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Topic: Mechanism for para-isomer and why methoxy directs ortho/para  (Read 2124 times)

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Offline Joseph216

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Mechanism for para-isomer and why methoxy directs ortho/para
« on: November 01, 2012, 04:26:35 PM »
Hi,

This is part of an exam I got back and am trying to figure out where I lost points. I got half credit for this problem, I'm not quite sure what I left out. I apologize for the messiness of my work, hopefully you can still make out the original problem!!

It is the first problem on the page. I think I can figure out the 2nd problem on the page, but if anyone can answer that problem also it would be greatly appreciated.

Offline BetaAmyloid

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Re: Mechanism for para-isomer and why methoxy directs ortho/para
« Reply #1 on: November 01, 2012, 08:04:44 PM »
This would be my answer...which I'm pretty sure is correct (hopefully one of those smart organic people like Dan or discodermolide checks it):
EDIT: The reaction that is ortho directing, I forgot to show the 3rd carbon of the benzene ring to have a positive charge.
Discovery consists of seeing what everybody has seen and thinking what nobody has thought - Albert Szent-Györgyi

Offline Joseph216

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Re: Mechanism for para-isomer and why methoxy directs ortho/para
« Reply #2 on: November 01, 2012, 09:27:20 PM »
Thank you BetaAmyloid! I'm comparing it to what I had to see where I went wrong / left out. Thank you again!!!

Offline orgopete

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Re: Mechanism for para-isomer and why methoxy directs ortho/para
« Reply #3 on: November 02, 2012, 09:17:13 AM »
It is unfortunate the grade did not include any marks to identify the deductions. Both mechanisms would result in some deductions. I am not sure why the deductions were as large as they were, but the curved arrow should be toward the aluminum, it doesn't have electrons to donate. The resonance arrows are not double headed, and the rearomatization step was missing.

Second problem, you'd have to find my electronegativity arguments that I have posted in the past if you want to know why thiophenol is more acidic. Oxygen is the second most electronegative element, so you cannot use an electronegativity argument. Then you need to apply whatever argument you were given to explain why electronegativity arguments fail. Size or charge distribution are popular arguments.
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