ISSUE:

Write the structures of the alcohol and the aldehyde or ketone needed to obtain these compounds:

Hello Jonyv.
It is a good practice to first describe the functional group or groups that the molecule that one wishes to prepare or synthesize has. Thus, in your case, an OH linked to the same carbon atom that contains an OR group (alkoxide) is called a hemiacetal, which is formed from the reaction of an alcohol with a carbonyl aldehyde or ketone compound in a slightly acidic medium.

So, in the case of your hemiacetlaes, they are formed from the substrates indicated in the following scheme:




Greetings.