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Topic: [Help] Organic Chemistry  (Read 2579 times)

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Offline 13ored

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[Help] Organic Chemistry
« on: July 11, 2013, 03:35:54 PM »
http://imgur.com/qnwTHfl

Any help in explaining what's going on would be greatly appreciated.

I'm having troubles understanding exactly what I'm supposed to do in these situations. In the top left I'm unfamiliar with BrMgCh_2Ph, so I don't know what the intended effect is.

The top right confuses me. I'm looking at it and struggling to think of exactly where the bonding would take place. Both of the rings are aromatic, and either way both will have their aromaticity temporarily broken so I can't quite figure out where it would occur. I imagined it would be at the joint of the two since those two carbons would be the most suitable carbocations, but that still leaves 2 open.

In the bottom right, I'm unsure of how to use MeLi at all, and my google-fu hasn't aided me in the slightest.
« Last Edit: July 11, 2013, 04:50:45 PM by Arkcon »

Offline gritch

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Re: [Help] Organic Chemistry
« Reply #1 on: July 11, 2013, 09:22:14 PM »
In the top right, BrMgCH2Ph is what is known as a Grignard reagent. Grignards are incredibly basic and are typically used in synthesis as sources of nucleophilic carbons. They are basic enough to react violently with water and unprotected alcohols. A typical electrophile that reacts with a Grignard would be a ketone, which it reacts with to form the corresponding alcohol after acidic work up.

https://en.wikipedia.org/wiki/Grignard_reaction

For the top left. This is a hydroboration reaction if memory serves. I would add to the alkene that's not part of the aromatic ring, even if it is conjugated with the pi-system removing it does not remove the aromatically of the phenyl ring.

http://en.wikipedia.org/wiki/Hydroboration

For the bottom left. MeLi is a organolithium reagent, another organic metallic compound akin to the previously described Grignard. Organolithiums have similar reactivatity to Grignards. In this case methyl lithium is likely being used as a strong base rather than a nucleophile and as such is capable of deprontonating the alkyne hydrogen making the alkyne itself a nucleophile.

I think that's it. Hoped it helped. My organic chemistry's already getting a tad rusty.

Offline rrr

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Re: [Help] Organic Chemistry
« Reply #2 on: July 17, 2013, 07:01:32 PM »
In the top right BH2 must attack the double bond, so that the resulting carbocation would be stabilized by aromatic ring.

Offline rrr

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Re: [Help] Organic Chemistry
« Reply #3 on: July 17, 2013, 07:14:34 PM »
In the bottom right try to look at MeLi as nucleophilic substitution reagent in the first stage.

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