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Near-infrared spectra of methanol-acetone and ethanol-acetone mixtures in the entire mole fraction range in increments of 0.1 were recorded in the region of 7500–6000 cm−1. The first overtone bands of the hydroxyl (OH) groups were assigned to the polymeric and oligomeric OH associations. In both solutions, the frequency of the polymeric OH band decreased with the increase in the mole fraction of alcohol, which indicated the increase in the hydrogen bonding strength. The integrated area of the polymeric OH band followed the opposite trend to the frequency with the mole fraction. The nonlinearity of the plot of the integrated band area of the polymeric OH band of methanol versus the mole fraction of acetone revealed the nonideal character of the methanol-acetone mixtures, whereas the opposite was observed for the ethanol-acetone mixtures. These observations have been explained in terms of mechanical and electrical anharmonicities of the OH oscillator. [ABSTRACT FROM PUBLISHER]