A student had prepared three ethyl-substituted...

Name: Problem 54, Chapter 16: Organic Chemistry
Uploaded: 2021-05-16T00:21:38-08:00
Duration: 4 min 23 s
Channel: Temi Ajayi
Description: A student had prepared three ethyl-substituted benzaldehydes, but had neglected to label them. The premed student at the next bench said that they could be identified by brominating a sample of each and determining how many bromo-substituted products were formed. Is the premed student's advice sound?

A student had prepared three ethyl-substituted benzaldehydes, but had neglected to label them. The premed student at the next bench said that they could be identified by brominating a sample of each and determining how many bromo-substituted products were formed. Is the premed student's advice sound?

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Key Concepts

Electrophilic Aromatic Substitution (EAS)

This reaction type is characterized by the attack of an electrophile on an aromatic ring, leading to substitution of a hydrogen atom. The process is influenced by the electronic properties of substituents already present on the ring, which can activate or deactivate the benzene ring towards further substitution.

Substituent Directing Effects

Substituents on an aromatic ring affect both the rate and the orientation of electrophilic substitution. Activating groups generally direct incoming electrophiles to the ortho and para positions, while deactivating groups often favor substitution at the meta position. When multiple substituents are present, their combined directing effects dictate regioselectivity by either reinforcing or competing with each other.

Regioselectivity in Disubstituted Aromatics

In molecules with two substituents, the resulting orientation of new substituents is determined by the interplay of their directing effects. The relative positions of the substituents, steric hindrance, and the electronic influence of each group collaboratively determine the number and identity of possible substitution products.

Transcript

00:01 Here we're looking at benzaldehydes that have a methyl substituents as well.

00:07 Okay, so it could be at the orthoposition, the meta position, or the para position.

00:15 Okay, so with that, if we were to brominate, we actually have two directors going on here.

00:22 Okay, so i'll use green to signify the benzaldehyde or the aldehyde direct.

00:32 And i'll use blue to signify the methyl direction.

00:38 Okay? let's start off with blue.

00:40 So the methyl will direct ortho, para, while the benzaldehyde will also direct the meta position in there.

00:51 Here we have ayesha -not meta.

00:54 It sets ortho, the meta, meta to the aldehyde.

00:59 Okay, so what we actually get for this ortho compound is two double -ed.

01:05 Doubly activated sites.

01:09 Okay.

01:10 And so we have aldehydes and alkyl groups are sort of pretty even in their reactivities.

01:21 The alchal group being more on the activating side, but weak.

01:28 Well, the benzaltahide is a moderately weak the activating group.

01:32 Okay, so we can't really use that to distinguish.

01:36 Okay.

01:36 We see here that we will actually get two bromination products...

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