hydrocarbons — Class 11 Chemistry, concept-first.

Objectives After studying this unit, you should be able to: - name hydrocarbons according to the IUPAC system of nomenclature; - recognise and write structures of isomers of alkanes, alkenes, alkynes…

Hydrocarbons are the simplest organic compounds — they contain only carbon and hydrogen. But the way those carbon atoms link to each other changes everything.

Alkanes are the simplest family of organic compounds. They are saturated, open-chain (acyclic) hydrocarbons — meaning every carbon atom is bonded to four other atoms (all single bonds), and the carbon…

The first three alkanes — methane (), ethane (), and propane () — each exist as only one structure. There is exactly one way to arrange the carbon atoms in each case.

Petroleum and natural gas are the primary natural sources of alkanes. In the laboratory, alkanes can be prepared by several distinct methods, each useful for specific types of alkanes.

Alkanes are almost non-polar molecules. The C–C and C–H bonds are covalent, and the electronegativity difference between carbon and hydrogen is very small.

The foundation of alkane structure is the tetrahedral geometry of carbon. In methane, the simplest alkane, the carbon atom sits at the centre of a regular tetrahedron with its four hydrogen atoms at t…

Alkenes form a family of unsaturated hydrocarbons. The defining structural feature of every alkene is the presence of at least one carbon–carbon double bond ().

The carbon-carbon double bond is not simply two identical bonds stacked on top of each other. It is a hybrid structure built from two very different types of bonds: one strong sigma () bond and one we…

When you name an alkene, the first rule is that the double bond determines everything — the chain you choose, the numbering you use, and the suffix you attach.

Alkenes exhibit two distinct types of isomerism: structural isomerism and geometrical isomerism. This arises because the carbon-carbon double bond is both a site of branching (like alkanes) and a rigi…

Alkenes are prepared by four main methods in the laboratory. Each method gives you control over the structure and sometimes even the geometry of the double bond formed.

Alkenes share many physical characteristics with alkanes, though they differ in isomerism and polarity. The first three alkenes — ethene, propene, and butene — are gases at room temperature.

Alkynes are unsaturated hydrocarbons that contain at least one carbon‑carbon triple bond. Because a triple bond uses three pairs of electrons, each triple bond reduces the number of hydrogen atoms by…

In the older common system, alkynes are named as derivatives of acetylene (). For example, is called methylacetylene. This system is simple but becomes unwieldy for larger molecules.

The simplest alkyne is ethyne, . Its structure reveals the fundamental nature of the carbon-carbon triple bond. Each carbon atom in ethyne is sp-hybridised.

Alkynes, particularly ethyne (acetylene), are prepared on both industrial and laboratory scales. The textbook describes two principal methods.

The physical properties of alkynes follow the same general trends observed in alkenes and alkanes. The first three members (ethyne, propyne, and but-1-yne) are gases at room temperature.

The word "aromatic" comes from the Greek aroma, meaning pleasant smell. Early chemists gave this name because many of these compounds — benzene, toluene, naphthalene — had distinctive, often sweet odo…

The naming system for aromatic hydrocarbons follows the same IUPAC rules you studied in Unit 8. For benzene derivatives, the parent name is "benzene," and substituents are named as prefixes.

Benzene was first isolated by Michael Faraday in 1825. Its molecular formula, , immediately signals a problem: the molecule is highly unsaturated — compare it to the saturated alkane — yet it does not…

The word "aromatic" originally came from the strong, pleasant smells of compounds like benzene. But as chemists studied these molecules more deeply, they realised the fragrance was a side effect of a…

Benzene is the simplest aromatic hydrocarbon. In industry, it is obtained from coal tar — a byproduct of the destructive distillation of coal.

Aromatic hydrocarbons are non-polar molecules. This non-polar nature governs nearly all their physical behaviour.

When a benzene ring already carries one substituent (a functional group), the position where a second substituent enters is not random.

Benzene and polynuclear hydrocarbons — compounds with more than two benzene rings fused together — are toxic and possess cancer-producing (carcinogenic) properties.

- Alkanes (): Saturated hydrocarbons with only single bonds. Key reactions: free-radical halogenation (e.g., ) and combustion (). Conformation of ethane: staggered (more stable) vs.

The unit closes with the NCERT's own end-of-chapter exercises (9.1–9.25), each answered below with our own worked solutions.

Higher-order thinking / exemplar-style practice problems.