Sn2 Intermediate partial charges?

[homycraz2]

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Lets say you are doing a simple Sn2 and get the following intermediate.



[Nu -----------C(R2)------------Lg ]

Would the Nu, and the Lg both have a partial negative charge? What about the C?

Now if we have H2O acting as the Lg from an alcohol, we know we need to protonate it so that we get R-O^+H2.

How would that effect the partial charges?

[Nu -----------C(R2)------------OH2 ]

 

[Cawolf]

The nucleophile and leaving group will both have partial negative charges due to the partially formed bonds with electrons polarized away from the carbon.

This doesn't change with water, though the oxygen does bear a formal positive charge - this doesn't change the bond polarization in the transition state.

In regards to the partial charge on carbon - I have seen it written both ways (neutral and partial positive). Generally I think the carbon is neutral due to cancellation of the partial positive vectors.