Which functional group would you expect to be involved in hydrogen bonding with water?

The aldehyde functional group features a carbonyl (C=O) group, which is polar due to the difference in electronegativity between the carbon and oxygen atoms. This polarity allows aldehydes to form hydrogen bonds with water molecules. In hydrogen bonding, the partially positive hydrogen atoms from water can interact with the partially negative oxygen atom of the carbonyl group, resulting in a stable interaction.

In contrast, alkanes and alkyl groups are composed primarily of carbon and hydrogen, which do not have significant electronegativity differences. Therefore, they are non-polar and do not readily engage in hydrogen bonding with water. Thiols, while they possess a sulfur atom that can form weak hydrogen bonds due to the presence of the –SH group, they do not form hydrogen bonds as robustly as the carbonyl in aldehydes does. Thus, aldehydes are the most favorable group for hydrogen bonding with water among the given choices.