Electrophilic Substitution Reaction

Electrophilic Substitution Reaction
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1. ELECTROPHILIC SUBSTITUTION REACTION An electrophilic substitution reaction is a chemical reaction in which the functional group attached to a compound is replaced by an electrophile.

2. TYPES OF ELECTROPHILIC SUBSTITUTION REACTION There are two types of electrophilic substitution reaction: SE1 ( Electrophilic substitution unimolecular reaction) SE2 (Electrophilic substitution bimolecular reaction)

3. SE1 (Electrophilic Substitution Unimolecular Reaction) The substitution electrophilic unimolecular mechanism are termed SE1 reactions. These mechanisms follow first order of reaction kinetics with respect to the substrate. The SE1 mechanism involves two steps: The first step is a rate slow determining ionization step leading to formation of the carbanion. The second step involves fast combination of electrophile resulting in to the products.

4. SE1 (Electrophilic Substitution Unimolecular Reaction) STEP1: STEP2:

5. SE1 (Electrophilic Substitution Unimolecular Reaction) Stereochemistry of SE1 mechanism: The chlorination of acetone to α -chloroacetone. STEP1: (c arbanion) STEP2: (α- chloroacetone)

6. The electrophilic substitution bimolecular mechanism are termed SE2 mechanisms. These reactions follow bimolecular rate kinetics, where the reaction rate is first order in substrate and first order in the electrophile when both reactions are in dilute solutions. Stereochemistry of SE2 mechanism: The SE2 reaction mechanism proceeds via a single transition state where the old bonds and the newly bonds are both present simultaneously. There are two possible ways to electrophile attack to the reaction centre. SE2(ELECTROPHILIC SUBSTITUTION BIMOLECULAR REACTION)

7. SE2(ELECTROPHILIC SUBSTITUTION BIMOLECULAR REACTION) a. The first one is attack from the front, which is called SE2 (front) that results in retention of configuration. b. The second option is attack of the electrophile from the rear, which is called SE2(back) that leads to inversion of configuration.

8. DIFFERENCE BETWEEN SE1 & SE2 REACTION SE1 REACTION The electrophilic substitution uimolecular mechanism are represented by SE1. SE1 reaction follows first order kinetics with respect to the substrate. The SE1 mechanism involves two steps: the first step is a slow rate determining ionization step leading to formation of the carbanion. The second step involves fast combination of electrophile resulting in to products. SE2 REACTION The electrophilic substitution bimolecular mechanism are represented by SE2. SE2 reaction follows first order in substrate and first order in the electrophile. The SE2 reaction mechanism proceeds via a single step where the old bonds and the newly formed bonds are both present simultaneously.

9. DIFFERENCE BETWEEN SE1 & SE2 REACTION SE1 REACTION 4. There are only way to electrophile attack to the reaction centre. SE2 REACTION 4. There are only two ways to electrophile attack to the reaction centre: The first one is attack from the front, which is called SE2(front) that results in retention of configuration. The second option is attack of the electrophile from the rear, which is called SE2(back) that results in inversion of configuration.

10. SEi (ELECTROPHILIC SUBSTITUTION INTERNAL REACTION) When the electrophile attacks from the front and a portion of it assists in the removal of the leaving group by forming a bond with the leaving group at the same time when the new bond is formed, the mechanism is called SEi (electrophilic substitution internal reaction). Mechanism of SEi: In SEi mechanism, the electrophiles with suitably placed functional groups attacks the sp3 hybridized substrate from the front, whereby a portion of the electrophile might assist in the removal of the leaving group. It is a concerted mechanism leading to retention of configuration. (retention of configuration)