Dielectric enrichment in binary solvent mixtures. The intramolecular hydrogen bond in N-alkyl-substituted o-nitroanilines. Substituent effects

Abstract

In this work we report solvatochromism studies on o-nitroaniline and several N-alkyl-o-nitroaniline derivatives used as solutes in solvent mixtures of an "inert" nonpolar cosolvent, cyclohexane, and THF as a solvent with hydrogen bond acceptor ability. These studies allowed us to establish the competition between inter-and intramolecular hydrogen bond in solutes. This was done by comparing the magnitude of the local inhomogeneity induced by the solute-in-solvent mixture, that is, "preferential solvation," using Suppan's dielectric enrichment model as modified by us to be applied to electronic transitions. Since preferential solvation accounts for dielectric as well as specific interactions while dielectric enrichment only for the former, it was shown by comparison that it is possible to separate both effects and even quantify them. It was deduced that N-alkyl-o-nitroanilines form a strong intramolecular hydrogen bond, which remains unbroken even in polar solvents and hydrogen bond acceptors such as dimethyl sulfoxide. This was also confirmed by solvatochromic studies in pure solvents. On the other hand, a symmetrical dependence of the effects of alkyl substituents and solvents on the shifts of the absorption spectra was observed. [Traduit par la redaction]

Principles and Applications of Solvatochromism

“…8 Solvatochromic studies have been carried out using o-nitroaniline and severa l N -a lkyl-o-nitroaniline derivatives as solutes in solvent mixtures of an inert nonpolar cosolvent, cyclohexane, and tetrahydrofuran as a solvent with hydrogen bond acceptor ability. 9 Characterization of methanol/water and acetonitrile/water m ixtures has been carried out by a combination of solvatochromic and m ultivariate curve resolution methods. 10 In these studies, evidence has been found for form ation of mixed solvent complexes that play a role in the obser ved solvatochromic properties.…”

“…Over the past few years, the solvatoch ro m ic com p arison m etho d, which is based on the effect of solvent polarity on the electronic excitation energy of indicator dyes, has been used to successfully characterize various solvents. This method has also been applied to the characterization of systems such as mixed solvents, [3][4][5][6][7][8][9][10] dry solid surfaces such as silica, 11,12 silicalite and zeolites, 13 and alumina, 14 and also 'wetted' or 'solvated' solid surfaces, such as liquid ch ro m atog ra p hic stationar y bonded phases. 12,[15][16][17][18][19][20][21][22][23][24][25][26] This method has also been extended to supercritical uids [27][28][29][30][31] and to organized m edia such as cyclodextrins and micelles.…”

A New Organized Media: Glycerol:N,N-Dimethylformamide Mixtures/AOT/n-Heptane Reversed Micelles. The Effect of Confinement on Preferential Solvation

“…The solute surrounds itself preferably by the component in the mixture, which leads to the more negative Gibbs energy of solvation, as expected. 49 The observation that the solvent shell has a composition other than the macroscopic ratio is termed selective or preferential solvation. 33,35 Thus, QB seems to detect more GY molecules in its solvent shell than that corresponding to the bulk composition, and probably as a consequence the GY:DMF mixture is not ideal as it was previously demonstrated by other authors.…”

Solute–Solvent Hydrogen Bond Formation in the Excited State. Experimental and Theoretical Evidence

“…Thus, the solvatochromism of o-nitroaniline and N-alkyl-o-nitroaniline probes was studied in solvent mixtures involving an 'inert' non-polar cosolvent (CHX) and an HBA solvent (THF) [122,123].…”