Rank the following aromatic compounds in the expected order of their reactivity toward Friedel-C

Rank the following aromatic compounds in the expected order...

Key Concepts

Lewis Acid Catalyst Sensitivity

Lewis acids, such as AlCl3, are essential for generating the electrophile in Friedel-Crafts alkylation; however, they are susceptible to deactivation by strongly coordinating substituents. Functional groups with lone pairs, like -OH and -NH2, can complex with the catalyst, effectively poisoning it and rendering the aromatic substrate unreactive under Friedel-Crafts conditions.

Directing Effects

In electrophilic aromatic substitution reactions, substituents not only alter the overall reactivity of the aromatic ring but also direct incoming electrophiles to specific positions (ortho, meta, or para). Activating groups typically direct electrophiles to the ortho and para positions whereas deactivating groups often lead to substitution at the meta position.

Friedel-Crafts Alkylation

This reaction involves the introduction of an alkyl group onto an aromatic ring through the generation of a carbocation intermediate in the presence of a Lewis acid catalyst. The reaction’s success depends on the ability of the aromatic system to stabilize the positive charge in the transition state, making the electron density of the ring a critical factor.

Substituent Effects on Aromatic Reactivity

Substituents on an aromatic ring influence its reactivity by either donating or withdrawing electron density. Electron-donating groups increase the ring’s electron density, thereby activating it toward electrophilic attack, while electron-withdrawing groups reduce the electron density and deactivate the ring, making it less reactive in electrophilic aromatic substitution reactions.

Transcript

0:00 All right.

00:01 So given these six compounds, we have to rank them in order of reactivity towards friedelcraft's alkylation.

00:07 Which compounds are unreactive? so we're going to start with that second part.

00:11 I want to know which compounds are going to be unreactive before i start ranking them.

00:16 Right.

00:16 So with friedelcraft's alkylation, you're looking for rings that are sufficiently deactivated with strong deactivating groups.

00:24 And the halogens don't count.

00:26 So really anything more deactivating than the halo benzene rings.

00:31 Or the halogenated benzene rings are fair game for not working.

00:36 But also anilin and amino groups are incompatible with the aluminum chloride in the mixture.

00:44 They can be protonated, but the anilinin is also a pretty strong base.

00:50 So it actually coordinates the aluminum and prevents the lewis acid activation by aluminum chloride, being able to form that fourth chlorine aluminum bond is not going to be, it's going to be difficult when you have things like aniline binding to it.

01:06 I've also heard that phenols also give aluminum chloride a problem, but the textbook doesn't say that those reactions don't happen, but phenol might also give aluminum chloride a problem.

01:20 But the textbook says explicitly that deactivated rings and amino groups are incompatible.

01:25 So we're going to follow the direction of mixed mariner.

01:28 So i'm going to go ahead and cross out d &e here.

01:32 So this nitro group is strongly deactivating and you have an amino group on anilin.

01:36 So those are going to be unreactive.

01:38 And then we can just rank the other one...

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