Physical Properties. Molecules of aldehydes and ketones cannot form hydrogen bonds with each other. Thus, they have lower boiling points than alcohols of similar molecular weight. However, aldehydes and ketones have higher boiling points than alkanes of similar molecular weight because of the presence of the polar carbonyl group. Low molecular weight aldehydes and ketones are soluble in water due to the polarity of the carbonyl group, and the fact that aldehydes and ketones can form hydrogen bonds with water.

Chemical Properties. Aldehydes and ketones are prepared by the oxidation of primary and secondary alcohols, respectively. Aldehydes can be further oxidized to carboxylic acids, but ketones do not undergo further oxidation. Aldehydes are oxidized by Tollens' reagent (Ag⁺) and Benedict's or Fehling's solution (Cu²⁺). Ketones yield a negative result to these tests. Both aldehydes and ketones can be reduced to form primary and secondary alcohols, respectively. In a reaction that is very important in carbohydrates, an alcohol can add across the carbonyl group of an aldehyde to produce a hemiacetal, a primary carbon that is both an ether and an alcohol. The further reaction of a second alcohol molecule with the hemiacetal produces an acetal, a primary diether. Ketones can undergo similar reactions to form hemiketals (a secondary alcohol-ether)and ketals (a secondary diether).

Important Aldehydes and Ketones. Formaldehyde is a gas at room temperature and pressure. It is a key industrial chemical in the production of thermosetting plastics. Formalin is its most common useage when it is dissolved in water and used as a biological preservative. Acetone is an important solvent. Several aldehydes and ketones are used as flavorings (such as vanillin and cinnamaldehyde) in a variety of commercial products.