In contrast to selenonic and seleninic acids, selenenic acids are unstable with respect to a self-condensation reaction to form the corresponding selenoseleninates or disproportionation into corresponding seleninic acids and diselenides:
:2 RSeOH  →  RSe(O)SeR + HO
:2 RSeOH  →  RSeOH  +  1/2 RSeSeR
Even the very bulky 2,4,6-tri-tert-butylbenzeneselenenic acid disproportionates readily. A stable selenenic acid was synthesized by burying the SeOH functional group within the cavity of a [[Calixarene|p-tert-butyl[calix[6]arene macrocycle]]].  X-ray crystallographic analysis revealed the Se-O bond length to be 1.763 Å. The Se-O absorbs in the IR spectrum at 680–700 cm. In a stable selenenic acid prepared by oxidizing a highly hindered selenol, BmtSeH, the Se-O bond length was found to be 1.808 Å while the O-Se-C angle was 96.90°. Oxidation of BmtSeOH gave BmtSeOH.
Selenenic acids are believed to be transient intermediates in a number of redox reactions involving organoselenium compounds.  One notable example is the syn-elimination of selenoxides.  Selenenic acids are also transient intermediates in the reduction of seleninic acids as well as the oxidation of diselenides. The reasoning for postulating selenenic acids as reactive intermediates is based in part on analogy with their more extensively studied sulfenic acid analogs.