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Hello everybody,

I am currently studying E1 and E2 eliminations and I am trying to understand how to compare the rates at which they proceed for different chemical compounds. Although I know some basic rules still I'm a bit confused when I apply them in practice. I know that E1 is a unimolecular process and once the leaving group is lost, elimination occurs very rapidly. While in E2 elimination the rate depends on the concentration of both the nucleophile and the substrate with the leaving group.

I am given these 4 compounds:
a) R,R-1,2-diphenyl-1-bromobutane
b) R,S-1,2-diphenyl-1-bromobutane
c) R,R-2-bromo-3-chlorobutane
d) R,S-1-bromo-1,2-diiodopropane

and have to find out which will give the  fastest E1/ E2 eliminations.

Please can any of you suggest me anything what to do.  Thank you.

[tamim83]

Hi,

The fourth compound should give the slowest E1 elimination.  That is because the product will be unfavorable because it will be sterically hindered (with the two methyls cis to each other)

The first compound will form an E2 cis alkene the fastest while the second compound will form the E2 trans alkene the fastest.  The reason is that in each case the molecules stereo chemistry allows for each product to form faster.  

I hope this helps.  If you are still struggling, try to use models.  I use them a lot because I have a vision disability.  It really helps when you have to consider stereo chemistry.  

Happy Studying