[BradytoBranch]

Hi guys, I have a quick question about an Organic 2 mechanism problem. I am required to find the step-by-step mechanism for this reaction:

I am a little bit stumped into how to approach this. I am assuming I break the double bond with the oxygen first, which would give me a O- and add double bond somewhere. The main concern is how the cyclopentane changed into a cyclohexane and how to draw that out.

I would appreciate any help. Thank you!

[fledarmus]

This reaction is running in acid, so you won't be forming O^-. Can you give a more likely first step?

[BradytoBranch]

H+ would be seeking an electrophilic center, so I would break a C=C double bond?

[discodermolide]

H+ would be seeking an electrophilic center, so I would break a C=C double bond?

Try protonating the oxygen atom and move some bonds around and see what you can come up with.

[orgopete]

Hint, protonate the carbonyl group and draw all of the resonance structures you can for starters.

[BradytoBranch]

Hint, protonate the carbonyl group and draw all of the resonance structures you can for starters.

Try protonating the oxygen atom and move some bonds around and see what you can come up with.

Ahh I'm a tad confused.
I protonated the oxygen atom and I found the different resonance structures but I still ended up doing nothing to change the lower cyclopentane to a cyclohexane. 

Do you guys recommend a section/site/topic that I can mabye read up on since I obviously am missing out on an important concept?

(BTW: I really really appreciate you guys helping me, I'm loving this forum and you guys)

[orgopete]

Ahh I'm a tad confused.
I protonated the oxygen atom and I found the different resonance structures but I still ended up doing nothing to change the lower cyclopentane to a cyclohexane.

Hint #2, did one of your resonance structures have a carbocation next to a quaternary carbon? (A quaternary carbon can form a tertiary carbocation upon migration.)

Although WE may know the chemistry, we don't know how much help is needed for a poster. If you just wanted the answers, read a book. If a solution is too distant from a problem, then we can try to fill in the gap. The real gap we try to fill in the one that allows posters to solve their own problems.

[discodermolide]

Hint, protonate the carbonyl group and draw all of the resonance structures you can for starters.

Try protonating the oxygen atom and move some bonds around and see what you can come up with.

Ahh I'm a tad confused.
I protonated the oxygen atom and I found the different resonance structures but I still ended up doing nothing to change the lower cyclopentane to a cyclohexane. 

Do you guys recommend a section/site/topic that I can mabye read up on since I obviously am missing out on an important concept?

(BTW: I really really appreciate you guys helping me, I'm loving this forum and you guys)

So you managed to obtain all the resonance structures, good. This infers that you don't need to read about this topic.
Can you break and move one of the cyclopentane bonds in these structures?

[BradytoBranch]

Hint #2, did one of your resonance structures have a carbocation next to a quaternary carbon? (A quaternary carbon can form a tertiary carbocation upon migration.)

So you managed to obtain all the resonance structures, good. This infers that you don't need to read about this topic.
Can you break and move one of the cyclopentane bonds in these structures?

Hmm, I think this is where I have that disconnect. As of now, my mechanism looks like this:
I understand the next important part would be turning that cyclopentane into a cyclohexane, but I am not sure where to go from here. Which bonds would be moving and why/how?

[discodermolide]

Hint #2, did one of your resonance structures have a carbocation next to a quaternary carbon? (A quaternary carbon can form a tertiary carbocation upon migration.)

So you managed to obtain all the resonance structures, good. This infers that you don't need to read about this topic.
Can you break and move one of the cyclopentane bonds in these structures?

Hmm, I think this is where I have that disconnect. As of now, my mechanism looks like this:
I understand the next important part would be turning that cyclopentane into a cyclohexane, but I am not sure where to go from here. Which bonds would be moving and why/how?

You are on the right track.
Move the right hand cyclopentane bond (attached to the 6-membered ring) to the C+ centre, and make a quaternary carbonium ion and 2 fused 6 membered rings.

[BradytoBranch]

EDIT: Whoops nevermind, I see where I missed up, still working on it.

EDIT 2: Ohhh nevermind, I think I'm slowly getting it haha

[discodermolide]

EDIT: Whoops nevermind, I see where I missed up, still working on it.

OK

[BradytoBranch]

OK, for some reason I was absolutely confusing myself into oblivion because I was mainly focused on the "cyclopentane" turning into a "cyclohexane" but I totally miscounted the carbons and incorrectly assumed the entire structure would gain 1 more carbon, whoops!
I documented that right here:


So basically all I have to do now is add the H+/H20 reaction, which would form a double bound where the tertiary carbocation is and I should be all set?

[discodermolide]

OK, for some reason I was absolutely confusing myself into oblivion because I was mainly focused on the "cyclopentane" turning into a "cyclohexane" but I totally miscounted the carbons and incorrectly assumed the entire structure would gain 1 more carbon, whoops!
I documented that right here:


So basically all I have to do now is add the H+/H20 reaction, which would form a double bound where the tertiary carbocation is and I should be all set?

Well done you got it, great

[BradytoBranch]

You are absolutely amazing, thank you and everybody who posted in this thread for all the help. I really cannot thank you enough, I only wish you had used your real name so I can spread the word about you guys. If you are ever in Boston, MA I owe you a drink. Cheers and thank you for the patience.