# Move a pi bond into a cycloalkane

1. Jun 21, 2008

### Phil Massie

Hello. This is driving me a little mad, and some assistance would be hugely appreciated.

1. The problem statement, all variables and given/known data
Show how the following transformation can be achieved (more than one step may be involved)

2. Relevant equations

3. The attempt at a solution
The only approach i could come up with was the following:

1. hydrohalogenation of the alkene substituent with H-Cl, putting a Cl on the more substituted C atom and an H on the less substituted C.

2. dehydrohalogenation should then produce constitutional isomers, as there are 3 $$\beta$$ carbons, 2 of which produce the same molecule (i think) and both constitutional isomers have tri substituted double bonds. the required pruduct is then one of the constitutional isomers, methylcyclohexene.

I just saw in another textbook something about endocyclic $$\pi$$ bonds being more stable than exocyclic $$\pi$$ bonds. Is this the case in this problem? and would that mean that the required product would be the only one formed?

Thanks in advance for any help. Its late and i cant think anymore...

2. Jun 22, 2008

### Spirochete

You're correct there are 3 beta hydrogens, with the possibility of two different products from an E2 reaction. I'm not sure about different stabilities of endo/exo cyclic rings, but even if the two products were equally stable and the two reaction pathways had the same activation energy, you would still get 66% the product you were looking for, because there are twice as many ways to form the product you want.

3. Jun 22, 2008

### Phil Massie

Thanks thanks thanks!
really appreciate you taking the time for this :)
I love these forums!

4. Jun 23, 2008

### chemisttree

You wouldn't even need to hydrohalogenate/dehydrohalogenate. Look at the mechanism of the acid-catalyzed E2 elimination, first step. The product is a carbocation at the 3o carbon. Loss of H+ will give you the endocyclic isomer. Any exocyclic product would be recycled again and eventually the thermodynamic product is obtained.

5. Jul 6, 2008

### Gannon

Using what little I know from basic organic chemistry, I would simply 1) brominate and 2) run an E2 reaction using a sterically-encumbered base such as tert-butoxide.