Hydroxy aldehydes

Glycolaldehyde is the organic compound with the formula . It is the smallest possible molecule that contains both an aldehyde group () and a hydroxyl group (). It is a highly reactive molecule that occurs both in the biosphere and in the interstellar medium. It is normally supplied as a white solid. Although it conforms to the general formula for carbohydrates, , it is not generally considered to be a saccharide.

In organic chemistry, 3-hydroxybutanal (acetaldol, aldol) is an organic compound with the formula and the structure . It is classified as an aldol () and the word "aldol" can refer specifically to 3-hydroxybutanal. It is formally the product of the dimerization of acetaldehyde (). A thick colorless or pale-yellow liquid, it is a versatile and valuable intermediate with diverse impacts. The compound is chiral although this aspect is not often exploited.

Lactaldehyde is an intermediate in the methylglyoxal metabolic pathway. Methylglyoxal is converted to D-lactaldehyde by glycerol dehydrogenase (gldA). Lactaldehyde is then oxidized to lactic acid by aldehyde dehydrogenase.

γ-Hydroxybutyraldehyde is the organic compound with the formula HOCH2CH2CH2CHO. It is a colorless liquid. The compound occurs in nature and is produced commercially.