The dielectric constants of the liquid mixtures piperidine/tetrahydropyran, piperidine/cyclohexane, and tetrahydropyran/cyclohexane have been determined in the temperature range 20 to 60 $^\circ$C. They have been used to evaluate Kirkwood's g-factor for the last two systems, and, for the tetrahydropyran/cyclohexane system, dipolar contributions to the excess thermodynamic functions of mixing, which have also been calculated for the chloroform/carbon tetrachloride system. The heats of mixing of the above systems have been determined (at 20 $^\circ$C) in order to compare the strengths of the various types of molecular interaction involved. All the mixtures are formed endothermally, suggesting that N-H$\ldots$O hydrogen bonds formed in the first system are weaker than the N-H$\ldots$N bonds solely present in the second, which has the largest excess enthalpy of the three systems. Nuclear magnetic resonance spectra have provided evidence of the formation of these hydrogen bonds.