Organic Chemistry question

ManBearPig

Diamond Member
Sep 5, 2000
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I have a test in a few days, and I'm having a problem with E2 reactions...which fucking proton is made into a double bond? Of course it has to be adjacent to the removed halogen, but can it be ANY proton that's adjacent? I know what the major product would be, but I dont know which (is it all?) proton it would be. i know there arent rearrangements so it would have to be right next to it.

thanks...this isn't a homework question, it's just been annoying me.
 

MrToilet

Senior member
Feb 28, 2005
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Are you talking about electron movement? Protons don't usually move in E2 rxns, if I remember my organic correctly...

Correct me if I'm wrong, but the alpha-Carbon (attached to the halide) will have a slight "positive" charge from its proximity to the negatively charge halogen, so it tends to be more stable with electrons; the beta-carbon (C next to the one attached to the halide) is the one that donates the electrons.

So: CH3-CH2(X) --> (E2) --> CH2=CH2, with the first carbon donating electrons.

In branched compounds, the one with higher substitutions will generally be more stable in alkenes, so the "least stable" -R group will donate the electrons. (stability: Methyl < secondary < tertiary)
 

Fritzo

Lifer
Jan 3, 2001
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I was going to answer this thread, then realized I misread it. I'm an expert in ORGASMIC chemistry...a completely different field. Sorry.
 

Wisp

Junior Member
Apr 22, 2005
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The eliminating hydrogen needs to be antiperiplanar to the halide, pseudo-halide or whatever.
 

Bill Brasky

Diamond Member
May 18, 2006
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Mr. Toilet is correct on proton movement. Look at the diagram on this page. Link

The curved arrows show electron movement, and I think it's a pretty clear explanation of E2's. Does that link answer your question?
 

ManBearPig

Diamond Member
Sep 5, 2000
9,173
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HAHAHA! a guy named Zaitsev answering this, awesome! So does the proton have to be trans to the halogen that was removed? Sorry...I'm really terrible at organic chem!
 

yhelothar

Lifer
Dec 11, 2002
18,409
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What do you mean by which proton? If I'm reading your question correctly, I don't think atoms bond by individual protons. Rather all the protons of an atom collectively has a charge that attracts the electrons of another atom. When atoms bond, that's when the atoms bonded together are sharing electrons.
 
Dec 10, 2005
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Originally posted by: Kazaam
HAHAHA! a guy named Zaitsev answering this, awesome! So does the proton have to be trans to the halogen that was removed? Sorry...I'm really terrible at organic chem!

Sort of, it just has to be in the same plane as the leaving group.

Like this:
http://en.wikipedia.org/wiki/I...imination_Reaction.png
The methyl group with the heavy line is in the same plane as the the dashed hydrogen on the right carbon. The dashed methyl group is coplanar with the dark hydrogen bond on the right, and the blue hydrogen is in the same plane as the bromine.

The best way to visualize this if your having trouble is to use a molecular model kit. It will make it much easier to see how the bonds can break and form based on spacial orientation.