Volumetric, refractive and FT-IR behaviour of β-pinene with o, m, p-cresol at 303.15, 308.15 and 313.15 K

- Dominance of similar molecules (cresols) on mixing gives a positive contribution to VE
- Non-specific physical interaction between dissimilar molecules also gives a positive contribution to VE
- Specific interaction between dissimilar molecules (H-bonding etc.) gives a negative contribution to VE
- Interstitial accommodation due to difference in molar volume and free volume between unlike liquids also gives a negative contribution to VE

Density (ρ) and refractive index (nD) of binary mixtures of β-pinene with o, m, p-cresol have been measured over the entire composition range expressed by mole fraction (x1) and volume fraction (ϕ1) of the β-pinene at 303.15, 308.15 and 313.15 K at atmospheric pressure. The FT-IR measurements were carried out at 298.15 K. From the experimental data, excess molar volume (VE), deviation in refractive index (ΔnD) and deviation in molar refraction (ΔRm) have been calculated and fitted to the Redlich-Kister polynomial equation. The excess or deviation parameters were plotted against mole fraction or volume fraction of the β-pinene over whole composition range. The observed negative or positive values of excess or deviation parameters were explained on the basis of the intermolecular interactions present in these mixtures. A comparative study of mixing rules namely Arago-Biot, Dale-Gladstone, Lorentz-Lorenz, Eykeman, Weiner, Heller, Newton, Oster and Eyring-John has been carried out to test their validity for these binaries over entire mole fraction of β-pinene at three temperatures. Comparison of various mixing rules has been expressed in terms of average deviation. The FT-IR study reveals that complex formation becomes maximum at 0.3 mole fraction of β-pinene, which is also supported by the VE and ΔnD data. The position and pattern of intensity of OH bands as per FT-IR data strongly supports the conclusion that molecular association through H-bonding has taken place.