SN2 inversion of configuration

[westphi]

If the Sn2 rxn results in inversion of configuation...then shouldn't a molecule go from one absolute configuration to the other? i.e. go from R to S or S to R.

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[sicboy188]

If the Sn2 rxn results in inversion of configuation...then shouldn't a molecule go from one absolute configuration to the other? i.e. go from R to S or S to R.

not always the case. It really depends on how the addition of the attacking nucliophile and loss of the leaving group changes the priorities around the chiral center. Ur interpretation of Sn2 isnt hard and fast.

 

[The South Face]

Only if the nucleophile has the same priority as the leaving group.

 

[tncekm]

There is an inversion of relative configuration.

So, when you draw out the inverted SN2 product do so with the group that has left so you know the relative inversion configuration--then replace the group that has left with the nucleophile and then determine its absolute configuration. This may or may not be the same relative configuration!

 

[westphi]

Thanks everyone. I guess I failed to recognize that the nucleophile could be a different priority than the leaving group. Cheers!

 

[tncekm]

Sounds like you've got a great handle on it, now.