substitution reaction question

[chiddler]

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It proceeds by SN2 mechanism. I'm thinking of the 5 ligand intermediate. Both Cl and I are bonded with carbon and then the leaving group dissociates.

Haven't we established multiple times in these forums that for a protic solvent, iodine is the best nucleophile and it reverses when the solvent is aprotic? Therefore, with acetone, we should expect chlorine to be the most nucleophilic.

Shouldn't there be no reaction?

or am i mistaken (probably). According to a similar question i just finished, an SN2 reaction occurs.

 

[EnginrTheFuture]

The fact that acetone is your solvent is sounding alarms to me. I would say it's an enol reaction. You can do enol reactions in strong acid solution, you can do them in strong basic solution (I think)... but a weak base?


With that said, acetone is not a protic solvent and I think you are saying it is. Maybe not, but that's the vibe I got.

Hmmmmm.... food for thought

 

[milski]

The I replaces the Cl in the alkane? I am so screwed in ochem. 🙁

And make an enol from what, the acetone? Then you'll end up with something quite different?


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[EnginrTheFuture]

The acetone has a hydrogen on the carbon NEXT to the carbonyl carbon (the beta carbon). This is slightly acetic because when you pluck the h off... the electrons can resonate to the oxygen and make an enol.

The enol form only stays like that briefly but when it reverts back, the electrons come back down and rather then attack an H+ (the reverse of the enol formation), it attacks the reactant as a nucleophile.

This reaction is SLOW and may not be what they are looking for but it is not entirely impossible. What makes this reaction attractive to me is that once it occurs, it is not going to reverse because it forms a C-C bond whereas the other LG switching reaction reaction will go back and forth in an equilibrium fairly regularly.

Orgo is usually my thing and this has me scratching my head.

 

[chiddler]

acetone does not take part in the reaction. there is no acid nor base to catalyze enolization!

 

[chiddler]

apparently this happens...

it's due to solubility of the ions in organic phase. not required knowledge for mcat, but easy to see that it is due to the polarizability of the ions.