Sublimation Enthalpies of Substituted Pyridine Oxides.

The enthalpies of sublimation of five substituted pyridine oxides were determined by the Knudsen effusion method with mass spectrometric control of the vapor composition within the framework of the second law of thermodynamics. The sublimation enthalpy of mono-substituted compounds 4-X-PyO depends on the nature of the substituent X and increases in the order CH→NO→OCH. A difference is noted in the nature of dissociative ionization of disubstituted derivatives 2-CH-4-NOPyO and 3-CH-4-NOPyO.