Dehydration Problem: Solving for the Location of a Double Bond in a Carbocation

[vijayramakrishnan]

Homework Statement

Please see question number 31

http://cms.fiitjee.co/Resources/DownloadCentre/Document_Pdf_183.pdf

Homework Equations

none

The Attempt at a Solution

i got up to second step in the solution(scroll downwards) but in the last step a carbocation is formed and double bond can be formed in two places b and a. they seem to be equivalent places,i don't know where the double bond will be formed.

 

[TeethWhitener]

Look up Zaitsev's rule.

 

[vijayramakrishnan]

Look up Zaitsev's rule.

but here both are equally substituted sir

 

[TeethWhitener]

Ah, I see now. You're wondering why the double bond doesn't form between the two bridgehead carbons? This might be because you're envisioning protonating the OH group at the bridgehead carbon and eliminating a water to give a tertiary carbocation. In this case however, you have to do something a little different. Start by drawing the molecule in the enol form. Can you get it from here?