[hybrid]

Hello,

The reaction I wanted to ask about uses PCC & celite in order to oxidize the carbons shown in circle (in the GIF file). What is the mechanism of this oxidation? also, what is the origin of the carbonyl oxygen? (I don't see any reliable source of oxygen...)

Thank you

[movies]

PCC does all kinds of crazy oxidations if you let it.  This is actually one of the more common ones.  The mechanism probably occurs through a radical intermediate, although it's a little hard to say for sure.  The benzyllic position is oxidized preferentially because the radical intermediate can be be stabilized by the adjacent aromatic system.  The oxygen can only come from one place: the PCC!

[Organishe]

I can see how the benzylic oxidation would occur, but how does the oxidation from the alkane to the alcohol happen?

Again, I would assume a radical mechanism, and I'm also assuming it would occur after the benzylic oxidation. I assume that because then you can do some kind of oxidation alpha to the carbonyl (giving more options for radical/charge stabilization)

Another side question, why wouldn't the other benzylic carbon be oxidized to an alcohol (I can see why it doesn't go to a ketone, for the obvious reason). A radical at that position would be highly stabilized, seeing as its such an electron rich ring.

[AWK]

Oxidation usually have radical mechanism, except some very specific oxidation reagents. Benzylic and tertiary carbon atoms a te the most susceptible to oxidations. Strong oxidation agents oxidise a secondary alcohols to ketones, and eventually benzylic methyl groups to carboxylic ones.

[movies]

Organishe, I agree with your assessment that the alpha position gets oxidized after the ketone is formed.  As for why the other benzyllic position doesn't get oxidized, your guess is as good as mine.  Here is my guess:

There is little possibility for orbital overlap between the aromatic ring and the other benzyllic C-H bond because to do so you would induce a lot of strain by putting the isopropyl group in the same plane as the aromatic ring.  I suppose that the isopropyl group sits with the C-H bond in the plane of the aromatic because it is the smallest group and that minimizes strain with the methyl groups.  The consequence is that even if you did form a radical at that benzyllic position, it would not be stabilized by the adjacent aromatic ring.