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Chemistry · Glossary

What is SN2 mechanism, Walden inversion?

Also known as: SN2 mechanism · Walden inversion

Definition 19.2 University Chemistry — Year 1 · Chapter 19 — Nucleophilic Substitution

The SN2 mechanism (substitution, nucleophilic, bimolecular) is a single elementary step in which the nucleophile attacks the carbon from the side opposite the leaving group while the leaving group departs. The three other substituents of the carbon flip over, like an umbrella turned inside out: the Walden inversion.

The SN2 reaction of hydroxide with (S)-2-bromobutane. The nucleophile attacks the face opposite the bromine (curly arrows); in the transition state the O–C bond is forming while the C–Br bond breaks; the product is (R)-butan-2-ol: the three other groups have flipped to the other side.
The SN2 reaction of hydroxide with (S)-2-bromobutane. The nucleophile attacks the face opposite the bromine (curly arrows); in the transition state the O–C bond is forming while the C–Br bond breaks; the product is (R)-butan-2-ol: the three other groups have flipped to the other side.
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