Give the products, if any, of each of the following...

Key Concepts

Regioselectivity in Aromatic Bromination

Regioselectivity in aromatic bromination revolves around the directing effects of substituents already present on the aromatic ring. Electron-donating groups usually direct electrophilic bromination to the ortho and para positions, whereas electron-withdrawing groups favor meta substitution. In highly activated aromatics, such as those with strong activating substituents, multiple bromination events can occur, often leading to polybrominated products if the reaction conditions are not carefully controlled.

Ring Deactivation in Friedel-Crafts Reactions

Certain substituents, particularly strong electron-withdrawing groups, deactivate an aromatic ring by lowering its overall electron density and reducing its ability to participate in electrophilic substitution reactions. In the context of Friedel-Crafts reactions, such deactivation can prevent the formation of the expected alkylated products even when reactive electrophiles are generated, making these reactions highly dependent on the electronic nature of the substrate.

Lewis Acid Catalysis

Lewis acid catalysis involves catalysts that can accept electron pairs, thereby activating electrophilic species. In reactions like Friedel-Crafts alkylation, Lewis acids such as aluminum chloride interact with alkyl halides to generate more reactive carbocations or electrophilic complexes. This activation enables the aromatic ring to undergo substitution, but the efficacy of the catalyst can vary depending on the substituents present on the aromatic substrate.

Substituent Effects in Aromatic Reactions

Substituent effects refer to the influence that various functional groups exert on the reactivity and regioselectivity of an aromatic ring during electrophilic substitution reactions. Electron-donating groups (EDGs) enhance reactivity and direct new substituents to ortho and para positions, while electron-withdrawing groups (EWGs) decrease reactivity by deactivating the ring and typically direct any substitution to the meta position. Understanding these effects is crucial for predicting the outcome of aromatic reactions.

Electrophilic Aromatic Substitution (EAS)

EAS is a fundamental reaction mechanism in aromatic chemistry where an electrophile replaces one of the hydrogen atoms in an aromatic ring. The process generally involves the formation of a sigma complex (arenium ion intermediate) followed by deprotonation, restoring the aromaticity of the ring. This mechanism underlies many aromatic substitutions and is influenced by the nature of substituents already present on the ring.

Friedel-Crafts Alkylation

Friedel-Crafts alkylation is a subtype of electrophilic aromatic substitution that introduces an alkyl group into an aromatic ring using an alkyl halide and a Lewis acid catalyst. The Lewis acid activates the alkyl halide, generating a carbocation-like electrophile that attacks the aromatic ring. However, this reaction is highly sensitive to the electronic nature of substituents on the ring, and strong deactivators can render the reaction ineffective.

Transcript

00:02 Suppose we want to predict these products.

00:06 Well, let's take the first reaction.

00:08 We have a benzonitral reacting with methyl chloride in the presence of our lewis acid catalyst.

00:14 Well, this reactant should automatically tell us that we are looking at friedelcraft's alkylation.

00:24 So we need to make sure that we have an orthoparadirecting group on our benzene.

00:29 In other words, we need to make sure we have an electron pushing or an activating group.

00:35 And if we look at this one, we have nitral.

00:39 Now, nitral has a triple bond.

00:44 And when it engages in resonance, one of those bonds goes onto the nitrogen.

00:52 And the electrons from the benzene makes a double bond with the carbon.

00:58 This tells us that it's electron withdrawing, not electron pushing, which means that it is a deactivating group.

01:06 And therefore meta -directing, which also means that it will not undergo fidelcraft's alkalation.

01:20 Let's try this example.

01:22 Fenol reacted with bromine.

01:25 Now, right off the bat, it kind of looks like there would not be a reaction because there is no catalyst, right? however, alcohols, and to that extent, ethers are very, very strong electron pushing groups.

01:48 In fact, they would push their electron pairs into the benzene ring really well and would donate those electrons and kind of activate the benzene ring, which makes it an activating group, which makes it orthopara directing.

02:07 And because it's so strong, it doesn't need a catalyst for this reaction to occur.

02:13 And since it's ortho -paradirecting, we'll have our two products...

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