destroyer ochem #70

[silveryhair]

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Why does adding Excess D20, DCl (catalytic) in this compound only replace the CH3?

 

[Charmm]

this is a ketone; aldehydes and ketones do not undergo nucleophylic acyl substitution. The result of addition of H2O/H+ to ketones is a hydrate. In this case you have D2O which means on the hydrate the OD group will be present.

So, the product is Ph-C(OD)2-CH3

 

[Dor17]

^ but the answer was not that.

it was just H's in methyl carbon being replaced with D's

 

[silveryhair]

Yeah, so does anyone know why the hydrogen's are replaced by deuterium's?

 

[newmexomfs]

its actually similar to alpha halogenation of aldehydes and ketone via acid catalyzed mechanism. The reaction ocurs via enolat enolate ion formation. In McmMurry's the reagents are X2(halogens) + Acetic acid. If you use X2 with a Base like NaOH, it is going to lead to Haloform reaction and the products wud be Ph-COO- and CHX3.

 

[mustardseed5]

Yeah, so does anyone know why the hydrogen's are replaced by deuterium's?

it's just heavy hydrogen; hydrogen with a neutron

 

[silveryhair]

Yeah, I know its a hydrogen isotope. I just don't see the mechanism of how the Hydrogens are replaced with the D since its not base catalyzed why would it remove the alpha hydrogens?

 

[Charmm]

I think iremember this question, from the answers you can tell that the writer is after substitution reactions of alpha carbon. A couple of points, first of all in the real test the questions are very straight forward. Secondly, I think the author wants to empphasiE the. Difference between acid catalyzed and base catalyzzed substitutions of alpha carbon. My dat had a claisen but not something like this question. They. Like name reactions of alpha carbon. The answer I. Gavve above is a competing product with the correct answer. Too much details, not a standard question.

 

[Charmm]

Yeah, I know its a hydrogen isotope. I just don't see the mechanism of how the Hydrogens are replaced with the D since its not base catalyzed why would it remove the alpha hydrogens?

First the oxygen of carbonyl is deuterated. Then a D2O molecule abstracts a hydrogen of methyl forming an enol making a double bond and neutralizing the plus charge on oxygen of carbonyl. Then a lone pair of OD makes a pi bond and the pi bond of enol abstracts a D. From a D3O molecule. I hope it makes sense, if not, pm me and I will send a pdf of the mechanism

 

[MowgliR]

First the oxygen of carbonyl is deuterated. Then a D2O molecule abstracts a hydrogen of methyl forming an enol making a double bond and neutralizing the plus charge on oxygen of carbonyl. Then a lone pair of OD makes a pi bond and the pi bond of enol abstracts a D. From a D3O molecule. I hope it makes sense, if not, pm me and I will send a pdf of the mechanism

Can you please post it on here? It'd be super helpful for everyone.


Thanks!

 

[orgohacks]

Can you please post it on here? It'd be super helpful for everyone.


Thanks!

I wrote a post about it a little while back:

http://masterorganicchemistry.wordpress.com/2010/05/05/another-awesome-example-of-acid-catalysis/

Hope this is helpful - James