[beapkman]

Which mercapto group is more nucleophillic?

And i want you guys to answer the reason..

Thank you.

[sjb]

How would you measure nucleophilicity?

[Vrig]

The nucleophilicity would depend on the electrophile aswell. You have hard/soft Nu^- vs hard/soft E⁺, they interact differently with different compounds.

[Babcock_Hall]

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.

[orgopete]

Which is more nucleophilic, CH3NH2 or PhNH2? Wouldn't the same electronic effect apply to a sulfur atom?

[Vrig]

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 2p_z (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

[ashmus]

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.