Volumetric properties of tetraphenylporphyrin and some of its alkoxy and tert-butyl derivatives in tetrachloromethane solutions

Densities, apparent molar volumes, and partial molar volumes, V20, of tetraphenylporphyrin, H2TPP; meso-tetra-4-alkoxyphenyl porphyrin derivatives, H2T(4-OCnH2n+1)PP (where n=4, 6, 8, 10, 12, 16); meso-tetra-4-tert-butylphenyl porphyrin, H2T(4-tBu)PP; meso-tetra-3,5-ditert-butylphenyl porphyrin, H2T(3,5-tBu)PP, in tetrachloromethane (TCM) solutions at 25 °C were determined. For TCM and benzene solutions of the compounds examined, relationship ΔK=K2−K1 was established as a function of van der Waals volume V2W, where K2=V2W/V20 and K1=V1W/V1* represent the packing coefficients of the solute and the solvent (V1* is molar volume of solvent), respectively. The resulting correlations were compared with the correlations established for members of various homologous series like n-alkanes, cycloalkanes, crown-ethers, cage structures. The ΔK-value was found to be closely related to the geometry of the solute molecule. Relationships are also given which relate V20 with the number n of the structural repeating units (methylene groups) in compounds H2T(4-OCnH2n+1)PP, n-alkanes, cycloalkanes, and crown-ethers. An attempt was made to interpret the solvation properties of the solutions of individual compounds in the homologous series and also the similarities and differences between the homologous series.