By using DSC data, the enthaplies of sublimation for ethyleneurea and propyleneurea, are calculated as 84 and 89 kJ mol-1 respectively. Using the vaporization enthalpy values for dimethylethyleneurea and dimethylprophyleneurea, as obtained from literature, the empirical relation: <FONT FACE="Symbol">D</font>crg Hmo (1)/ <FONT FACE="Symbol">D</font>crg Hmo (2) = <FONT FACE="Symbol">D</font>lg Hmo (1)/ <FONT FACE="Symbol">D</font>lg Hmo(2) = constant, that relate sublimation or vaporization enthalpies of two different substances and of its methylated derivatives, is obtained. Correlations like that are found to another ureas and thioureas.
amides; sublimation enthalpy; vaporization enthalpy
