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Topic: Help Identifying Nucleophile Strength  (Read 30547 times)

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Offline minimal

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Help Identifying Nucleophile Strength
« on: January 13, 2009, 06:32:21 PM »
Hello, I am working on a problem here for fun, the question is.

Rank the following strength of the nucleophiles in diethyl ether.

Group I: H2O HO- H2N- H3N
Group II: CH3Li NaCN CH2=CH2

Ok, for group one, I would say it mirrors strength of the base, because diethyl ether is a aprotic solvent, and thus the nucleophiles are not stabilized by hydrogen bonds.  (I'm not looking up pka values for this).
NH2- is a stronger base than OH-.  Is this because the electron donating effect of the hydrogens?  Also, the O is more electronegative, stablizing it more as an anion.
so so far NH2- > OH -.
The logic would follow for protonated groups, correct?  The same way that HI is a stronger acid than HCl, and I is a weaker base than Cl.
So NH2- > OH- > NH3 > H20

For the second group, I am going to say CH3Li is the strongest nucleophile, due to the unstable nature of the CH3 anion.  Then NaCN, due to the negative charge.  And finally the nucleophilic pi bond of ethene.

Offline Gregorian

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Re: Help Identifying Nucleophile Strength
« Reply #1 on: January 14, 2009, 11:07:26 AM »
Hi,
this link should be helpful

http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch08/ch8-5.html

The nucleophile strength in diethyl ether should be the opposite from what it is in water
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