Are aliphatic hydrocarbons reactive?

Alkanes: Less reactive due to their strong sigma bonds, Alkenes and alkynes: More reactive due to the presence of double and triple bonds, which can participate in addition and polymerization reactions.

How do aliphatic hydrocarbons differ from aromatic hydrocarbons?

Aliphatic hydrocarbons lack a benzene ring or aromatic system, whereas aromatic hydrocarbons contain at least one benzene ring and exhibit resonance stability.

Why are aliphatic hydrocarbons important?

They are fundamental to the petrochemical industry, forming the basis for fuels, plastics, lubricants, and synthetic fibers.

What are cycloalkanes, and are they aliphatic?

Cycloalkanes are cyclic aliphatic hydrocarbons with single bonds, such as cyclopropane and cyclohexane. They are saturated hydrocarbons.

Aliphatic Hydrocarbons: Types, Properties, Uses

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JEE Chemistry

Aliphatic Hydrocarbons

1.0What are Aliphatic Hydrocarbons

Aliphatic hydrocarbons are organic compounds composed of hydrogen and carbon atoms arranged in straight chains, branched chains, or non-aromatic rings. They are distinct from aromatic hydrocarbons, which contain benzene-like rings.

2.0Types of Aliphatic Hydrocarbons

There are mainly 3 parts of Aliphatic Hydrocarbon-

Alkanes: Saturated hydrocarbons containing only single bonds known as alkanes.

General Formula: C_nH_2n+2
Examples: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈).

Alkenes: Unsaturated hydrocarbons containing at least one carbon-carbon double bond known as alkenes.

General Formula: C_nH_2n
Examples: Ethene (C₂H₄), Propene (C₃H₆).

Alkynes: Unsaturated hydrocarbons containing at least one carbon-carbon triple bond known as alkynes.

General Formula: C_nH_2n−2
Examples: Ethyne (C₂H₂), Propyne (C₃H₄).

3.0Examples of Aliphatic Hydrocarbons

Type	Definition	Examples	Formula	Uses
Alkanes (Saturated)	Single bonds between carbon atoms.	Methane	CH₄	Natural gas, fuel for heating.
		Ethane	C₂H₆	Feedstock for ethylene production.
		Propane	C₃H₈	Fuel for cooking and heating.
		Butane	C₄H₁₀	Used in lighters and refrigerants.
Alkenes (Unsaturated)	At least one carbon-carbon double bond.	Ethene (Ethylene)	C₂H₄	Plastic production (polyethylene).
		Propene	C₃H₆	Manufacturing polypropylene plastics.
		Butene	C₄H₈	Used in rubber production.
Alkynes (Unsaturated)	At least one carbon-carbon triple bond.	Ethyne (Acetylene)	C₂H₂	Welding and cutting metals.
		Propyne	C₃H₄	Intermediate in organic synthesis.
		Butyne	C₄H₆	Used in organic compound synthesis.
Cycloalkanes	Cyclic saturated hydrocarbons.	Cyclopropane	C₃H₆	Used as an anesthetic.
		Cyclobutane	C₄H₈	Found in natural gas.
		Cyclohexane	C₆H₁₂	Used in nylon production.
Branched Alkanes	Alkanes with side chains or branches.	Isobutane	C₄H₁₀	Refrigerants and propellants.
		Isohexane	C₆H₁₄	Gasoline component.
Long-Chain Alkanes	Hydrocarbons with long carbon chains.	Decane	C₁₀H₂₂	Diesel fuels.
		Hexadecane	C₁₆H₃₄	Lubricants and fuels.

4.0Properties of Aliphatic Hydrocarbons

Property	Description
Boiling/Melting Point	Generally increase with molecular weight; influenced by chain length and branching.
Solubility	Insoluble in water but soluble in organic solvents like benzene and ether.
Flammability	Highly flammable, producing carbon dioxide and water upon complete combustion.

5.0Differences Between Aliphatic and Aromatic Hydrocarbons

Property	Aliphatic Hydrocarbons	Aromatic Hydrocarbons
Structure	Straight/branched chains, or cyclic (non-aromatic).	Contain benzene-like rings.
Reactivity	Alkenes/alkynes more reactive than alkanes.	Undergo substitution rather than addition.
Examples	Methane, Ethene, Ethyne.	Benzene, Naphthalene.

6.0Applications of Aliphatic Hydrocarbons

Fuel: Methane, propane, and butane are widely used as energy sources.
Industrial Chemicals: Ethylene and acetylene are used in polymer production and welding, respectively.
Solvents: Hexane and other alkanes are used in industrial cleaning and extraction processes.
Building Blocks: Serve as precursors in synthesizing plastics, detergents, and pharmaceuticals.

7.0Reactions Involving Aliphatic Hydrocarbons

Combustion Reaction: Aliphatic hydrocarbons react with oxygen to produce carbon dioxide (CO₂) and water (H₂O). This is a highly exothermic reaction and is the basis for their use as fuels.

Ex. $C H_{4} + 2 O_{2} \to C)_{2} + 2 H_{2} O$

Substitution (For Alkanes): In alkanes, a hydrogen atom is replaced by a halogen atom in the presence of UV light or a catalyst. This is called a substitution reaction and is typical of saturated hydrocarbons.

Ex. $C H_{4} + C l_{2} U V L i g h t C H_{3} Cl + H Cl$ (Chlorination of methane)

Addition (For Alkenes and Alkynes): Due to their unsaturated nature, alkenes and alkynes undergo addition reactions. Molecules like hydrogen (H₂), halogens (Cl₂, Br₂), or hydrogen halides (HCl, HBr) can add across their double or triple bonds, converting them into saturated hydrocarbons.

$C H_{4} + H_{2} C a t a l ys t C_{2} H_{6}$ (Hydrogenation of ethene)

$C_{2} H_{2} + B r_{2} \to C_{2} H_{2} B r_{2}$ (Bromination of ethyne)

Halogenation: Alkenes and alkynes react with halogens like Cl₂ or Br₂, adding halogen atoms across their double or triple bonds.

$C_{2} H_{4} + B r_{2} \to C_{2} H_{4} B r_{2}$ (Bromination of ethene)

8.0Summary of Aliphatic Hydrocarbon

Reaction Type	Description	Example
Combustion	Reaction with oxygen to form CO₂ and H₂O.	CH₄+ 2O₂ → CO₂ + 2H₂O
Substitution	Replacement of H in alkanes with halogens.	CH₄+Cl₂ → CH₃Cl + HCl (in UV light).
Addition	Alkenes/alkynes react with H₂, Cl₂, or Br₂.	C₂H₄+ H₂→ C₂H₆.
Polymerization	Formation of long-chain polymers from alkenes.	n(C₂H₄) → (−CH₂−CH₂−)n (Polyethylene)

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