What are Alkenes?
Alkenes are the most common type of hydrocarbon found in crude oil. There is at least one carbon-carbon double bond in this family. This double bond significantly alters the chemistry of the family’s compounds.
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Alkenes, and ethene in particular, are crucial to the chemical industry. They are not found in large quantities in crude oil but are produced by cracking the alkanes. As with all hydrocarbons, alkenes burn in air to produce carbon dioxide and water. Ethene reacts explosively with oxygen, making it a poor fuel. Additionally, alkenes are too useful in the chemical industry for the production of plastics and numerous other chemicals to be utilized as fuels.
General Properties of Alkenes
- Physical state – Members containing two or four carbon atoms are gases, five to seventeen, liquids, eighteen and beyond, and solids at room temperature; they burn with a luminous, smoky flame in air.
- Alkenes have a lower density than water.
- Alkenes are insoluble in water, but soluble in organic solvents like benzene, etc.
- Boiling point – The boiling points of alkenes increase gradually with increasing molecular mass or chain length, indicating that intermolecular attractions become stronger as the size of the molecule increases.
Classification of Alkenes
Alkyl groups bonded to the sp2 hybridized carbon atoms of alkenes influence the double bond’s stability. Alkenes’ chemical reactivity is frequently influenced by the number of alkyl groups bonded to their sp2 hybridized carbon atoms. Consequently, it is advantageous to classify alkenes according to the number of alkyl groups attached to the C=C structural unit. This characteristic is known as the degree of substitution.
Monosubstituted alkenes have a single alkyl group attached to the sp2 hybridized carbon atom of the double bond. Terminal alkene refers to an alkene whose double bond is at the end of the chain of carbon atoms. Alkenes with two, three, or four alkyl groups bonded to the double bond’s carbon atoms are disubstituted, trisubstituted, or tetrasubstituted, respectively.
| monosubstituted | RCH=CH2 |
| disubstituted | RCH=CHR or R2C=CH |
| trisubstituted | R2C=CHR |
| tetrasubstituted | R2C=CR2 |
Uses of Alkenes
Below is a list of applications for various alkenes such as ethene, propene, etc.
- Producing plastics such as polythene for the production of buckets, bowls, bags, etc.
- The production of polystyrene is used to create automobile battery cases and refrigerator components.
- Antifreeze ethane-1,2-diol production for automobile radiators.
- The production of ethanol and synthetic fiber terylene.
- Creating an anti-knock for automobile engines.
- Production of plastic, and polypropene, for use in ropes and packaging.
- Production of propanol for acetone production.
- Synthesis of acrylic fibers.
Frequently Asked Questions on Alkenes
Q.1 What purpose do alkenes serve?
Alkenes have a wide range of applications in manufacturing. They are used as starting materials in the synthesis of alcohols, plastics, lacquers, detergents, and fuels. The most important alkenes for the chemical industry are ethene, propene, and 1,3-butadiene.
Q.2 Where can you find alkene?
Alkenes are the raw materials for a variety of plastics, including polyethene, PVC, polypropylene, and polystyrene. Unsaturated fatty acids, beta-carotene, and visible light all contain alkenes.
Q.3 What characteristics define alkenes?
Alkenes and alkanes share similar physical properties: they are colorless, nonpolar, and combustible. At room temperature, alkenes exist in all three phases: solids, liquids, and gases. However, isomers of cis alkenes have lower melting points than trans isomers.
Q.4 Have higher boiling points alkenes?
With increasing intermolecular mass, the boiling point increases. With increasing molecule size, the intermolecular forces of alkenes become stronger. In each case, the alkene’s boiling point is a small number of degrees lower than that of the corresponding alkane.
Q.5 Can alkenes function as a fuel?
Alkenes, unlike alkanes, readily burn to produce carbon dioxide and water if, for instance, the combustion is complete. Despite two factors, they are NOT utilized as fuels. For the production of plastics, antifreeze, and a variety of other useful compounds, they are far too expensive to use.
Q.6 How is an alkene analyzed?
Bromine water is used as an alkene test. If an alkene is shaken with bromine water, the solution becomes colorless (or bubble a gaseous alkene through bromine water). Alkenes decolourise bromine water.
Q.7 What reactions do alkenes undergo?
Alkenes are relatively stable compounds, but due to the carbon-carbon -bond reactivity, they are more reactive than alkanes. Most alkene reactions involve forming new single bonds by adding to this bond. Carbon-carbon double bonds in alkenes such as ethene react with concentrated sulphuric acid.
Q.8 Why do alkanes have the name paraffin?
The word paraffins comes from the Latin language. Alkanes are referred to as paraffins due to their low affinity with a general reagent. Alternatively, alkanes are toxic substances. They undergo reactions only under extreme conditions.
