Concept 6 Review: The Hydroxyl and Carbonyl Groups
Two functional groups containing oxygen, the hydroxyl and carbonyl groups, contribute to water solubility.
Oxygen occurs in these two common functional groups:
• Hydroxyl groups have one hydrogen paired with one oxygen atom (symbolized as -OH). Hydroxyl groups are not highly reactive, but they readily form hydrogen bonds and contribute to making molecules soluble in water. Alcohols and sugars are "loaded" with hydroxyl groups.
• Carbonyl groups have one oxygen atom double-bonded to a carbon atom (symbolized as C=O). Like hydroxyl groups, carbonyl groups contribute to making molecules water-soluble. All sugar molecules have one carbonyl group, in addition to hydroxyl groups on the other carbon atoms.
Carbonyl groups exist in two forms:
• Aldehyde groups, where the C=O group is at the end of an organic molecule. A hydrogen atom is also located on the same carbon atom.
• Keto groups, where the C=O group is located within an organic molecule. All sugars have either a keto or an aldehyde group.