Destroyer Ochem #103

[silveryhair]

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Can someone explain what makes the fastest E2 reaction in a cyclohexane?

I read the answers in the back and it got more confusing >.<

 

[Baylor2011]

A strong base in an aprotic solvent, with the best leaving group (I-) being on a tertiary carbon

 

[JeweLie]

A strong base in an aprotic solvent, with the best leaving group (I-) being on a tertiary carbon

I thought that the leaving group being on the tertiary carbon wasn't favored for E2 but E1 instead?

I think that the reaction will occur the fastest for this conformation compared to the other answer choices is because when you put the bulkiest group t-butyl in equatorial position, the leaving group I would in axial position and ready to be eliminated since it's in anti-periplanar orientation.

If you look at all the other answer choices, in A, if you made the t-butyl equatorial, the I would be equatorial too and would have to go thru ring flip in order to get into axial position. Ring flip would also have to occur in C. For D once I is in axial position, it has 1,3 diaxial strain with the t-butyl which causes steric hindrance.

Thus B would be the fastest because it didnt have to go thru a ring flip and it was already in the right orientation for the reaction to occur.
I hope my explanation made sense ^^;;