sulfenic acids

https://doi.org/10.1351/goldbook.S06096
Compounds having the structure $\ce{RSOH}$ ($\ce{R} \neq \ce{H}$), e.g. $\ce{PhSOH}$ benzenesulfenic acid.
Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1368 [Terms] [Paper]