The characteristic vibrational band associated with the C&dblbnd;O group of acetic acid has been studied as a function of concentration of acetic acid in benzene, in carbon tetrachloride, and in isopropyl ether. The effects of benzene and carbon tetrachloride on the band were approximately the same. In both solvents the band became sharper, its intensity was increased, and its center was shifted ... [Show full abstract] to the longer wave-lengths. For concentrations of acetic acid as low as 6 percent the shift amounted to 0.15μ. Although in isopropyl ether solution there was a measurable shift of the band to the longer wave-lengths, the shift was small compared to that observed for benzene and carbon tetrachloride solutions. It is suggested that the changes in the C&dblbnd;O acetic acid band are likely due to variations in the polymerization of the acetic acid as the concentration is varied. However, the position of the band does not approach that for the vapor state in any of these solvents. Ethyl acetate was also studied in benzene and in isopropyl ether; no shifts could be detected in the C&dblbnd;O band.