Analysis of IR Vibrational Spectra of Isomeric Butanediols in Inert and Proton Acceptor Solvents

D. I. Abaidullina ; M. A. Varfolomeev ; B. N. Solomonov

Učënye zapiski Kazanskogo universiteta. Seriâ Fiziko-matematičeskie nauki, Kazanskii Gosudarstvennyi Universitet. Uchenye Zapiski. Seriya Fiziko-Matematichaskie Nauki, Tome 151 (2009) no. 1, pp. 8-16

Résumé

Investigation of the aliphatic systems able to form intramolecular hydrogen bonds and intermolecular interactions in condensed media is a complex and actual question. The description of intermolecular interaction mechanisms could contribute to the solution of important problems, such as carbohydrate self-association mechanism investigation, molecular recognition and new substance synthesis. The carbohydrate identification with bio receptors occurs by lots of weak interaction (among them are H-bond and van der Waals interactions) formation. However, there are no methods allowing to analyze them separately. IR-spectroscopy is one of the most universal methods for investigation of different types of non-covalent interactions. However, in order to obtain correct results, proper analysis methods should be developed and tested on simple objects. The investigation of solvent effects on intra- and intermolecular hydrogen bonds in 1,2-, 2,3-, 1,3-, 1,4-butanediols and its complexes with proton acceptors was carried out in this work. Analogies and differences of intramolecular H-bond formation of studied diols by IR OH-stretching vibrations characteristics were analyzed. The solvent effect on IR frequencies of free and self-associated O–H-groups of studied alcohols was described. It was shown that intramolecular H-bonds strength and stability depend on the size of cycle formed by intermolecular H-bonding and the OH-groups in butanediol molecule location. Linear dependency between cycle size and strength of intramolecular hydrogen bond in 1,2-, 1,3- and 1,4-butanediol was observed, except data for 2,3-butanediol. Stability of these hydrogen bonds in opposite side is changed. This fact was confirmed by relation of intensities of H-bonded and free O–H-groups. Analysis of solvent effects on frequencies of O–H-groups H-bonded with proton acceptors was carried out. It was shown that values of frequencies of intramolecularly H-bonded butanediols in aprotic solvents were described by solvent parameter $S_{VW}$ responsible for van der Waals interactions. In proton donor solvent, like chloroform, intramolecular hydrogen bonds are strengthened (about 30%) due to cooperative effects. It was found that structure and composition of butanediols H-bonded complexes depend on solvent proton acceptor affinity and the diol concentration. For strong proton acceptors, quantity of intramolecularly H-bonded O–H-groups decreases with increase of diol concentration. For weak bases the relation between these species is practically not influenced by diol concentration.

Détail

Keywords: intramolecular hydrogen bond, IR-spectroscopy, butanediols, frequency, intensity, van der Waals interactions, proton acceptor ability, cooperative effects with diol concentration.