If the ring closure is an #S_N2# reaction then what should be the arrangement of the #-O-C-C-X# system?

1 Answer
Ernest Z.
Jan 9, 2015

The O-C and C-X bonds must be anti to each other.

One way to prepare an epoxide is to react a halohydrin with a base.

www.chem.ucalgary.ca

An example is the conversion of 3-bromo-2,3-dimethylbutan-2-ol to 2,3-epoxy-2,3-dimethylbutane.

wikipremed.com

The reaction is really an intramolecular Williamson ether synthesis.

Step 1 is an acid-base reaction. The OH⁻ removes a proton from the alcohol. This converts it to an alkoxide ion and enhances the nucleophilicity of the oxygen atom.

Step 2 is an intramolecular #"S"_"N"2# substitution displacement of the bromine atom.

#"S"_"N"2# reactions involve "backside" attack on the carbon bearing the leaving group.

The C-O⁻ bond and the C-Br bond must therefore be anti to each other.

Related questions
See all questions in Epoxidation
Impact of this question
3414 views around the world
You can reuse this answer
Creative Commons License