[shafaifer]

In this exercise I have to list compounds in order of highest reactivity to lowest reactivity in E₂ reactions. The following compounds (attached) and my thinking are given:

3 > 1 > 2

I think compound 3 is at least more reactive than 1 because number 3 will produce the E-isomer which is more stable than the Z-isomer that will be synthesized with number 1 in an E₂ anti elimination. Also, only anti elimination will occur for all three compounds because the β carbons considered to give rise to the most stable alkenes (according to Zaitsev's rule) in E₂ are only bonded to one hydrogen. I am not really sure how to rank compound 2 but despite the fact that the affect of steric hindrance in E₂ is little I think it still determines the ranking - but I might not be correct and that is why I am searching for help here

[Dan]

I think compound 3 is at least more reactive than 1 because number 3 will produce the E-isomer which is more stable than the Z-isomer that will be synthesized with number 1 in an E₂ anti elimination.

Can you draw the isomers you are talking about? Can you explain why you think 1 will give Z and 3 will give [/i]E[/i]?

Also, only anti elimination will occur for all three compounds

This is the key point of the question. Draw mechanisms for each E2 reaction in 3D - draw each compound in the conformation required to allow E2 (what are the stereochemical requirements for E2?). Now consider the relative stabilities of these compounds in their reactive conformations.

[shafaifer]

Thank you for this point of view, Dan