The pK,'s of o-nitrobenzeneselenenic acid (la) and three 4-substituted-2- nitrobenzeneselenenic acids (lb-d) have been determined at 25" C in water. A Hammett plot of the pK,'s gives ap value for the ionization of ArSeOH (eq 3) of+ 1.4. The pK, of la is 10.45, which makes it 2.8 times weaker as an acid than phenol. Areneselenenic acids are therefore surprisingly weak acids. If the only influence of the o-nitro group on the acidity of la is its ...
