Electrophilic Aromatic Substitution
Electrophilic Aromatic Substitution: Bromination of Aromatic Compounds
Introduction:
The experiment focuses on finding out what kind of activating effects that four different substituents will have on an aromatic benzene ring. The substituents being tested are aniline, anisole, acetamide (acetanilide), and phenol. All four of these groups are either para or ortho activating. Bromination is the reaction that will be carried out. The melting point ranges of the final products will be taken in order to determine their identities and reactivity. It is predicted that substitution order from most to least reactive should be aniline, phenol, anisole, and acetamide.
Theory:
Regioselectivity and the rate of electrophilic aromatic substitution are affected by the substituents attached to the original benzene. In electrophilic aromatic substitution, (EAS for short), the rate determining step is the first step of the reaction. This experiment deals with activating substituents that increase the rate of reaction. In the first rate determining step, the electron density rich pi bonds of benzene react with the electrophile (Bromine) to form a resonance stabilized carbocation. This step is the most important factor that decides which substituents make benzene react faster. This is because the rate of the reaction can be determined through the stability of the carbocation transition state hybrid, which is also known as resonance effect and the Hammond Postulate. In other words, if a carbocation intermediate is more stable, there is less energy needed in the transition state to form the carbocation. Less energy needed translates to a faster reaction. All in all, substituents that increase the electron density on the ring contribute by making the benzene ring more nucleophilic through increased electron density. The increased electron density around the ring would help to stabilize the positively charged carbocation intermediate. This means that this intermediate is more likely
Introduction:
The experiment focuses on finding out what kind of activating effects that four different substituents will have on an aromatic benzene ring. The substituents being tested are aniline, anisole, acetamide (acetanilide), and phenol. All four of these groups are either para or ortho activating. Bromination is the reaction that will be carried out. The melting point ranges of the final products will be taken in order to determine their identities and reactivity. It is predicted that substitution order from most to least reactive should be aniline, phenol, anisole, and acetamide.
Theory:
Regioselectivity and the rate of electrophilic aromatic substitution are affected by the substituents attached to the original benzene. In electrophilic aromatic substitution, (EAS for short), the rate determining step is the first step of the reaction. This experiment deals with activating substituents that increase the rate of reaction. In the first rate determining step, the electron density rich pi bonds of benzene react with the electrophile (Bromine) to form a resonance stabilized carbocation. This step is the most important factor that decides which substituents make benzene react faster. This is because the rate of the reaction can be determined through the stability of the carbocation transition state hybrid, which is also known as resonance effect and the Hammond Postulate. In other words, if a carbocation intermediate is more stable, there is less energy needed in the transition state to form the carbocation. Less energy needed translates to a faster reaction. All in all, substituents that increase the electron density on the ring contribute by making the benzene ring more nucleophilic through increased electron density. The increased electron density around the ring would help to stabilize the positively charged carbocation intermediate. This means that this intermediate is more likely