Jacques Corset

Anion solvation III. Infrared spectroscopic determination of solvent acceptor numbers and their use in understanding anion solvation

It is shown that the Gutmann acceptor number determined by NMR for a number of solvents correlates with vibration frequencies of these solvents. Vibration spectroscopy is applied to the determination of acceptor numbers to characterize the solvation of anions. The acceptor number obtained by this method characterizes the anion solvation in all its states of association with the cation.

Anion solvation II. Solvation of thiocyanate and halide anions in mixtures of protic and aprotic solvents

Infrared and Raman spectra of tetraalkylammonium and lithium thiocyanates and bromides in protic-aprotic solvent mixtures have been recorded in the 2100–2300 cm−1 region at room temperature. It is shown that the anion is hydrogen bonded to the protic solvent, whether free or linked to a cation. Models are given for the solvated ion-pair taking into account both anion and cation solvation.

Spectres de vibration du pivalate de méthyle — comparaison des fréquences caractéristiques du groupement ester méthylique pour une série d'

Abstract Infrared and Raman spectra (3600–3620 cm −1 ) of methyl pivalate (CH 3 ) 3 CCOOCH 3 (h 3 ) and (CH 3 ) 3 CCOOCD 3 (d 3 ), in the liquid and crystalline states have been recorded. It is concluded that methyl pivalate yields only one conformation in the temperature range studied. Vibrational assignments are proposed in terms of group frequencies and methyl ester group frequencies are compared in several molecules.

Anion solvation I. Solvation of the thiocyanate anion in aprotic solvents by near infrared spectroscopy

Solutions of tetrabutylammonium and lithium thiocyanates have been examined in the infrared 2000–5500 cm−1 region at room temperature. New bands have been observed which can be assigned to simultaneous transitions between the v (CN) vibrations of the anion and the v (CH) vibrations of the solvent CH3 group. These transitions which are independent of the state of association (free ion, ionpairs, dimers, triple cation) provide evidence of anion solvation by aprotic solvents.

Phenol solvation and states of aggregation of tetraethylammonium halides in carbon tetrachloride. Far and mid infrared study

Abstract The spectra of mixtures of tetraalkylammonium halides and phenol in carbon tetrachloride have been compared in the mid and far infrared regions. The salts exist in CCl 4 in large aggregates which are dissociated by phenol into ion pairs hydrogen bonded to phenol and multisolvated anions.

Dielectric and raman spectroscopic studies on the rotational isomerism of t-butyl formate

Abstract Static dielectric constants, refractive indices and densities have been measured for t-butyl formate and acetate in cyclohexane at increasing concentrations and at two temperatures, 20°C and 60°C. The Δ H value for the cis-trans equilibrium of t-butyl formate and the dipole moment of the trans conformation has been calculated from the dielectric measurements taking the Δ S value calculated from the sum-over-states for the cis and trans conformations and assuming the dipole moment of the cis conformation to be equal to 1.94 D as found for t-butyl acetate, which has the cis conformation only. The relative intensities of the Raman bands corresponding to specific vibrations modes of the cis and trans conformations of t-butyl formate are measured in cyclohexane and acetonitrile at various concentrations. The enthalpy difference Δ H is also measured in the liquid state and in acetonitrile by variation of the intensity ratio of the bands with temperature. All thermodynamic quantities obtained from dielectric or Raman intensity measurements are compared with each other and with the theoretical values. The solvation energy difference between cis and trans conformations in cyclohexane and acetonitrile as well as in the liquid state are also compared with theoretical values. The large deviation of solvation energy difference between the experimental value and Onsagers model value are well described by an additional term, which considers dipole-dipole interaction.

Formation of phosphonoacetate carbanions by lithiated bases or by the conjunction of a lithium salt and an amine: structural study of intermediate species

In THF, the anionic species (2) formed from methyl diethylphosphonoacetate (1b) by the action of Li bases coexist as aggregates (2A) and externally solvated monomeric ion pair (2M), while in CH3CN triple ions (2T) and small amounts of free ions (2–) are also characterized. When (1b) is in slight excess, relative to the lithiated base, these four species coexist in both solvents, together with other species (I). From n.m.r. and i.r. data, it appears that the intermediate species (I) include a neutral phosphonate (1b) moiety, as a Li+ cation bidentate ligand, the two other lithium solvation sites being occupied either by (2–), or by (1b) as a monodentate and a solvent molecule, or else by two solvent molecules. The structure of (1b) in this intermediate species is strongly perturbed as deduced from variations in 31P and 13C carbonyl shifts as well as that of νco. Furthermore, a fast proton exchange takes place between the anionic species (2) and free (1b) as shown by 1H n.m.r., but (I) does not participate in this exchange phenomenon. When (2) is formed by action of diazabicycloundecene (DBU) in the presence of LiCl, aggregates (2A), monomeric ion pari (2M), and small amounts of (2T) as well as two intermediate species (I) are characterized by i.r. or 31P n.m.r. spectroscopy. The role of DBU is manifold: it deaggregates LiCl or (2A), it deprotonates (1b) within (I), and it facilitates proton exchange between (2) and (1b), the relative importance of such effects depending upon the DBU concentration.

Infrared and Raman Studies of Interactions between Salts and Amides or Esters

The surrounding medium may play an important role in the activity of biological macromolecules. The action of salts, among others, may modify the macromolecular conformation, such as for gelatin, lithium bromide induced mutarotation of polyproline (Ramachandran, 1967; Von Hippel, 1969), or conformational changes of polyglycine (Baron, 1973). The ion transfer through membranes takes place through antibiotic-salts interactions (Mumoz et al., 1972; Ovchinnikov and Ivanov, 1975). These biological molecules may be either polypeptide chains, as in proteins, or chains with alternate ester and peptide groups, as in depsipeptides, or cyclic ethers and methyl esters. We therefore thought it of interest to start an investigation, through infrared and Raman spectroscopy, of the interactions between some esters and amide molecules and alkaline Earths or alkaline salts. Infrared and Raman spectroscopy are well adapted for studying short life interactions, and Raman laser spectroscopy makes it possible to examine aqueous solutions. On certain points the present work cross-checks the results obtained from quantum chemistry calculations (Pullman, 1974; Perricaudet, 1973). We shall first show how the organization of carbonyl groups around the cations may be determined through infrared and Raman spectroscopy. We shall then discuss the nature of interactions between cations and these molecules.