Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Suzie on December 13, 2006, 01:57:10 PM
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Hi everyone
Could i possible ask for some help on the above?
I have to draw and name the products of the above reaction, giving all the reaction steps! But i am totally lost on this, its the last of a line of questions, and my brain has totally blown.
Its 22 years since i did any chemistry! I am here a bended knees begging, please can anyone help???
Suzie x
p.s. I'm new to the boards, so if i have put this in the wrong place, sorry!
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Hi everyone
Could i possible ask for some help on the above?
I have to draw and name the products of the above reaction, giving all the reaction steps! But i am totally lost on this, its the last of a line of questions, and my brain has totally blown.
Its 22 years since i did any chemistry! I am here a bended knees begging, please can anyone help???
Suzie x
p.s. I'm new to the boards, so if i have put this in the wrong place, sorry!
Alcohol + acid == elimination rxn. I think it's an E1.
First protonation of the hydroxyl group makes it an excellent leaving group. Then it will have a hydride shift to make a tertiary carbocation which is stabalized by hyperconjugation.... hmmm not sure it the ring will break to relieve the ring strain.... But i think you should end up with an alkene if that helps..
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I my opinion ... o.O:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fspiryt.feelfreedom.net%2Fhi.gif&hash=9aea81cba946a6a94e60194e91d0ff68a9f0a327)
greets :)
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That's a special cation called a cyclopropylcarbinyl cation. It can also rapidly rearrange to the cyclobutyl cation.
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Why would Chloride get to attack? I know it is in HCl, but HCl is in water and it is used as a catalyst to generate the hydronium ion which will protonate that OH group, not the HCl, right? because of entropy, there are more water molecules that HCl... im so confused cause that goes against what i learned.. I'm a noob at this btw, so i'm probably wrong.
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I don't think the Chloride ion would attack the carbocation.
I could be wrong, but I believe that reaction will result in the formation of an alkene... most likely 1-methyl-cyclopropene unless the ring breaks like ch3m boy said.
EDIT: I accidentally typed 1-cyclopropene originally (should have been 1-methyl-cyclopropene
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I don't think the Chloride ion would attack the carbocation.
I could be wrong, but I believe that reaction will result in the formation of an alkene... most likely 1-cyclopropene unless the ring breaks like ch3m boy said.
Ya chloride wont get to attack, if it was a substituion rxn, then Water would get to attack and deprotonate again... But this woudl turn an alcohol into an alcohol... Makes no sense..
It has to be an elimination reaction
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For me it is SN1 (substitution, nucleophilic, unimolecular) reaction.... :|
"SN1 reactions can be preparatively useful in organic synthesis, but only in cases where:
Particularly stable carbocations are formed, and elimination reactions are either impossible, or reactions conditions have been adjusted in such a way that elimination reactions are suppressed."
Exemple:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.personal.psu.edu%2Fthe1%2Fsn1e1p3.gif&hash=c1ec1dca35a3af505fe84c3c3fd93c616c956ee0)
So...for me it will be like on my GIF on top of the topic :)
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Here is my proposed mech:
(https://mywebspace.wisc.edu/srlee2/web/1-methyl-cyclopropene.JPG?uniq=c6s5yv)
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I'm curious what Yggdrasil will say because hes smart ;) :)
I agree with steve on his entire mechanism....
Spiryt, i still don't get why Chloride would attack the carbocation. HCl is in water, so if it was an SN1 reaction, water would attack the carbocation (DUE TO ENTROPY) and then it would deprotonate so you have an OH, but that is turning a alcohol into an alcohol.. i dont get it..
Oh ya, and it's not HCl that protonates the OH group..
HCl + H20 --> H3O(+) + Cl(-) hydronium is the acid.
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I'm curious what Yggdrasil will say because hes smart ;) :)
I'm sorry to disappoint, but I don't have too much new insight into the problem other than that I agree with mike:
That's a special cation called a cyclopropylcarbinyl cation. It can also rapidly rearrange to the cyclobutyl cation.
I think the steric strain of a cyclopentane ring is enough of a driving force to get the carbocation to rearrange into a less strained molecule such as a cyclobutylcation. Plus, a cyclopropane ring is strained enough. The cyclopropene ring that UWSteve drew is extremely strained and highly unfavored. There would be a fairly strong driving force for an acid to come along and protonate the alkene, giving you your carbocation again.
Since all these processes are reversible, you don't need to necessarily look at which reactant will react first (i.e. due to entropy). The reactions will be under thermodynamic control; that is, whichever product is most stable will be your major product. Only when your reaction is irreversible should you consider a reaction to be under kinetic control.
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Oops, I screwed up. That's not a cyclopropylcarbinyl cation. You could get to one with a couple of hydride shifts, but that seems kinda unlikely.
If you do get elimination products, you'd probably get the exocyclic olefin, not the endocyclic one because the strain of sp2[/sup] bonds in a 3-membered ring is pretty terrible.
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So if we have methyl group and cyclocompound...there is migration plus load (+) to methyl group? o.O
I must talk to my lecturer and ask him anyway ;)
(Edit: Suzie -> UWSteve is right :) Now I know why and how :) greets and thanks guys :))
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I guess "A" is the major product and "B" is the minor product.
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So if we have methyl group and cyclocompound...there is migration plus load (+) to methyl group? o.O
I must talk to my lecturer and ask him anyway ;)
(Edit: Suzie -> UWSteve is right :) Now I know why and how :) greets and thanks guys :))
Yea, and you can almost be guaranteed, if the compound has the opportunity to shift like that into a 5 or 6 membered ring it'll happen. 5 and 6 membered rings make happy compounds :)
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So if we have methyl group and cyclocompound...there is migration plus load (+) to methyl group? o.O
I must talk to my lecturer and ask him anyway ;)
(Edit: Suzie -> UWSteve is right :) Now I know why and how :) greets and thanks guys :))
Just look up "carbocation stability" in your book, and it should make perfect sense. Just remeber that tertiary > secondary > primary >> methyl :)
Glad I could help in some way, sorry my mechanism was wrong.