The vapour pressures, latent heat of sublimation and associated entropy changes of eight anthraquinone derivatives, six diphenylamine derivatives and seven azobenzene derivatives have been measured by the Knudsen's effusion method. The heat of sublimation and associated entropy changes for two main derivatives of anthraqinone and diphenylamine is discussed in terms of molecular structure, based on the assumptions of additive property of energy and exsistence of hydrogen bond, and the following results have been obtained.
1. The heat of sublimation for 1:4-diamino- and 1-amino-4-hydroxy-anthra-quinones are 2 and 1.2 Kcal/mol greater than that of anthraquinone respectively.
2. The heat of sublimation of 1- and 2-aminoanthraquinones is 3.8 and 11.3 Kcal/mol greater than that of anthraquinone respectively, and an increase of these values is chiefly due to the intermolecular hydrogen bonds.
3. The heat of sublimation of 2-nitro- 4-nitro- and 2:4-dinitro-diphenyl amines is 2.2 and 7.8 Kcal/mol greater than that of diphenylamine respectively. and an increase of these values is due to the increase in polarity.
4. The heat of sublimation for 4′-amino- and 4′ hydroxy-2:4-dinitrodiphenyl amine is 1.8 and 5.3 Kcal/mol greater than that of 2:4-dinitrodiphenylamine respectively, and an increase of these values is chiefly due to the intermolecular hydrogen bond.