Question

2 molecules of Acetaldehyde can only be made from which of these alkenes?

Answer 1

2 molecules of Acetaldehyde is the product of a reaction of an alkene. One way in which alkenes can react to give carbonyl compounds (ketones/aldehydes) is the reaction with ozone, O₃. The ozonolysis of an alkene will result in cleavage of the carbon-carbon double bond and each carbon that was part of the alkene, will now have a double bond to oxygen. Each carbon of the original alkene will now be a carbonyl in the product.

To form 2 molecules of acetaldehyde, we must cleave an alkene that has the same substitution pattern on each side of the alkene so that the carbonyl compounds formed are identical. Therefore, both (E)- and (Z)-2-butene will react with ozone to give acetaldehyde. The scheme provided shows the reaction of both alkenes to give the acetaldehyde. The products are drawn in such a way to show which part of the original molecules they were derived from. However, both reactions do provide identical products.