A selenonic acid is an organoselenium compound containing the −SeO3H functional group. The formula of selenonic acids is R−Se(=O)2−OH, where R is organyl group. Selenonic acids are the selenium analogs of sulfonic acids. [1] Examples of the acid are rare. Benzeneselenonic acid PhSeO3H (where Ph stands for phenyl) is a white solid. It can be prepared by the oxidation of benzeneselenol. [2]