Th. Zeegers-Huyskens

Etude par spectrométrie infrarouge de la stoechiométrie des complexes phénols-triéthylamine

Resume The complexes formed between triethylamine and phenols have been studied by infrared spectrometry in carbon tetrachloride solution at 30°C. The phenols have been chosen so that their pKα vary from 10·30 to 3·50. The apparent complexation constant, calculated on the model of a 1:1 stoichiometric complex shows a marked variation with the concentration in free proton donor. Using a method based on the variation of this “apparent constant”, the equilibrium constants of 1:1 (K1) and 2:1 (K2) stoichiometric complexes have been determined. These values are related to the sum of the Hammett σ constants (Σσ) by the following relations: log K1 = 1.73 + 1.30Σσ log K2= 1.57 + 0.05 Σσ + 0.94 (Σσ)2 Log K1 is linearly related to Δμ, the increment of dipole moment, determined by Ratajcyak and Sobczyk, in benzenic solution. On the other hand, equation (2) is compared to an expression, obtained previously in the study of the complexation of substituted phenols-substituted anilines, showing that the logarithm of the complexation constant depends on an interaction term depending on the product of the substitution constants σaσb. The formation of a complex of 2:1 stoichiometry gives a characteristic vibration band lying at some 100 cm−1 lower than the dimeric phenol; this constatation is explained in terms of the greater basicity of the oxygen atom in the 1:1 complex than in the dimeric phenol. The CH stretching vibrations of the triethylamine are disturbed in frequency and intensity by the formation of a hydrogen bond; this perturbation increases with the phenol acidity.

Etude par spectrométrie infrarouge de l'interaction entre le N,N-diméthylacétamide et les phénols

Abstract The formation of 1:1 hydrogen bonded complexes formed by N,N-dimethylacetamide (DMA) and substituted phenols have Reen studied by infrared spectrometry in nonpolar solvents at 27°C. The complexation constants (K) calculated by this method obey the Hammett relationship. log K(1-mole−1) = 2,19 + 1,49ΣδH The value of the ϱ parameter is discussed in terms of the acid-base properties of the proton donor and the proton acceptor. A comparison is made with previously studied systems. The Δν(O-H) and Δν(CO) values are linearly related. The vibrational modea of DMA perturbed by complex formation with phenol and 4-Cl phenol are mainly some deformation and rocking vibrations of the methyl groups and the valence, in plane and out-of-plane deformation vibrations of the CO group. The vibrational modes of phenol perturbed by complexing with DMA are mainly the ν(O-H), δ(O-H) and γ(O-H) vibrations, four X-sensitive modes and some vibrations of the phenolic ring. These shifts are discussed in terms of electronic charge-transfer effects.

Étude par spectrometrie infrarouge de la complexation de l'aniline

Resume The infra-red spectra of the complexes formed between aniline and different hydroxylic compounds have been studied. The aliphatic alcohols and phenols have been chosen so that their p K a values vary from 17·60 (tertiarybutanol) to 0·8 (picric acid). In carbon tetrachloride solution and with proton donators from tert -butanol to p -nitrophenol, the molecules form normal hydrogen bonds. The OH … N stretching frequencies were examined. The antisymmetric and symmetric stretching vibration of the NH 2 group of aniline are perturbed by the hydrogen bond. This perturbation varies for the asymmetric stretching vibration, from 32 cm −1 for tert -butanol to 75 cm −1 for p -nitrophenol, and for the symmetric stretching vibration from 28 to 60 cm −1 . In the same solvent, we have studied the complexes of aniline with trichlorophenol, pentachlorophenol, 2–6 dichloro-4-nitrophenol and 2:4 and 2:6 dinitrophenol. These molecules are not hydrogen bonded; the OH … N vibration and the perturbation of the NH 2 group disappear. Our results suggest the existence of electron-donor—acceptor complexes of the type existing in similar molecules, without hydroxylic function. In the solid phase the infra-red spectra of the complexes formed by aniline with the chlorophenols and dinitrophenols show a large band lying between 2900 and 2100 cm −1 , characteristic of the NH + … O − vibration. This shows that the complexes are in the ion pair form. The chlorophenols studied show one or two narrow bands at about 3300 cm −1 , suggesting the existence of a free NH group, perturbed by the hydrogen bond and the crystal forces.

Application des relations de Taft à la complexation

Abstract By infra-red spectrometric measurements, the constants for complex formation (K) of phenol with several primary (I), secondary (II) and tertiary aliphatic amines (III) have been determined in carbon tetrachloride solution at 27°C. The plot of log K in function of the sum of the polar substituent constants of Taft, Σ σ*, give approximately a straight line, but no linear relation was found for secondary and tertiary amines. Taking into account, the sum of the Taft steric factor, Σ Es, the following equations were found: for system I: log K = −1·07 Σ σ* + 0·13 Σ Es + 2·56 for system II: log K = −0·80 Σ σ* + 0·25 Σ Es + 1·97 for system III: log K = −0·38 Σ σ* + 0·44 Σ Es + 1·84. As found previously by Hall, the pKa of aliphatic amines in aqueous solution depends only on the sum of the polar constants, but the coefficients are different for the three classes of amines. In this optic, the theory of solvatation of Trotman—Dickenson and the calculations of Folkers and Runquist, and Condon are discussed. The difference between the complexation and the ionisation can be explained by two factors: 1. (a) The molecule of phenol has a greater steric hindrance than the molecule of water and the approach of this first molecule to the nitrogen atom is more difficult; 2. (b) The distances O…N in the complex and the distance N+H…O− in the ion are different. The average N+H…O− distance given by Pimentel is about 2·80 A. It was shown previously that, in the complex formed by phenol with propylamine, the O…N distance is about 2·53 A. These facts can explain the sensitivity of complexation to steric factors. In this optic, we may remark that Bayles and Chetwyn have determined the complexation constants of 2–4 dinitrophenol with mono-, di- and tributylamine in an aprotic solvent. The complex is in the ionic form (formation of a NH+…O− bond) and the order of the complexation constants is: amine 3 > amine 2 > amine 1.

Étude par spectrométrie infrarouge de la complexation entre les phénols substitués et les anilines substituées—II: Perturbation des vibrations de valence 1 νNH2

Abstract The frequencies of the fundamental νNH2, stretching vibrations of several anilines complexed with phenol, 3,5 dichlorophenol, p-nitrophenol and 3-CF3, 4-NO2 phenol are determined in carbon tetrachloride solutions. The asymmetric and symmetric vibrations are shifted to lower frequencies by complex formation and the magnitude of the perturbation depends on the acidity of phenols and on the basicity of anilines. The non-complexed anilines are characterized by an increase of the H-N-H angle and of the N-H force constant when the electrophilic power of the substituent is more pronounced. These facts are explained by Mason in terms of an increasing s character of the N-H bonds, of a more important delocalization effect into the aromatic ring and of an increasing electronegativity of the nitrogen atom. In the complexes phenol-anilines, the H-N-H angle increased about one degree when going from m-anisidine to m-Cl aniline; the force constant also increases slightly, but in the 3,5-dichlorocomplexes, the angle and the force constant are practically unchanged. This fact may be explained by two concurrent effects: the increasing acidity tends to increase the angle whereas the complexation tends to diminish it. These two effects contribute both to decrease the electronic density around the nitrogen atom. The variation of the force constant in function of the percentage of the s character has a maximum value for a tetraedric hybridization.