Why Elimination competes over substitution reaction

The competition between elimination and substitution reactions depends on several factors:

1. The nature of the substrate: Primary substrates usually undergo substitution reactions, while secondary and tertiary substrates are more likely to undergo elimination reactions.

2. The strength and bulkiness of the base/nucleophile: Strong, bulky bases favor elimination reactions because they can more easily remove a proton from the substrate, leading to the formation of a double bond. On the other hand, small, less basic nucleophiles favor substitution reactions because they can more easily attack the electrophilic carbon.

3. The solvent: Polar protic solvents favor substitution reactions, while polar aprotic solvents favor elimination reactions. This is because polar protic solvents can stabilize the transition state of the substitution reaction, while polar aprotic solvents can stabilize the transition state of the elimination reaction.

4. The temperature: Higher temperatures favor elimination reactions because they have a higher activation energy and are therefore more sensitive to temperature changes.

In conclusion, whether a reaction undergoes elimination or substitution depends on a combination of these factors.