[AL258]

I don't quite understand how this mechanism works, so if someone could point me in the right direction...

What I know is that H2SO4 at 100°C causes dehydration, so I'm not quite sure why there is a ring reduction and a ketone group formed.

As far as the mechanism goes, I think it's something like this:

1. One of the Oxygen gets protonated
2. Leaving group of H2O causes a cation to form

Then I'm not sure what happens next, or if I was even going in the right direction.

[Dan]

You are on the right track, once the carbocation forms, a cationic migraton occurs.

http://en.wikipedia.org/wiki/Pinacol_rearrangement

[AL258]

Oh, I see how the ketone forms now. But what would cause the ring reduction?

[Dan]

The ring contraction? Try drawing the mechanism of the pinacol rarrangement, which group is migrating in this case?

[AL258]

The methyl group migrates, right? Causing the cation to be with the -OH group. Then electrons from the Oxygen creates a double bond, moving the cation to the oxygen, but then the hydrogen goes to the HSO4-, leaving its electron behind, making the oxygen neutral again...

Edit:
Wait... I think I see what happens. The 2nd carbon in the cyclic compound is migrating, right?

Edit 2:

Nevermind, that is still wrong.

[Dan]

Correct. You should make sure you know why a ring contraction occurs rather than methyl migration.

Hint: Look up "migratory aptitude"

[AL258]

Is this the correct mechanism?

[Dan]

Yes.

Just make sure you know why the major product is not 2,2-dimethylcyclohexanone.

[AL258]

Awesome, thank you so much, Dan!