[weshawk5]

Organic Chemistry I take home test, we are able to use all resources except other students in class, im stumped so I thought I would ask here.

THe question is as follows...

"The following reaction involves the formation of an alkene from an alcohol; however the product is not exactly what you might expect.  Draw a mechanism and try to explain in your own words what happened in this reaction."

The reaction given is attached as a jpeg file - im at work right now and had to draw it on microsoft paint but its still pretty clear.

My thoughts so far are... that obviously the H2SO4 dehydrates the alcohol, water leaves, and we have a carbocation on that carbon.  I know a 7 membered ring is less stable then a 6 membered ring.  Would the ring simply break and rearange...I know this happens but I cant logically see a reason why it happens in this situation.  Ive considered shifts within the ring but just cant give a logical reason for this happening.

If someone has any tips for me to lead me in the right direction that would be awesome...im sure I can draw the mechanism based on an explination so dont worry about that.

Any help would be greatly appriciated

[NTUstudent]

When shifting there is tertiary carbocation, more stable.
and also there is six membered ring!

[weshawk5]

When shifting there is tertiary carbocation, more stable.
and also there is six membered ring!

Right I understand that...but if one of the methyl groups shifts to the carbon that the hydroxyl group was attached to to produce a tert. carbocation, how does the product look like it does...with both methyl groups attached to the same carbon?

[weshawk5]

Nvm i just got it...thanks!!

[weshawk5]

Wait a second why would the ring close...I'm here but not sure why the ring would actually close.  I wouldn't think c- would attack the other carbon and close the ring?   

[weshawk5]

there should be one more methyl group hanging off of the carbocation in the first pic

[NTUstudent]

after shifting, in the pic you've just drawn carbon(2nd to the right from carbcation) will be bonded with carbon which is positively charged now, and carbon with two methyl groups will be postively charged, then you obtain double bond! sorry i can't draw it.

[cupid.callin]

Tell me if i'm right
I Hope this might help.

[NTUstudent]

Tell me if i'm right
I Hope this might help.

initially the ring is seven membered

[democanarchis]

Wagner-meerwein rearrangement

[cupid.callin]

Oh Yes!!! I'm Sorry, i didnt looked at it carefully...
But democanarchis is totally right.  thats the correct mechanism