Acetic acid fits the general formula C₂(H₂O)₂ but is not a carbohydrate because carbohydrates are defined as optically active polyhydroxy aldehydes or ketones, and acetic acid lacks these specific functional groups.

The general formula for carbohydrates is Cₓ(H₂O)ᵧ. The term “carbohydrate” originates from the idea that these compounds are hydrates of carbon, as seen in the molecular formula of glucose (C₆H₁₂O₆).