Question

What does the epoxidation of trans-2-pentene produce?

Answer 1

The epoxidation of trans-pent-2-ene produces a racemic mixture of trans-pent-2-ene epoxide isomers.

The mechanism if the reaction is given here.

The addition is a concerted syn addition.

Groups that were cis in the original alkene remain cis in the product. Groups that were trans remain trans.

Compare the epoxidation of trans-but-2-ene.

If we replace a methyl group with ethyl, we see that the epoxidation of trans-pent-2-ene produces trans-pent-2-ene epoxide.

The product is chiral, so we get a 50:50 mixture of the two enantiomers.

The IUPAC name is (`2S`,`3S`)-3-ethyl-3-methyl-2,3-epoxypentane We also get the (`2R`,`3R`) enantiomer.

Heterocyclic compounds are often named by the Hantzsch-Widman system:

• The oxygen atom is indicated by the prefix -oxa. It is automatically atom 1 in the ring, and the "a" is omitted before a vowel.
• The three-membered ring is indicated by the infix -ir (think tri).
• The saturated ring is indicated by the suffix -ane.

So a third name for this compound is (`2S`,`3S`)-2-ethyl-3-methyloxirane.The lower number is assigned to the substituent that comes first in the name. We also get the `2R`,`3R` enantiomer.