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Topic: I have quenstions. Which one is more nucleophillic?  (Read 2436 times)

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Offline beapkman

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I have quenstions. Which one is more nucleophillic?
« on: January 21, 2013, 12:30:15 AM »
Which mercapto group is more nucleophillic?

And i want you guys to answer the reason..

Thank you.

Offline sjb

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Re: I have quenstions. Which one is more nucleophillic?
« Reply #1 on: January 21, 2013, 02:12:56 AM »
How would you measure nucleophilicity?

Offline Vrig

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Re: I have quenstions. Which one is more nucleophillic?
« Reply #2 on: January 21, 2013, 07:37:25 AM »
The nucleophilicity would depend on the electrophile aswell. You have hard/soft Nu- vs hard/soft E+, they interact differently with different compounds.

Offline Babcock_Hall

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Re: I have quenstions. Which one is more nucleophillic?
« Reply #3 on: January 21, 2013, 09:16:23 AM »
By the rules of the forum, you are supposed to show an attempt.  Nucleophilicity is dependent on a number of factors, including the identity of the solvent.

Offline orgopete

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Re: I have quenstions. Which one is more nucleophillic?
« Reply #4 on: January 22, 2013, 10:03:51 AM »
Which is more nucleophilic, CH3NH2 or PhNH2? Wouldn't the same electronic effect apply to a sulfur atom?
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Offline Vrig

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Re: I have quenstions. Which one is more nucleophillic?
« Reply #5 on: January 22, 2013, 11:27:18 AM »
I think in that case PhNH2 would be more nucleophilic than CH3NH2, just because of the amount of delocalized electrons. The non-bonding-pair of electrons on CH3NH2 are the only ones who could attack nucleophilicly, while on PhNH2 you have three sites of nucleophilic attacks (ortho/para to -NH2). Might be wrong though...

The reason why is because of electron donation from nitrogen (as it has it's orbital aligned the same as the orbitals which take care of the delocalized electrons), sulfur would have to have sp2 hybridization with lone-pair running parallel to the delocalized orbitals. Also sulfur would have it's valance electrons in the 3s/p shells (or 'd') while nitrogen has its lone-pair in 2pz (if z-direction is in the same direction as carbon orbitals who house the delocalized electrons). This would inevitebly lead to a poor overlap in comparison to nitrogen.

Again, I might be wrong as I'm still learning ;p

Offline ashmus

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Re: I have quenstions. Which one is more nucleophillic?
« Reply #6 on: January 22, 2013, 01:39:59 PM »
Under normal conditions (absence of high heat, pressure, strong Lewis acids), we generally would not consider nucleophilic attack from the aromatic ring. Your rationale about PhNH2 having the ability to delocalize its electrons would therefore make CH3NH2 more nucleophilic (basically electron withdrawing effects from the aromatic ring pulls electron density away from the nitrogen, thus making it less nucleophilic). Although sulfur-carbon has poor orbital overlap, the delocalization of electrons found on the sulfur atom should still occur.

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