HS(=O)OH, sulfinic acid, and its
S-hydrocarbyl derivatives, e.g.
(CH3)2CHS(=O)OH propane-2-sulfinic acid.
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1369 (https://doi.org/10.1351/pac199567081307)