Cl2/H30+ Reaction in orgo DAT Destroyer Road maps

[GDragon_1988]

---

Members don't see this ad.

Does anyone know how this reaction works? I looked in all my notes, and I don't think chad's mentioned this. How does chlorine attach to the alpha carbon position? What would happen if this was in basic conditions?

Thanks!

 

[Cool Beans]

This is alpha halogenation. Under acidic conditions the ketone/aldehyde tautomerizes to an enol. This then acts as the nucleophile attacking Cl2. The result is one of the alpha hydrogens being substituted for by a halogen.

Under basic conditions the alpha carbon is deprotonated forming an enolate. This is a much stronger nucleophile than an enol and also attacks Cl2 also resulting in one of the alpha hydrogens being substituted for by a halogen.

The big difference is that with excess under basic conditions every alpha hydrogen can be substituted for with a halogen. But under acidic conditions it usually only happens once.

 

[GDragon_1988]

This is alpha halogenation. Under acidic conditions the ketone/aldehyde tautomerizes to an enol. This then acts as the nucleophile attacking Cl2. The result is one of the alpha hydrogens being substituted for by a halogen.

Under basic conditions the alpha carbon is deprotonated forming an enolate. This is a much stronger nucleophile than an enol and also attacks Cl2 also resulting in one of the alpha hydrogens being substituted for by a halogen.

The big difference is that with excess under basic conditions every alpha hydrogen can be substituted for with a halogen. But under acidic conditions it usually only happens once.

Thank you so much!!

 

[RedRifle31]

And how can you tell the difference between this rxn and a haloform?


Sent from my iPhone using SDN mobile

 

[GDragon_1988]

And how can you tell the difference between this rxn and a haloform?


Sent from my iPhone using SDN mobile

this video should help

 

[RedRifle31]

So the haloform rxn doesn't allow ALL the alpha carbons to receive halogens? Is that the takeaway?


Sent from my iPhone using SDN mobile

 

[GDragon_1988]

So the haloform rxn doesn't allow ALL the alpha carbons to receive halogens? Is that the takeaway?


Sent from my iPhone using SDN mobile

I don't think so. to my knowledge, it looks like it's still alpha halogenation. But with iodoform, it's in basic solution. the alpha carbon will still bond with halogens; base promotes multiple halogens to be at the alpha carbon. I believe the most ideal alpha carbon for the haloform rxn is the one that can hold 3 halogens since it's considered a good leaving group. For my question, I think i finally understand because mine dealt with a cyclohexanone. a carboxylate ion isn't possible because it's in a ring form and it was in acidic conditions. With open chain, i think you have to approach it differently.
Just my thoughts so correct me if i'm wrong

 

[Cool Beans]

The haloform is unique to methyl ketones. It isn't until 3 hydrogen atoms are replaced by 3 electron-withdrawing halogens that the carbon could be stable enough to exist as an anion and therefore act as a leaving group. If an alpha carbon only has 1 or 2 alpha hydrogens (aka isn't a methyl group) the haloform reaction would not occur.