Alkenes Properties

What is Alkene?

In inorganic chemistry, alkene is a compound, which belongs to the family of hydrocarbons. Additionally, it has a carbon-carbon double bond (C=C). Besides alkenes are also regarded as unsaturated hydrocarbons, because they have less than the maximum number of hydrogen atoms per carbon atoms.

Furthermore, the general formula of alkene is CnH2n. Moreover, alkene creates a homologous series comprising molecules that can increase their weight by adding methylene. Probably, the simplest compound in this alkene series is ethane or ethylene (C2H4). Other molecules of this series are propane (C3H6), butene (C4H8), etc. 

Physical Properties of Alkene

The physical properties of alkene are as followed –

1. State Of The Compound: Alkene compounds are naturally odourless and colourless. However, ethane is an exception. Even though it is a gas without colour, it holds a slightly sweet smell. Additionally, the first three compounds of this family of alkene are gaseous, but the next fourteen are liquid, and the remaining ones are solid. 

2. Solubility: Moreover, owing to their nonpolar characteristics, alkenes do not dissolve in water. Contrarily, they are entirely soluble in nonpolar solvents such as ligroin, benzene, etc.

3. Boiling Point: The boiling point of alkene is directly proportionate with its carbon atoms; if it increases, then the boiling point also rises. Additionally, when alkene and alkane’s boiling points are compared, it is found that they are almost similar. Moreover,they have a similar carbon structure. Besides, the boiling point of a straight-chain alkene is higher than the branched-chained ones.

4. Melting Point: The melting point of alkene depends on the positioning of its molecules. Moreover, the melting of this compound is similar to alkanes. On the other hand, cis-isomer molecules have an inferior melting point compared to trans-isomers, as they are packed in a U-bending shape.

5. Polarity: Furthermore, compared to alkanes, alkenes are weakly polar. However, alkenes are marginally more reactive owing to the existence of double bonds. On the other hand, you can easily remove the double bonds or add more, as they are not strongly held. Therefore, the dipole moment exists more in alkenes rather than in alkenes. Nevertheless, this polarity depends on the functional group attached to its chemical structure.

Chemical Properties of Alkene

As mentioned earlier alkene is an unsaturated compound which makes it a highly reactive substance. Moreover, these chemical reactions occur surrounding its carbon-carbon bond. Hence, it becomes more reactive than alkanes. To better understand the chemical properties of alkenes, read the following reactions. 

Reactions of Alkene

The chemical properties of alkenes class 11 make it a relatively stable compound. Here are some of the prominent reactions that alkene takes part.

1. Addition Reactions

In this type of reactions, two or more molecules join together to create a larger one. The end product of these reactions is called an additive product. Furthermore, a number of such reactions follow the mechanism of electrophilic addition. Some of the prominent examples of such reactions are –

• Hydrogenation: This reaction requires a temperature of 200 degree Celsius and the presence of a metallic catalyst. In case of industrial requirements, catalysts based on palladium, nickel, or platinum are used. Moreover, for laboratory synthesis, Raney nickel is used. One of the most common examples of this reaction is catalytic hydrogenation of ethylene to produce ethane. The equation of this reaction is, CH2=CH2 + H2 → CH3–CH3.

• Hydration: With the help of this process, water is added across double bonds of alkenes. As a result, it produces alcohol. Moreover, this reaction is catalysed by either sulphuric or phosphoric acid. Additionally, hydration is used in industries to produce synthetic ethanol. The equation here is, CH2=CH2 + H2O → CH3–CH2OH. Furthermore, Mukaiyama hydration, oxymercuration–demercuration reaction, or hydroboration–oxidation reaction is used to produce alcohol from alkenes. 

• Halogenation: In this process, elemental chlorine or bromine is added to alkenes to produce vicinal dibromo. Moreover, the decolouration of bromine solution in water is a test to identify the presence of alkene. The equation of this reaction is, CH2=CH2 + Br2 → BrCH2–CH2Br. Additionally, related reactions like iodine number of bromine number are used as quantitative procedures of unsaturation. 

• Hydrohalogenation: This process helps in making haloalkanes by adding hydrogen halides like HI, HCI to alkenes. The equation here is CH3–CH=CH2 + HI → CH3–CHI−CH2–H. Moreover, in case the two carbon atoms in double bond are linked to different numbers of hydrogen atoms; thus, halogen is preferably located in carbon with fewer hydrogen substituents.

Furthermore, this process is regarded as Markovnikov’s rule. However, the use of radical initiators or any other compound can result in contrasting results. For instance, hydrobromic acid, in particular, is susceptible to producing radicals due to the presence of impurities or even atmospheric oxygen. Moreover, it moves against the principles of Markovnikov results. This hydrobromic acid reaction is, CH3–CH=CH2 + HBr → CH3–CHH–CH2–Br.

2. Elimination reaction

A popular alkene synthesis is by elimination reaction. This process helps gathering alkene from alcohol, alkyl halide, and others. Moreover, alcohol and alkyl halide goes through dehydrohalogenation dehydration for this purpose. 

3. Oxidation

Oxidation of alkene is possible in many ways with assistance from various oxidising agents.

• Moreover, in the existence of oxygen, alkene burns with a bright flame and creates water and carbon dioxide. 

• Furthermore, reaction with percarboxylix acid or catalytic oxidation process yields epoxides.

• Additionally, reaction with hot and concentrated KMnO4 in an acidic solution will create carboxylic acid or ketones. 

• Lastly, ozonolysis in the presence of ozone helps in breaking the double bond, creating ketones and aldehydes. 

The following reaction aids in determining the position of a double bond of an unknown alkene.

• R1–CH=CH–R2 + O3 → R1–CHO + R2–CHO + H2O

4. Photooxygenation

Photosensitisers like methylene blue and light can help alkene to go through a reaction with reactive oxygen that generates photosensitiser. Some of the prominent examples of such oxygen are superoxide ion, singlet oxygen, and hydroxyl radicals.

Moreover, these photochemical intermediates are created in different types, such as Type I, Type II, and Type III, respectively. Furthermore, these reactions and processes can be controlled by opting for particular conditions. It aids in manufacturing various products. A popular example here is, [4+2]-cycloaddition of singlet oxygen along with diene like cyclopentadiene produces endoperoxide.

Application of Alkene

Alkene has an array of applications in industries. Typically, they are used as starting materials to synthesise alcohols, lacquers, detergent, plastics, etc. Following are some important industrial applications of an alkene.

Ethene is a vital organic feedstock in chemical industries. It is produced from crude oil and natural gas with the help of cracking. Moreover, ethene is used for the production of various chemical products like vinyl chloride, polyethylene, ethanol, styrene, acetaldehyde and several others. 

Another product of alkene, propane, is largely used for the production of polypropylene. Additionally, various oxidation products like acrylic acid, butanol, acrylic acid ester, acrolein, glycerol, epichlorohydrin, and allyl chloride are also produced via this method.

Furthermore, butadiene, other products of alkene is primarily used for producing synthetic rubber.

Alkenes and Olefins

Even though alkenes and olefins are often used interchangeably, it is not accurate. According to IUPAC (International Union of Pure and Applied Chemistry), alkenes include every aliphatic hydrocarbon having one double bond. On the other hand, olefins have a bigger set of compounds, which includes alkenes.

Furthermore, olefins include aliphatic hydrocarbons, be it acyclic or cyclic. Moreover, they can have one or more carbon to carbon double bonds. Examples like alkene, polyenes, cycloalkens compounds exhibit more than one double bond. 

However, if alkene comprises more than one double bond, then this nomenclature alters to alkadiene, alatriene, and so on. Additionally, alkadienes which are often found in fire debris, show that they are pyrolysis products of certain polymers.

Physical properties of alkene is an important chapter of chemistry. Moreover, it is an easy scoring one as well. Thus, students looking for assistance regarding this chapter can visit the official website or download our Vedantu app.

Furthermore, they can access live classes from subject experts and clear their doubts. Moreover, they can avail study material regarding physical properties of alkanes class 11 via this app with ease.