Now that you have been introduced to the terminology and fundamental ideas of reaction mechanisms, it is time to focus on the reactions of alkenes.
Alkenes react by electrophilic addition which means that the first step in the mechanism is the addition of an electrophile to the C=C double bond. The double bond consists of a sigma bond and a weaker pi bond – the electrons from the pi bond can be deployed in an attack on an electrophile and be used to make a new covalent bond (sigma).
There reactivity of an alkene depends on its stability …
Let’s look at the reaction mechanism for electrophilic addition, starting with the reaction between propene and HBr.
Markownikov’s rule states that on the addition of HX (electrophile) to an alkene, the hydrogen bonds to the carbon atom with the fewest alkyl groups and the X bonds to the carbon with the most alkyl groups.
In the example above, this means we would always make 2-bromopropane, never 1-bromopropane.
The bad news is that you need to learn the reaction conditions for all these organic reactions, but the good news is you have the perfect excuse to make lots of flashcards 😆.