Pivalic acid in dilute solution of n-heptane and of CCl4 is studied via IR spectroscopy in the region of the C = O and O - H stretching fundamentals up to pressures of 2 kbar and temperatures of 175 °C. Lambert-Beer's law is shown to be valid for the C = O modes of the acid monomer and of the hydrogen-bonded cyclic dimer, which enables the quantitative measurement of the dimerization equilibrium as a function of pressure and temperature. Increasing pressure favours the dimerization in n-heptane to a larger extent than in CCl4 solution. In both solvents this pressure effect increases with temperature. The hydrogen bond strength within the dimer species is slightly reduced toward high pressure. The data on the temperature dependence of the dimerization volume and on the pressure dependence of the dimerization enthalpy are compared with direct information on both species as derived from their O - H fundamental modes.
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