Dipole Moments of 4-n Alkyl-4′-Cyanobiphenyl Molecules (from OCB to 12CB) Measurement in Four Solvents and Theoretical Calculations

We report here a detailed description of our measurements on dielectric constants in nCB molecules highly diluted in four different solvents: cyclohexane, n hexane, benzene and carbon tetrachloride. From those experimental values we deduce at infinite dilution apparent values of molecular dipole moments μ. The study of the variation of μ versus the number n of carbon atoms in the alkyl tail shows that in the first two solvents variation for n greater than 6 is different from variation for n lower than 6; on the other hand no significant difference is observed in benzene and carbon tetrachloride. These results are commented upon and theoretical calculations are executed in order to search for a coherent explanation. Two kinds of calculation have been undertaken: molecular energies with Molecular Mechanics method and molecular dipole moments with D.I.D. method.