Reactivity towards Elimination Reaction

Elimination reaction is a type of organic reaction in which a molecule loses a small molecule, usually a proton (H+) and a leaving group, resulting in the formation of a double or triple bond. The reactivity towards elimination reactions depends on several factors, including the nature of the substrate, the strength of the base, and the reaction conditions.

Factors Affecting Reactivity Towards Elimination Reaction

1. Substrate
The reactivity towards elimination reactions is influenced by the nature of the substrate. The key factors include:
- The type of carbon atom: The reactivity typically follows the order of tertiary > secondary > primary carbon atoms. This is because the stability of the carbocation intermediate formed during the reaction increases with increasing substitution.
- Presence of electron-withdrawing groups: Substrates with electron-withdrawing groups, such as halogens or carbonyl groups, enhance the reactivity towards elimination reactions. This is due to the increased stability of the resulting double or triple bond.

2. Base Strength
The strength of the base used in the elimination reaction plays a crucial role in determining the reactivity. Strong bases, such as hydroxide ion (OH-) and alkoxide ion (RO-), are highly reactive and can effectively remove a proton, leading to a faster elimination reaction. Weaker bases, such as water or alcohol, are less reactive and may require harsher reaction conditions or longer reaction times.

3. Reaction Conditions
The reaction conditions, including temperature and solvent, can significantly influence the reactivity towards elimination reactions. Higher temperatures generally increase the reaction rate by providing more kinetic energy to the reacting molecules. The choice of solvent can also affect the reactivity, as polar solvents tend to favor elimination reactions by solvating the reactants and facilitating their interaction.

Order of Reactivity Towards Elimination Reaction

1. Tertiary Substrates
Tertiary substrates have three alkyl groups attached to the carbon atom undergoing elimination. They are the most reactive towards elimination reactions due to the increased stability of the carbocation intermediate. The presence of electron-withdrawing groups further enhances their reactivity.

2. Secondary Substrates
Secondary substrates have two alkyl groups attached to the carbon atom undergoing elimination. They are less reactive compared to tertiary substrates but more reactive than primary substrates. The stability of the carbocation intermediate is lower than that of tertiary substrates.

3. Primary Substrates
Primary substrates have only one alkyl group attached to the carbon atom undergoing elimination. They are the least reactive towards elimination reactions due to the lower stability of the carbocation intermediate. Primary substrates require stronger bases or harsher reaction conditions to undergo elimination.

It is important to note that this order of reactivity is a general guideline and may vary depending on the specific reaction conditions and substrate. Additionally, the steric hindrance caused by bulky substituents or the presence of other functional groups can also affect the reactivity towards elimination reactions.

2nd order reaction