How are alkenes different from alkanes?

Alkenes have one or more double bonds, while alkanes have only single bonds.Alkenes are more reactive than alkanes due to the presence of the π bond in the double bond.

Why are alkenes called unsaturated hydrocarbons?

They are called unsaturated because they have double bonds and can add more atoms (like H₂, Br₂, etc.) across the double bond.

What are electrophilic addition reactions in alkenes?

Alkenes undergo electrophilic addition reactions, where an electrophile attacks the π bond of the alkene. Common reactions include: Hydrogenation, Halogenation, Hydrohalogenation, Hydration

What is Markovnikov’s rule?

In the addition of HX to an unsymmetrical alkene, the hydrogen atom adds to the carbon with more hydrogen atoms already present, and the halogen adds to the carbon with fewer hydrogen atoms.

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Alkene

Alkenes are a family of unsaturated hydrocarbons that contain at least one carbon–carbon double bond (C=C). This double bond plays a crucial role in determining the chemical behavior of these compounds. While not abundantly found in crude oil, alkenes are primarily produced by cracking alkanes during petroleum processing.

1.0Introduction to Alkenes

Alkenes, particularly ethene, are extremely important in the chemical industry. Although they are hydrocarbons like alkanes, their double bond makes them more reactive. Alkenes are essential for manufacturing plastics and many other chemicals. Despite being combustible, they are rarely used as fuels because they are far more valuable as chemical feedstocks.

2.0Naming Alkenes using IUPAC rules

Find the longest carbon chain containing the double bond.
Number the chain from the end nearest to the double bond.
Use the suffix -ene and indicate the position of the double bond. Example: But-2-ene, Pent-1-ene

3.0General Properties of Alkenes

Property	Details
Physical State	C2–C4: Gases, C5–C17: Liquids, C18+: Solids at room temperature.
Density	Alkenes are lighter than water.
Solubility	Insoluble in water, but soluble in organic solvents like benzene.
Boiling Point	Boiling points increase with molecular mass, due to stronger van der Waals forces.
Combustion	Burn in air with a luminous, smoky flame. Ethene burns explosively in pure oxygen.

4.0Classification of Alkenes

Alkenes are classified based on the number of alkyl groups attached to the sp²-hybridized carbon atoms of the double bond. This classification helps determine the stability and reactivity of alkenes.

Type	Structure	Example
Monosubstituted	RCH=CH₂	Propene
Disubstituted	RCH=CHR or R₂C=CH	But-2-ene
Trisubstituted	R₂C=CHR	2-Methylbut-2-ene
Tetrasubstituted	R₂C=CR₂	2,3-Dimethylbut-2-ene

5.0Uses of Alkenes

Alkenes are versatile and widely used in various industrial and commercial applications:

Ethene (Ethylene)

Used to manufacture polyethylene (polythene) for bags, bottles, containers, etc.
Helps produce ethanol and ethylene glycol (used as antifreeze).

Propene (Propylene)

Used in the production of polypropylene, ropes, packaging materials.
Precursor to propanol, which is used to manufacture acetone.

Styrene (from alkenes)

Used in making polystyrene, found in car battery cases and refrigerator parts.

Terylene (from alkenes)

A synthetic polyester fiber used in textiles.

Other Applications

Used in producing anti-knock agents for petrol engines.
Manufacture of acrylic fibers for textiles and upholstery.