Infrared spectra of hydrogen bonded adducts of 2,6-dichlorophenols and oxygen bases

Abstract

This paper is dedicated to Professor Camille Sandorfy on the occasion of his 65th birthdayR. WOLNY, A. KOLL, and L. SOBCZYK. Can. J. Chem. 63, 3568 (1985). Infrared spectra of hydrogen bonded complexes of 2,6-dichlorophenol derivatives and oxygen bases have been studied over a broad ApK, range (from -10.55 to + 1.69). For the complexes of I : I stoichiometry typical evolution of spectra, similar to those for other hydrogen bonded systems, have been found. With an increase of ApK.,, the hydroxyl group stretching vibration band shifts to lower frequencies until the inversion region is reached, where hydrogen bonded (HB) and proton transfer (PT) forms occur in equilibrium, then a broad background absorption is observed. The centre of gravity of the broad protonic bands, v,,, calculated from the integrated intensity over the whole infrared region have been correlated with ApK. and the contribution of the PT form. It has been shown that the minimum on the plot v,, vs. ApK;, is reached close to the inversion point, where K, = I. The observed correlations and the change in the shape of the broad protonic absorption are consistent with expectations of theories based on the concept of the double minimum potential function and the stochastic mechanisms of band broadening.R. WOLNY, A. KOLL et L. SOBCZYK. Can. J. Chem. 63, 3568 (1985).Utilisant un large intervalle de ApK, (allant de -10,55 a + 1,69), on a etudie les spectres infrarouges des complexes des dCrivCs du dichloro-2,6 phCnol et des bases oxygCntes lies par des liaisons hydrogknes. Dans le cas des complexes du type I : I, on a trouvC une Cvolution typique des spectres semblable a celle des autres systkmes lies par des liaisons hydrogknes. Lorsque le ApK. augmente, la bande de vibration d'tlongation du groupe hydroxyle glisse vers les basses frequences jusqu'ii atteindre la rCgion d'inversion ob les formes hydrogkne liC (HL) et transfert de proton (TP) existent ii I'Cquilibre; on observe alors une large absorption de fond. On a Ctabli une correlation entre le centre de gravitC des bandes protoniques larges, v,,, calculC a partir de I'intensitC intCgrCe sur toute la rCgion infrarouge, avec le ApK;, et la contribution de la forme TP. On montre que I'on atteint le minimum de la courbe v,, en fonction du ApK;, prks du point d'inversion ob K,, = I . Les corrClations observCes et le changement de forme de I'absorption protonique large sont en accord avec les attentes des theories fondees sur le concept de la fonction de potentiel du minimum double et sur le mCcanisme stochastique de I'Clargissement de la bande.[Traduit par le journal]

Vibrational spectroscopic studies of hydrogen‒bonded complexes between 2,5‐dihydroxy‐P‐benzoquinone and amines

“…The inversion region is characterized by a number of anomalies such as: (i) unusual broadening of protonic IR bands [21], (ii) remarkable increase of their intensities [22], (iii) shift of the gravity center of the protonic vibration to extremely low frequencies [23] and (iv) particularly low values of the isotopic ratio [24] ν(OH)/ν(OD).…”