Propose a mechanism for the electrophilic fluorination of benzene with F-TEDA-BF4.

Name: Problem 2, Chapter 16: Organic Chemistry
Uploaded: 2020-05-12T20:05:42-08:00
Duration: 5 min 18 s
Channel: Matthew Lueckheide
Description: Propose a mechanism for the electrophilic fluorination of benzene with F-TEDA-BF4.

step 1 Okay, so Ah, this is a type of floor nation free agents. We call it Select Floor. That's what's

Propose a mechanism for the electrophilic fluorination of...

Key Concepts

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an aromatic compound, like benzene, reacts with an electrophile. In this process, the aromatic ring temporarily loses its aromaticity upon attack by the electrophile, forming a sigma complex (arenium ion), followed by a deprotonation step that restores the aromatic system. This mechanism is key to understanding how electron-deficient species are introduced onto aromatic rings.

Electrophilic Fluorination

Electrophilic fluorination involves the introduction of a fluorine atom into an organic molecule via an electrophilic species, rather than by a nucleophilic fluorine source. Reagents designed for electrophilic fluorination, such as F?TEDA?BF4, generate a positively polarized fluorine atom that can interact with electron-rich aromatic rings, making it possible to form carbon–fluorine bonds under mild conditions.

Generation of the Electrophilic Species

The mechanism relies on the formation of an active electrophilic fluorinating species from the reagent. This species is sufficiently electron-deficient to attack the aromatic ring. Understanding the nature of this electrophile, including its polarization and leaving group characteristics, is essential in rationalizing the reactivity and selectivity observed in electrophilic fluorination reactions.

Sigma Complex (Arenium Ion) Formation and Re-aromatization

The reaction mechanism includes the formation of a sigma complex, also known as an arenium ion, resulting from the initial attack of the electrophilic fluorine on the aromatic ring. This intermediate, although non-aromatic, is stabilized by resonance. Its subsequent deprotonation is critical as it re-establishes the aromaticity of the ring, finalizing the substitution process. This two-step process, involving the formation and resolution of a sigma complex, is central to understanding the transformation.

Transcript

00:01 Okay, so ah, this is a type of floor nation free agents.

00:05 We call it select floor.

00:07 That's what's over the arrow.

00:08 Um, and it's an electro filic floor nation engine, and the reason why we call it that is because you're you're used to foreign being negatively charged, right, if you're breaking, if you're breaking a flooring, usually it's a hf bonds.

00:23 If you're using hydrofluoric acid, usually the electrons were going toe foreign.

00:26 Um, you're used to foreign being f minus, having eight veiled swatch runs.

00:31 Well, in this case, this may be the first example of, um, flooring actually being electra filic.

00:38 So in this case, you have to think of flooring being, um, only really having, um ah, formal formally, like six valence electrons.

00:48 So it's gonna leave as f plus.

00:51 That's going to get attacked by some nuclear file.

00:53 That's going to give it the extra two electrons that completes vaillant show.

00:57 So if you'll notice in this case, this the base has to nitrogen is that have four bonds? right? so the one on the right i'll draw the green arrow here has four bonds.

01:08 Also carbon, those air pretty relatively inert.

01:12 So, like the nitrogen that i drew my arrow to is gonna be a nri active.

01:16 It's going to stay positive, and one of these before and ions tetro for a boring is what we call that is gonna counter after that charge.

01:25 So what we're gonna do here is you know, you understand that if we have to form this carbon carbon bonds here, we have to break this flooring nitrogen bonds here.

01:34 So just think of this as being, um your electra file cereal tra file is already given to you in the form of this re agent here, um, and push electrons like you would any nitrogen based, um, nitrogen based material.

01:50 Right? so you could start with benzene and, you know, the first step of elektra filic.

01:55 Aromatic substitution is the breaking of room notice ity or the slow step, i should say, is the breaking of roma tissue to form some carbon canada.

02:06 I had the longest part is gonna be me drawing this base here consistently, so i'll take this will impair.

02:13 I think that bond there push them to flooring.

02:15 Electrons go back to nitrogen.

02:17 So now nitrogen is gonna be, um, as you're used to seeing nitrogen witches with three bonds and one lone pair to give you a neutral form of nitrogen.

02:27 I got ahead of myself there.

02:29 Wrestle put foreign on that adam there.

02:32 Which means, um, the formerly sp to hybridize.

02:36 So it what's the last remembrance? but the formerly engaging in ah, double bonds there, you're gonna put flooring on one carbon cap and goes on the other.

02:44 And now you're gonna have your base.

02:45 I'm gonna not, um nothing the whole thing.

02:49 So your next gen is going to, um uh because i will.

02:57 Ah, your nitrogen is going to be neutral now.

03:00 It's now one of your bf fours is going to stay over here.

03:04 Be a four minus just to counteract charge...

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