Alfred Kolbe

Diorganothallium-übergangsmetall-komplexe, R2Tl—Mln

Abstract Diorganothallium transition metal complexes of the general formula R 2 Tl—ML n with ML n = M(CO) 2 LCp (M = Mo, W; L = CO, PPh 3 ) are obtained by protolytic reactions, redistribution reactions or by methatetic reactions, and are characterized spectroscopically and by chemical reactions. For ML n = Cr(CO) 3 Cp, Fe(CO) 2 Cp and Co(CO) 4 R 3 Tl and Tl(ML n ) 3 can always be isolated. In the case of Me 2 Tl—M(CO) 3 Cp (M = Mo, W) variable temperature NMR measurements gave evidence for a symmetrisation—redistribution equilibrium 3 R 2 Tl—ML n —ML n ⇌ R 3 Tl + Tl(ML n , which generally determines the stability of the diorganomthallium transition metal complexes.

Intramolecular Hydrogen Bond Interaction in Selected Diols

Abstract Solute descriptors characterizing major interactions in solution are accessible based on quantitative structure-property relationships (QSPR). Parameters of such relationships should be additive for functional groups. Because added parameters of monools describing molecular interaction do not meet the experimentally found intermolecular interaction parameters of diols and triols, it is assumed that intramolecular hydrogen bonding is responsible for these deviations. In this paper the intramolecular interactions in several diols are illuminated by IR measurements. Particularly, the influence of intramolecular hydrogen bonding on the absorbances of the OH groups is subject of investigation. Two conclusions can be drawn from the results: The terminal OH groups, which underlie an OH–OH interaction, also change their absorbance intensity in comparison to the free OH band. Secondly, the intermolecular interaction potential is strongly affected by intramolecular hydrogen bonding. The first observation is tentatively quantified as well as the position of the equilibrium between intramolecularly bonded and free diols.

Molecular interactions in conjugates of dicarboxylic acids and amino acids

Abstract Vibrational spectroscopic studies have been performed to obtain information regarding intermolecular forces acting in conjugates formed by dicarboxylic en-acids (fumaric acid, maleic acid) or their monobenzyl esters with esters of amino acids in the crystalline state and in solution. –NH groups, –COOH groups, and COamide groups have turned out to be the preferred carriers of those molecular interactions, which are the driving forces to form associates. These associates are mostly different in the crystalline state and in solution. The dimerisation of the molecules via the –COOH groups is suppressed in the preponderate number of cases in these molecular arrangements. The different behaviour of the substances is discussed in detail.

Influence of molecular interactions on the stability of hydrogen-bonded dimers of carboxylic acids

Abstract Possibilities to change the molecular arrangement of hydrogen bonded dimers of carboxylic acids by offering other acceptor groups are investigated in different species of molecules, namely in amino acid conjugates, in sulfinyl- and phosphinyl-carboxylic acids and in some p - n -alkoxybenzoic acids. As a result it was found that the carboxylic dimers are rather easily broken by lattice forces, by forming other intra- and intermolecular hydrogen bonds to stronger acceptor groups, and by increasing the temperature.

Solvent effect on the conformational behaviour of amino acid and oligopeptide derivatives

Abstract The solvent effect on acetyl amino acid methyl esters and C- and N-protected di- and tripeptide derivatives has been studied in deuterium oxide (D2O), 1.1.1.3.3.3-hexafluoroisopropanol (HFiP), dimethyl sulfoxide (DMSO) and methylene chloride (CH2Cl2). The interpretation is based on the amide I region. For the amino acid derivatives the relative shift of the amide I signal clearly indicates the strength of the interaction with the solvent molecules. However, in HFiP and DMSO solutions the occurrence of two overlapping signals for the amide I and the ester carbonyl signal, respectively, indicates the existence of two major conformers. Knowing the solvent effects on the small amino acid esters allows the assignment of the signals in di- and tripeptide derivatives. Although the identification of turn structures in these flexible molecules is not possible, the band positions and intensity of the deconvoluted amide I region clearly shows that certain conformers can be stabilised. It can be concluded that the band profile in the amide I region is determined by the number of amino acid residues linked in the molecule, the bulkiness of the side chains and their sequence and to a major extend by the solvent properties.

Molecular interaction study of some amino acid derivatives

Abstract Selected amino acid derivatives are investigated in order to obtain information about their intramolecular interaction, using infrared spectroscopy in the fundamental and overtone regions. A weak attractive interaction, responsible for the arrangement of the molecules in a five-membered ring, was found. Equilibrium constants for the intramolecular association were determined, with values between five and two. The interaction enthalpy was found to be close to zero.

Enantioselective effects in the association behaviour of optically active alcohols

Abstract The association behaviour of four optically active secondary alcohols with chiral C atoms in the α-position was investigated by means of IR spectroscopy and calorimetry CCl 4 was used as a solvent. As compared to the racemic compounds, the corresponding optically active alcohols have slightly higher concentrations of free OH groups, i.e. lower degrees of association, but somewhat higher enthalpy of association. Consequently, the H -bonding of racemic alcohols is favoured by entropy. Differences have been found also in the absorption coefficients of the associated OH groups. Optically active solvents exert some influence on the association behaviour of optically active alcohols. No differences could be observed in the H-bonding of optically active monocarboxylic acids, as compared with the racemic ones

Zum Schwingungsverhalten pentakoordinierter Zinn(IV)-organischer Verbindungen. IR- und Raman-Untersuchungen an 2,8,9-Tricarbastannatranen

SummaryResults are reported of IR and Raman investigations on four 1-substituted 2,8,9-tricarbastannatranes (1,X=Cl;2,X=Br;3,X=I;4,X=Me). Group-theoretic investigations confirm the trigonal-bipyramidal configuration of the tin atoms. The vibrational frequencies of the coordination (Sn←N) are correlated to the distancesd (Sn-N). Besides the results on the vibrations of the coordination polyhedrons other results are reported concerning the enantiomerization of the chiral atran skeleton.

Hydrogen bonding between pyrrole and amines

Abstract The association between pyrrole and several tertiary amines in different solvents has been investigated by means of ir spectroscopy. The results have been found in the order of magnitude as we had expected, but remarkable small differences have turned out between the interaction parameters of differently substituted pyridines and pyrrole. This behaviour suggests the existence of an additional interaction between aromatic amines and pyrrole.

Heteroassociation of Selected Diols with some Tertiary Amines

Abstract Diols exhibiting the structure (HO)CH2–(CH2)n–CH2(OH) with n=1 up to n=4, (HO)CH2–CH(OH)–CH3 and cyclohexan-1,2-diols as well as cyclohexan-1,4-diol, which may establish different intramolecular interactions, are used as model substances to describe the external hydrogen bonding behaviour of multivalent hydrogen bond donors in the presence of hydrogen bond acceptor molecules. In this study, hydrogen bonds formed by the diols with tertiary aromatic amines have been investigated. In solution, different associate formation between the diols and the acceptor molecules as sketched in Fig.1 may occur. Besides 1:1 associates formed by the interaction of one diol molecule with one amine molecule, 1:2 associates may be observed where each OH function interacts with one amine molecule. The equilibrium constants of the associates of those interactions have been studied by FTIR spectroscopy. The results allow a classification of the used diols in three different groups based on the position of the OH groups in the donor molecule. For diols with proton donating OH where no intramolecular hydrogen bond can be formed, the intermolecular hydrogen bonds for a 1:1 system may be described by thermodynamic parameters which are nearly twice the value of the corresponding equilibrium constants of monovalent alcohol systems due to the statistical weight of the OH groups. Secondly, when intramolecular hydrogen bond exists in the diols, the equilibrium constants in the interaction with the amine raise up by a factor of ca. 2–3 due to the cooperativity effect. Thirdly, if the OH groups are arranged in 1,2 positions, both OH groups may be described as independent of each other in their intermolecular interaction with the amine.