Draw enol tautomer(s) for each compound.

Name: Problem 32, Chapter 23: Organic Chemistry
Uploaded: 2019-06-10T17:14:54-08:00
Duration: 4 min 51 s
Channel: Nima Gharibi
Description: Draw enol tautomer(s) for each compound.

Key Concepts

Tautomerism

Tautomerism is the phenomenon where compounds exist in dynamic equilibrium between two or more structurally distinct forms that differ primarily in the location of a hydrogen atom and a double bond. This interconversion is typically rapid and reversible, impacting the chemical reactivity and properties of the molecules.

Keto-enol Tautomerism

Keto-enol tautomerism is a specific type of tautomerism where a carbonyl compound (keto form) is in equilibrium with its enol form, which contains an alkene and an alcohol group. The positions of a double bond and a proton change during the interconversion, affecting the stability and reactivity of the species.

Enol Form

The enol form of a molecule is characterized by the presence of an alkene (carbon-carbon double bond) adjacent to a hydroxyl group (–OH). Although the enol form is often less thermodynamically favored compared to the keto form, factors like conjugation and intramolecular hydrogen bonding can significantly stabilize it.

Resonance and Conjugation

Resonance stabilization, often enhanced by conjugation, plays a key role in stabilizing the enol form. Through the delocalization of electrons, the molecule can distribute positive and negative charges over a larger framework, which can shift the equilibrium toward the enol tautomer under certain conditions.

Proton Transfer Mechanism

The formation of enol tautomers involves a proton transfer, typically in a catalyzed process by either acids or bases. This hydrogen migration from the alpha carbon to the oxygen atom in the carbonyl group is a fundamental mechanism that enables the interconversion between the keto and enol forms.

Transcript

0:00 Hello everyone.

00:01 Today we're doing chapter 23 problem 32 and this problem asks us to draw the enototomer for each compound so what you see here is that we have a bunch of keto totomers and if i just draw this out we have one two three four five so one two three four five and then this one will look something like this so you see we have a bunch of keto totomers and we need to form the eno forms of these totomers.

00:40 So so how can we go about doing this? well, we see that, for example, in a, we have two alpha carbons, one on either side or one adjacent to either side of our carbonyl group.

00:55 So we have two alpha carbons and we can deprotonate either one.

00:59 So for example, if i deprotonate the left one, then i can get a bond being formed here and then this bond, the carbonyl bond will go to the oxygen nucleus which you can pick up this proton, the alpha proton, to form our enototomer, which looks something like this.

01:24 But at the same time, this oxygen can pick up this proton on the right to form the enel on the right side of the molecule.

01:44 I have a tri -substituted enol here.

01:48 And in terms of stability, well, this enol on the left is going to be more stable because, yes, both of them have only three substitutes on it but now this enol is now in conjugation with this benzene rings so that means that instead of having three levels of conjugation here you're adding extra carbon here so you now have seven carbons or actually eight carbons in conjugation to each other unlike this one is only six carbons in conjugation with these two separate here now we have all these eight carbons now in conjugation with each other so that increases stability of this molecule or of this enol form i should say.

02:25 Now let's move on to b.

02:26 So b we see that on the right side we have no alpha protons but on left we do have alpha protons so we can deprotonate that or oxygen using as lone pair electrons can pick up that alpha proton making a bond you make a bond you make a bond you break a bond so then you form the new alkene bond when you make a bond you break a bond so then you're to break the carbonyl bond to go up to oxygen nucleus to neutralize everything.

02:49 So now you form this enol form here...

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