sulfinic acids

https://doi.org/10.1351/goldbook.S06109
$\ce{HS(=O)OH}$, sulfinic acid, and its S-hydrocarbyl derivatives, e.g. $\ce{(CH3)2CHS(=O)OH}$ 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 [Terms] [Paper]