Sublimation Enthalpies of Substituted Pyridine N- Oxides.

The enthalpies of sublimation of five substituted pyridine N- 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 ₃ →NO ₂ →OCH ₃ . A difference is noted in the nature of dissociative ionization of disubstituted derivatives 2-CH ₃ -4-NO ₂ PyO and 3-CH ₃ -4-NO ₂ PyO. The relationship between the packing of molecules in crystals and the Δ H ° _subl values is considered.
Competing Interests: No conflict of interest was declared by the authors.
(© Pleiades Publishing, Ltd. 2021.)