Étude par Spectrométrie Infrarouge de la Complexation de Phénols Substitués par la Triéthylamine

Complexation constants of hydrogen bonded complexes between substituted phenols and substituted pyridines were determined by infrared spectroscopic measurements in carbon tetrachloride at 25OC. It was previously shown that for monosubstitutedJcomplexes the complexation constant Kab obied the relation log KOb = log Ko+pu where u is the Hammett substitution constant. When both the proton donor and the proton acceptor are substituted, it is shown in the present work that the logarithm of the complexation constant can be expressed by the equation:where KO, refers to the unsubstituted complexe phenol-pyridine: p: is the pa value when ub is zero and p$ the pb value when a,, is zero. The product &,pb is an interaction term where B = -037. This relation shows that an increasing acidity of phenol enhances the substitution effects on the pyridine. This interaction term is discussed in terms of dipolar and polarisation effects. A similar equation was previously found for the phenol-aniline disubstituted complexes. In the present case, the p: and p: values are greater owing to the stronger basicity of pyridine, and to the smaller O . . . N distance. The E constant however is greater with the aniline (-1.70) than with the pyridine complexes. This fact is discussed in terms of the variation of hybridization of the nitrogen atom in the complexes, which in the case of aniline, can be deduced from HNH angle measurements.

show abstract

Contribution A L'Étude du Spectre D'Absorption Électronique de Complexes Phenols‐Triéthylamine

Dupont

Dhondt

Zeegers‐Huyskens

1971

Bulletin des Soc Chimique

Self Cite

View full text Add to dashboard Cite

The hydrogen-bond complexes formed by substituted phenols ( p K . from 10,25 to 6 ) and triethylamine are studied in cyclohexane solution at 25 " C , by electronic absorption spectrometry. The formation constants of the complexes of 1 : I stoichiometry are determined by an algebric transposition of the Rose-Drago method. The constants ( K ) obey the Hammett relation log K = 1,51 Z u H + 1,94 This equation may be compared to the expression found by infrared spectrometry, for the same complexes in carbontetrachloride log K = 1,30ZoH+1,73showing that the p factor of Hammett is greater in cyclohexane than in carbontetrachloride. The effects of complexation on the electronic transitions are discussed. The extinction coefficients, the oscillator strenghts and the displacements of the 0-0 transitions are determined for the 'Lb transition and in some case for the ' L , and 'B transitions. The complexation effects o n the sub-vibrational levels are discussed. For all the phenols studied, the complexation causes bathochromic and hyperchromic effects; these effects however are smaller than those produced by the introduction of a substituent into the phenolic ring.The wave numbers of the maxima of absorption of the phenolate ion in aqueous medium are compared with the wave numbers of the maxima of absorption of the complexes in a n aprotic solvent. The values are discussed in terms of formation and dissociation of ionic complexes.

show abstract

Étude par Spectrométrie Infrarouge de la Complexation de Phénols Substitués par la Triéthylamine

Cited by 9 publications

References 12 publications

Mise en évidence de complexes de stoéchiométrie 2:1 par spectrométrie infrarouge

Mise en évidence de complexes de stoéchiométrie 2:1 par spectrométrie infrarouge

Étude par Spectrométrie Infrarouge de la Complexation Entre les Phénols Substitués et les Pyridines Substituées

Contribution A L'Étude du Spectre D'Absorption Électronique de Complexes Phenols‐Triéthylamine

Contact Info

Product

Resources

About