Dielectric and conformal studies of 1-propanol and 1-butanol in methanol.

Hydrogen bonds in small chain alcohol-alcohol binary systems alter the dielectric permittivity of the binary system. With a view to obtain a better understanding of the interactions in such systems, the complex permittivity spectra of mixtures of methanol (ME) with 1propanol (1PR) and 1butanol (1BU) have been measured in the frequency range 10 MHz to 20 GHz using time domain reflectometry at 288 K, 298 K, 308 K and 318 K. The dielectric parameters such as static dielectric constant and relaxation time were obtained using the calibration method based on nonlinear least squares fit method. Using these parameters excess permittivity, excess inverse relaxation time, Kirkwood correlation factor, and thermodynamic parameters were determined. It is observed that the static permittivity decreases with increase in mole fractions of 1PR/1BU in ME whereas the relaxation time increases for both the binary systems. Computational conformational analysis was performed using ab initio Hartree-Fock using Gaussian-03 program. The present studies indicate a difference in the solvation of ME by 1PR/1BU and vice versa. Further, the interaction of ME-1PR is distinctly different at the 0.55 molar concentration of 1PR while the ME-1BU system shows strong interactions in both the methanol and the 1BU rich regions.