Studies of linear correlation factor of dielectric polarization and excess dipolar free energies of amides in apolar solvents

The Kirkwood-Frohlich correlation factor (g), Eyring’s parametersG and G^* and the dipolar excess free energies of dilute solutions of formamide, acetamide,N-methyl acetamide,N,N-dimethyl formamide andN,N-dimethyl acetamide in 1,4-dioxan/benzene were obtained from a measurement of their static dielectric permittivities at 308 K. The fluid structure of these amides is discussed. Both in formamide and acetamide a dimeric linear chain with the individual dipoles more or less parallely oriented is preferred. InN-methyl acetamide, the antiparallel orientation of dipoles at lower concentrations turns into a parallel orientation with increase of concentration. In tertiary amides, with increase of concentration, parallel orientation of dipoles with global value ofg tending to unity is observed. The dipolar excess free energy of mixing in a given solvent is of the order primary amide > secondary amide > tertiary amide.