Enthalpies of hydrogen bond formation between phenol and substituted pyridines are measured by calorimetry. The obtained energies are compared with the base ionization constants in water and the Q values of the pyridine substituents. The relation formation energy to infrared frequency shift is the same as for alcohols or phenols-pyridine complexes. Distances between 0 and N atoms linked by the hydrogen bond are related to the infrared frequency shift: it is then concluded that a linear relation exists, for the complexes studied, between the heat of formation and the bond distance. Influence of steric hindrance on the bond distance is discussed.La premikre partie de ce travail (I) a trait a I'ttude des chaleurs de complexation de la pyridine avec difftrents donneurs de proton. Les enthalpies de formation sont dttermintes connaissant lachaleur de mtlange de deux solutions dilukes de chacune des deux moltcules. Une mtthode analogue avait t t t appliquke a la complexation d'amines et d'alcools aliphatiques (').Une nouvelle strie de mesures, prtsentte dans cet article, poursuit l'ttude des chaleurs de complexation du phtnol avec des pyridines diversement substitutes. La constante d'tquilibre de complexation a tt6 d6terminte prtctdemment par spectroscopie infrarouge.Cette strie de complexes oh le donneur de proton reste constant montre dans quelle mesure les proprittts des complexes similaires a accepteur constant se trouvent vtrifites. L'effet sttrique des dtrivts ortho (*) Titulaire d'une bourse de spkialisation de 1'1 W O N L .
Heats of formation of Hydrogen bond complexes between pyridine and alcohols or substituted phenols are measured in carbon tetrachloride solution by calorimetry. The obtained energies are compared with the acid ionization constants in water and the a values of the phenol substituents. Steric hindrance lowers the bond energy. However the heats of complex formation are linearly related to the frequency shift of the hydroxyl absorption brought about by the Hydrogen bond interaction.
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