C5H9O2

C5H9O2 is the chemical formula consisting of five carbon atoms, nine hydrogen atoms, and two oxygen atoms. In chemistry, a given molecular formula can correspond to multiple structural isomers, so C5H9O2 does not designate a single compound but a family of possible structures. However, for neutral, closed-shell organic molecules composed only of C, H, and O, this particular formula is not feasible: the calculated degree of unsaturation would be 1.5, which cannot occur for a stable neutral molecule. As a result, there are no ordinary neutral compounds with the exact formula C5H9O2.

In practical contexts, the formula is encountered mainly as an ionic or radical form rather than as a stable neutral species. The most common related and chemically well-defined species are the carboxylate anions derived from five-carbon carboxylic acids, such as valerate (pentanoate) and its branched isomeric forms. These anions have the formula C5H9O2− and represent the conjugate bases of C5H10O2 acids (for example, pentanoic acid and its isomers). Thus, C5H9O2− can occur in salts or in biochemical and analytical contexts as a deprotonated carboxylate.

The closest widely recognized neutral formulas with five carbons and two oxygens are C5H10O2, which describe several isomeric acids and esters, including pentanoic (valeric) acid and various branched carboxylic acids. In summary, C5H9O2 is not a standard neutral compound but a formula that is most commonly associated with carboxylate ions or transient fragments in analytical settings.