Computation of Molecular Free Length (L f ) and Molecular Radius (M r ) of p-n-Alkoxy Benzoic Acids

Abstract

Dilatometric (density, ρ) and optics (refractive index, n) studies are utilized for the computation of thermoacoustic parameters, molecular radius, and intermolecular free length of p-n-alkoxy benzoic acids (nbas). For the estimation of Lf , the parameters like V 0, molar volume at absolute zero, and (Va ), the available volume is calculated from thermodynamic parameters. Further, V 0 can be obtained by the extrapolation of temperature variation of molar volume in isotropic phases to absolute zero. The molecular radius (Mr ) is obtained from the density and refractive index. The computed values using different methods are compared with one another as well as with the body of the data available. The temperature variation of different thermoacoustic parameters like Moelwyn-Hughes (C 1), reduced molar volume (V ∼), isochoric temperature coefficient of internal pressure (X), etc., calculated using different expressions are also presented. The increment in the molecular radius per methylene group in this homologous series is found to be 0.084 Å from density data and 0.054 Å from optics data. Further, it is observed that the Mr values obtained from optics data are found to be less compared to those obtained from density results. The Lf values estimated from different methods are found to show a similar type of variation with the chain length. However, the values differ slightly from one another and refinement is needed in the expressions to get concurrent results from different experimental data.