Sn2?

[Dencology]

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i keep getting mixed up. i know that Sn2 produce a optically active molecule which means if we start with R when end up with S at the end through Sn2. but in Sn1 we get optically inactivce molecule because we get a recemis mixture.

Guys if a molecule is chiral and it goes through nucleophilic addition Sn2 will this produce a inversion of the molecule or not? what if the molecule is achiral?

 

[klutzy1987]

i keep getting mixed up. i know that Sn2 produce a optically active molecule which means if we start with R when end up with S at the end through Sn2. but in Sn1 we get optically inactivce molecule because we get a recemis mixture.

Guys if a molecule is chiral and it goes through nucleophilic addition Sn2 will this produce a inversion of the molecule or not? what if the molecule is achiral?

If the molecule starts out as Chiral then there will be a 100% inversion. If it starts as achiral then there will be a racemic mixture.

For SN1 there is a partial inversion so if it started out as R it will end up as 60% S and 40% R.

 

[eldirty]

If the molecule starts out as Chiral then there will be a 100% inversion. If it starts as achiral then there will be a racemic mixture.

For SN1 there is a partial inversion so if it started out as R it will end up as 60% S and 40% R.

This is because SN1 reactions produce a carbocation intermediate as the leaving group leaves allowing the nucleophile to front or backside attack ... therefore a racemic mix. In SN2 reactions a high energy transition state is observed as only a backside attack is produced and therefore inversion of stereo chemistry.

 

[supraman]

The carbocation intermediate in Sn1 will be trigonal planar, so the nucleophile will attack from the top or bottom if you picture the trigonal planar horizontally