Draw resonance structures of the intermediate carbocations in the bromination of naphthalene, an

step 1 Okay, so we have naphthalene, which is two fused benzene rings. And the question says that it fa

Draw resonance structures of the intermediate carbocations...

Key Concepts

Electrophilic Aromatic Substitution (EAS)

EAS is a fundamental reaction mechanism in aromatic chemistry where an electrophile attacks an aromatic ring to form a non-aromatic carbocation intermediate (arenium ion) before deprotonation restores aromaticity. This process is critical in understanding how and why substitutions occur in aromatic systems.

Resonance Stabilization

Resonance stabilization refers to the delocalization of electrons (or positive charge in the case of carbocations) across multiple atoms within a molecule. For aromatic carbocations, drawing multiple resonance structures illustrates how the positive charge is spread over the ring, thereby enhancing the stability of the intermediate during the reaction process.

Carbocation Intermediates in Aromatic Systems

Carbocation intermediates, also known as arenium ions, are transient species formed during electrophilic aromatic substitution. These intermediates lose aromaticity temporarily but gain stabilization through resonance. Their formation and stability are key factors determining the feasibility and pathway of the substitution reaction.

Regioselectivity in Aromatic Substitution

Regioselectivity in aromatic substitution refers to the preferential site of electrophilic attack on an aromatic compound. In systems such as naphthalene, different positions on the ring lead to intermediates with varying degrees of resonance stabilization, which explains why substitution at one position (e.g., C1) is favored over another (e.g., C2).

Transcript

00:01 Okay, so we have naphthalene, which is two fused benzene rings.

00:06 And the question says that it favors bromination at the one position, which is ortho to where the other benzene ring is fused to.

00:17 And we have to draw resident structures for why it is favored at the first carbon and not the second.

00:25 So what i had done was i already drew all the frameworks, and i'm just going to draw in the pie bonds based on where i'm going to move.

00:31 The charge just to save some time here.

00:35 Right.

00:35 So i think in terms of all of the possible resident structures, we're looking for some factor that's stabilizing our carbon one addition product.

00:47 Right.

00:47 So i think the first thing is that we still have a fully formed aromatic ring.

00:54 Right.

00:54 So i can do the classic benzene arrow pushing here to arrive at this structure.

01:02 So that gives me two resident structures that maintain aromaticity in one of the rings.

01:07 And then i will use the other double bond to move that charge around.

01:15 So now, wait, no, hold the phone, right? i could do the same thing again.

01:19 So boom, boom.

01:22 So now i have four intermediates that allow me to put the charge, that allow me to maintain aromaticity.

01:36 Did you draw that right, right? so now i'm going to take...

01:39 There we go.

01:40 I knew i was forgetting something.

01:42 So now i'm going to take one of the bonds from the other ring and i'm going to force it.

01:46 I'll move the charge into that second ring.

01:50 So now we have a double...

01:51 I hate when i do that.

01:52 I like drawing my bonds inside the rings here.

01:56 So now we have something like that.

01:57 We've broken aromaticity in both rings now.

02:01 So i can just keep moving.

02:03 That charge around.

02:12 And i actually didn't draw one framework.

02:14 I forgot to put it onto that tertiary position.

02:17 So i'm going to put this up here.

02:27 Right.

02:27 So boom, boom.

02:31 And then you have one there, one here, charge there.

02:37 Right.

02:38 And then if i put this bond up here, i arrive back at this structure, right there.

02:45 So we have one, two, three, four, five, six, seven structures, resident structures total, four of which have a full aromatic ring, which contributes to the lowering and energy of the carboccalion as a whole.

03:03 Right.

03:04 So let's see how the meta structure compares...

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