Polar Transition State SN2

[SaintJude]

The question was:

In an SN2 rx, are the nucleophile and the transition state polar or nonpolar? A: polar.

How come the transition state is polar? I thought the nucleophile would have a positive partial charge.

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[chiddler]

The question was:

In an SN2 rx, are the nucleophile and the transition state polar or nonpolar? A: polar.

How come the transition state is polar? I thought the nucleophile would have a positive partial charge.

nucleophile and LG are never equivalent, yes? so one must be more polar than the other. since the transition state is not symmetrical, then there must be some dipole moment in some direction.

a nucleophile seeks +, therefore is negative (as an ion, anyway)! so if anything it should be partially negative.

 

[DavetheMD]

The answer is very clear in the transition state of your picture. The leaving group also bears a partial negative at the transition state because it steals the electrons from the bond with the alpha carbon.