Quiz - Electrophilic Aromatic Substitution - 2 | Electrophilic Aromatic Substitution
Organic Chemistry 2 - Quiz - Electrophilic Aromatic Substitution - 2
Which of the following mechanistic steps is common to all electrophilic aromatic substitution (EAS) reactions?
The common mechanistic step in all EAS reactions is the generation of a resonance-stabilized carbocation, known as the sigma complex.
During the halogenation of benzene, which catalyst is typically required to generate the electrophile?
A Lewis acid such as FeCl3 or AlCl3 is required to generate the electrophile in the halogenation of benzene by making the halogen molecule more electrophilic. This facilitates the formation of the halonium ion, which is the active electrophile in the reaction.
In Friedel-Crafts alkylation of benzene, which of the following statements is true about the electrophile formation?
In Friedel-Crafts alkylation, the electrophile is a carbocation that is formed from an alkyl chloride and a Lewis acid catalyst such as AlCl3. This step is key in forming the potent electrophile that will react with the benzene ring.
Which of the following conditions favor Friedel-Crafts acylation over alkylation when reacting with benzene?
Friedel-Crafts acylation involves the use of an acyl chloride and a Lewis acid catalyst. Acylation is often preferred over alkylation as it avoids problems like carbocation rearrangement and over-alkylation, leading to more controlled synthesis.
How does the presence of a strong electron-withdrawing group attached to the benzene ring affect electrophilic aromatic substitution?
A strong electron-withdrawing group decreases the electron density of the benzene ring, making it less nucleophilic and thereby destabilizing the sigma complex. This results in a decreased reaction rate for EAS processes.
In the presence of an activating group and a deactivating group on a disubstituted benzene, which group predominantly influences the outcome of an EAS reaction?
The activating group, due to its resonance effect, usually exerts a stronger influence on the outcome of an EAS reaction on a disubstituted benzene. It increases electron density and directs electrophiles to ortho and para positions.
What is the primary reason for the regioselectivity observed in the nitration of disubstituted benzene compounds?
The electronic effects of the substituents, whether they are activating or deactivating, have a primary effect on the regioselectivity of EAS reactions. These effects determine the relative reactivity of the ortho, meta, and para positions.
Why is sulfonyl protecting group preferred in multi-step syntheses involving nitration of benzene?
A sulfonyl protecting group is preferred because it can be easily introduced and removed, allowing specific functional groups to be protected while other reactions on the benzene ring take place. This selectivity is key in complex syntheses.
For a successful Friedel-Crafts alkylation, which of the following is essential to avoid polyalkylation?
To avoid polyalkylation in a Friedel-Crafts alkylation, it is important to use an equivalent ratio of benzene to alkyl halide. This minimizes the chance of multiple alkyl groups attaching to the benzene ring.