The values for the sulfur-oxygen stretching frequencies of isomer A of phenylmercuric benzenesulfinate (the O-sulfinate) in chloroform (p 494) are incorrect. It has now been found that isomer A in chloroform reacts with sodium chloride plates, and the reported sulfur-oxygen stretching frequencies correspond closely to those of sodium benzenesulfinate. When silver chloride plates are used, the values for the chloroform solution (1053 and 850 cm-1) are close to those (p 494) for solid isomer A (Nujol mull). This observation invalidates the conclusion (p 494) that isomer A is polymeric or dimeric (structure IV) in the solid state. It now appears probable that this isomer is a monomeric O-sulfinate complex (structure II or III) in the solid state, as in chloroform. It follows that the other RHg(S02R) derivatives (Table I, p 495) with sulfur-oxygen stretching frequencies similar to those of isomer A are likely to have a similar structure.