Reactions of Alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond in their structure. This double bond results in unique reaction properties.
The double bond in alkenes is an area of high electron density. Consequently, it’s susceptible to attack by electrophiles, initiating a range of addition reactions.
Electrophilic Addition: This is the most common type of reaction carried out by alkenes. The addition of a hydrogen halide (like hydrogen bromide) to an alkene forms a halogenoalkane.
Addition of Hydrogen: Alkenes can react with hydrogen in the presence of a catalyst such as finely divided nickel. This is an example of a reduction reaction.
Hallmark test for Alkenes: One key characteristic of alkenes is their ability to undergo addition reactions with bromine water, turning it from orange to colourless. This reaction can be used as a test for the presence of an alkene.
Addition Polymerisation: Alkenes can join together in a reaction to form polymers. This is how plastics such as poly(ethene) and poly(propene) are made.
Markovnikov’s Rule: When an unsymmetrical alkene reacts with a molecule such as a hydrogen halide, there are often two possible products. Markovnikov’s rule helps predict the major product.
Anti-Markovnikov reactions can also occur, however this typically involves more complex, radical mechanisms.
Mechanisms of Reaction: It’s essential to understand the mechanisms involved in these reactions, including the forming and breaking of bonds during the reaction.
Stereoisomerism: Due to the restricted rotation around the double bond, alkenes exhibit a type of stereoisomerism called E-Z isomerism. Knowing how to determine whether isomers are E or Z is crucial.
Synthesis of Alkenes: Alkenes can be produced by the dehydration of alcohols or the dehydrohalogenation of alkyl halides. The exact techniques should be understood for the creation of each specific alkene.
Environmental Impact: Understanding the environmental implications of using and creating alkenes, especially in relation to plastic pollution and sustainable chemistry practises, is also important.

By mastering these topics, a better understanding of alkenes and their reactions can be achieved, which forms a fundamental part of organic chemistry.