NCERT Handwritten Notes Alkene [ Pdf Download ]
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What are Alkenes?
The alkenes are a prevalent hydrocarbon family found in crude oil. There is at least one carbon–carbon double bond in this family. This double bond has a significant impact on the chemistry of the family’s molecules.
In the chemical industry, alkenes, notably ethene, are extremely important. They are formed by the cracking of alkanes and are not found in considerable concentrations in crude oil. Alkenes, like all hydrocarbons, burn in the presence of oxygen to produce carbon dioxide and water. Because ethene reacts explosively in oxygen, it is ineffective as a fuel. Alkenes are too useful in the chemical industry for the production of plastics and a variety of other compounds to be utilised as fuels.
General Properties of Alkenes
- Physical state – Gases from five to seventeen, liquids from eighteen onwards, and solids at room temperature are the members with two or four carbon atoms, and they burn in air with a bright smoky flame.
- Density – Alkenes have a lower density than water.
- Solubility – Alkenes are water-insoluble but soluble in organic solvents like benzene.
- Boiling point – The boiling temperatures of alkenes gradually increase as the molecular mass or chain length increases, indicating that the intermolecular interactions become stronger as the molecule grows larger.
Classification of Alkenes
The stability of the double bond is affected by alkyl groups attached to the sp2 hybridized carbon atoms of alkenes. The number of alkyl groups linked to the sp2 hybridized carbon atoms can also alter the chemical reactivity of alkenes. As a result, alkenes can be classified according to the number of alkyl groups connected to the C=C structural unit. The degree of substitution is the term for this attribute.
Monosubstituted alkenes have a single alkyl group linked to the sp2 hybridized carbon atom of the double bond. A terminal alkene is an alkene with a double bond at the end of the carbon atom chain. Disubstituted, trisubstituted, and tetrasubstituted alkenes have two, three, or four alkyl groups attached to the carbon atoms of the double bond, respectively.
| Monosubstituted | RCH=CH2 |
| Disubstituted | RCH=CHR or R2C=CH |
| Trisubstituted | R2C=CHR |
| Tetrasubstituted | R2C=CR2 |
Use of alkenes
The usage of various alkenes such as ethene, propene, and others are listed below.
- Manufacturing of plastics such as polythene for buckets, bowls, and bags, among other things.
- Polystyrene is a type of plastic that is used to make automobile battery housing and refrigerator parts.
- Ethane-1,2-diol is used as an anti-freeze in automobile radiators.
- Production of ethanol and terylene, a synthetic fiber.
- Making an anti-knock system for automobile engines.
- Plastic and polypropene manufacturing for ropes and packaging materials.
- Propanol is a chemical that is used to make acetone.
- Fabrication of acrylic fibers.
Frequently Asked Questions on Alkenes
What are alkenes used for?
Alkenes are used in a variety of ways in the manufacturing industry. They are utilised as starting materials in the production of alcohols, polymers, lacquers, detergents, and fuels. The most important alkenes in the chemical industry are ethene, propene, and 1,3-butadiene.
Where is alkene found?
Thermal cracking of ethane can result in the generation of ethene and a hydrogen molecule. Plastics such as polyethene, PVC, polypropylene, and polystyrene, among others, are made from alkenes. Alkene chemistry can be found in unsaturated lipids, beta-carotene, and light transmitted through eyesight.
What are the characteristics of alkenes?
Alkenes and alkanes have some physical qualities, such as being colourless, nonpolar, and flammable. The molecular mass determines the physical state: At normal temperature, gases resemble the simplest alkenes, ethene, propene, and butene, which are saturated hydrocarbons.
Do alkenes have higher boiling points?
The greater the boiling point, the more intermolecular mass there is. The intermolecular forces of alkenes become greater as the size of the molecules increases. The boiling point of the alkene is a few degrees lower than that of the comparable alkane in each case.
Can alkenes be used as fuel?
Alkenes, unlike alkanes, burn rapidly to produce carbon dioxide and water if the combustion is complete, for example. However, they are not employed as fuels for two reasons. They are significantly too valuable to be used in the production of plastics, antifreeze, and a variety of other useful substances.
How do you test for an alkene?
As an alkene test, bromine water is used. When you shake an alkene with bromine water, the solution becomes colourless (or bubble a gaseous alkene through bromine water). Bromine water is discoloured by alkenes.
How do alkenes react?
Alkenes are typically stable molecules, although their carbon-carbon -bond reactivity makes them more reactive than alkanes. The majority of alkene reactions involve adding to this bond, resulting in the formation of new single bonds. The carbon-carbon double bond reacts with concentrated sulfuric acid in alkenes like ethene.
Why are alkanes called paraffins?
The word “paraffins” comes from the Latin language. Because alkanes have a poor affinity for a general reagent, they are referred to as paraffins. Alkanes are poisonous chemicals, to put it another way. They have reactions only under extreme circumstances.
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