Effect of Pressure on the Frequency of the O–H Band in Butanol Solutions

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Abstract
The infrared spectra of dilute solutions of normal butanol have been observed in the 3‐micron region at pressures from 10 to 12 000 atmospheres. The sharp ``monomeric'' O–H band shifts toward lower frequencies as the pressure increases. If we define Δv as the shift in frequency from its value at one atmosphere and 25°C in each solvent, Δv at the maximum pressure varies from 11 cm‐1 in 2, 3 dimethyl butane to 41 cm‐1 in n‐propyl iodide. The frequency shift is found to be a linear function of the square of the density and the polarizability of solvent bonds, though this latter relationship is not quantitative. The shifts are plausibly explained as due to van der Waals' forces between the O–H bond and the solvent. The pressure causes a large increase in the polymerization of the alcohol, from which the change of volume on polymerization is estimated to be —4.64 cm3/mole in the 1 to 5820 atmosphere range, and —2.47 cm3/mole in the 5820 to 11 330 atmosphere range.

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