best nucleophile destroyer

[JDHK]

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Which is the best nucleophile?
H20
alcl3
c2h5oh
ch3sh
ch3cooh

I thought it would be water, because although it sucks i THINK its better than the other oxygen derivatives. The answer says it's CH3SH because of its smaller size and less electronegativity. I'm really confused though, Chad said in his video that in aprotic solvents, which im assuming CH3SH is, results in the trend that u get better nucleophiles as you go up the column, so isn't O better than S?. What am i missing here?

 

[denttal]

When you are comparing the nucleophilicity of non-charged molecules, as you go down a group, you increase nucleophile strength. So electrons on a "S" will be better at attacking an electrophile than electrons on an "O". This is because the electrons on the S are farther away from the nucleus and they can attack better, if you will. I think it has something to do with in the transition state (having better overlap of orbitals) it is stronger when the electrons are farther from the nucleus.

I think the answer says that CH3SH is the strongest b/c of it's "smaller size" in that it is not bulky so it will be easier to attack an electrophile. Also, EN does decrease as you go down the periodic table. So electrons on the Sulfur atom are being pulled on less than the electrons on an Oxygen atom would be.

 

[denttal]

Also, there is no solvent specified so you are simply looking at the nucleophiles that are listed in the question.