Alkenes-Nomenclature

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. The general formula for Alkenes C_nH_2n.

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.

Nomenclature of alkenes

The IUPAC system is commonly used to name alkenes. Alkenes follow the same laws as alkanes in terms of structure. The rules for alkene nomenclature are as follows.

Find the longest carbon chain including the double bond. The alkene’s parent name is derived from the IUPAC designation for an alkane with the same number of carbon atoms, with the exception that the -ane ending is replaced with -ene to indicate the presence of a double bond. The chemical is a pentene if the longest continuous chain of carbon atoms bearing a double bond has five carbon atoms.

Starting with the end closest to the double bond, count the carbon atoms in the longest continuous chain. As a result, the double bond between the second and third carbon atoms of the chain is numbered from right to left. (When counting the chain from left to right, the double bond is mistakenly placed between the third and fourth carbons).

The lower of the pair of numbers assigned to the double-bonded carbon atoms are placed in front of the name of the alkene to denote the position of the double bond. For example butene (C₄H₈)

Any substituent molecule or group is identified by its location and name. For instance, 5-chloro-2-hexene. Finally, the cis or trans conformation label can be applied if the right three-dimensional connection between the groups connected to the double bond carbons is known.

Physical properties of Alkene

Alkenes have a carbon-carbon double bond that affects their physical properties. Unsaturated carbon compounds with the general formula C_nH_2n are known as alkenes. Olefins are another name for these chemicals.

Alkenes are a class of hydrocarbons that exclusively include hydrogen and carbon and have a carbon-carbon double bond. The first two hydrocarbons are ethene and propene.

Physical state

In nature, these double-bonded compounds are colourless and odourless. The only exception is ethene, which is a colourless gas with a somewhat pleasant odour.

The first three members of the alkene family are gaseous, the following fourteen are liquids, and the remaining alkenes are solids.

Solubility

Because of their nonpolar properties, alkenes are insoluble in water. However, nonpolar solvents such as benzene, ligroin, and others make them soluble.

Boiling point

As the amount of carbon atoms in a compound grows, the boiling point of the compound rises.

When alkenes and alkanes are compared, it is discovered that their boiling points are practically identical, as though they are made up of the same carbon skeleton. Straight-chain alkenes, like alkanes, have a higher boiling point than branched-chain alkenes.

Melting point

The melting temperatures of these double-bonded compounds are determined by how the molecules are arranged. Alkenes have a melting point that is similar to that of alkanes. Because the molecules are arranged in a U-bending configuration, cis-isomer molecules have a lower melting point than trans-isomers.

Polarity

Alkenes, like alkanes, are weakly polar, but due to the presence of double bonds, they are significantly more reactive.

Because the electrons that make up double bonds are weakly bound, they can be easily removed or added. As a result, alkenes have higher dipole moments than alkanes.

The polarity of compounds is determined by the functional groups connected to them as well as the chemical structures.

Chemical properties of Alkene

Alkenes are made up of a lot of weakly held pi bonds. They display addition reactions due to the presence of such bonds. Electrophiles (electron seeking species) are added to the double-bonded molecules in this reaction, resulting in the production of a new product. It also has the ability to undertake free radical substitution reactions under certain conditions. Ozonolysis and oxidation reactions are also vividly displayed.

Dihydrogen addition

When one molecule of dihydrogen is added to alkenes in the presence of various catalysts such as palladium, nickel, or platinum, alkanes are produced.

Addition of halogens

When alkenes react with halogens like bromine or chlorine, vicinal dihalides are generated. Iodine is an exception, as it does not undergo addition under typical circumstances. The addition of bromine to an unsaturated site causes bromine solution to lose its reddish-orange colour in carbon tetrachloride solution. As a result, this reaction is employed to check for unsaturation in a solution. The electrophilic addition reaction is exemplified by the reaction of alkenes with halogens.

Hydrogen halide addition

When hydrogen halides react with it, alkyl halides are produced. HI has higher reactivity than HBr, whereas HBr has higher reactivity than HCl. Both symmetrical and unsymmetrical alkenes can undergo the addition reaction. The addition of hydrogen halides to unsymmetrical alkenes occurs according to the Markovnikov rule and Anti-Markovnikov rule.

When an unsymmetrical alkene is introduced to hydrogen halide, the halogen attaches to the carbon with the least number of hydrogens, according to the Markovnikov rule.

Alkenes and Their Applications

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 fibre

• 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 fibres

Conclusion

It can be considered that Alkenes are important for the chemical industry due to their properties. Alkanes are solely responsible for the formation of Alkene through cracking. As fuel is degrading day by day and the consumption of fuel is much higher, thus Alkene is useful in manufacturing many chemicals that can be used as fuels.