When organic molecules are synthesized (even if it is 10 steps long), they are formed by these basic reactions. Once you understand the basic idea behind these reaction, it becomes easy to write the synthesis on your own.
In this post, I hope to give you a basic idea about the different types of organic reactions.
Addition Reactions
As the name suggests, this reaction involves the addition of a new group to a compound. Addition of the group is only possible after a double or triple bond breaks. So, the unsaturated compounds undergo this type of reaction.
A compound containing double bond is called an alkene. Each double bond consists of a π bond and a σ bond, π bond is much weaker than a σ bond so requires less energy to break.
A compound containing triple bond is called an alkyne. Each triple bond contains two π bonds and one σ bond. As there are two π bonds, two steps are possible. This leads to the formation of two adducts.
Benzene does not undergo addition reaction under normal conditions as it would lead to the destabilization of the electron system.
Substitution Reactions
When a group gets replaced by another, it is called a substitution reaction. These reactions, unlike addition do not require the presence of an unsaturated compound. Here, a new group is added by replacing the old one. The compound which undergoes this reaction is called a substrate and the group that gets removed is called the leaving group. The intermediate is dependent on the group that’s getting added.
Elimination Reactions
These reactions are the opposite of addition reactions. In addition reaction, an unsaturated compound gives rise to a saturated one whereas, in elimination reactions the end product is an unsaturated compound. So these reactions are used for the synthesis of alkenes and alkynes.
A group or atom is eliminated from the alpha carbon (carbon with a substituent) and a proton is eliminated from the beta carbon (the carbon beside the alpha carbon). The elimination reaction generally takes place when there is a proton attached to the beta carbon.
Rearrangement Reactions
A group gets migrated in these reactions. Here, an atom or group of atoms can migrate within a molecule or from one molecule to another.
Most common rearrangements involve 1,2 shift.
Common migrating groups: carbon, hydrogen, halogen, oxygen, nitrogen.
So, all the reactions you come across in organic chemistry will fall under one of the above mentioned types of reaction. I realised that the moment, I understood the basic mechanism and the reaction itself understanding and learning the synthesis becomes all the more simple. I plan to give detailed explanation on the individual types of reaction (with its classification) along with examples so it becomes easier for you to understand.
