Spectroscopic observation of solvent interaction with selected retinal Schiff bases.
Iodide salts of several N-retinylidenedialkylamines were prepared and their UV-VIS spectra recorded. Their lambda max values increased as the number of hydrogen atoms on the carbons alpha to nitrogen increased. In separate experiments, iodide salts of N-retinylidene-n-butylammonium (1) and N-retinylidene-n-butylmethylammonium (2) were prepared, and their excitation energies (delta E) were measured in selected solvents of varying dielectric constant (epsilon). Data from each compound gave a straight line which converged at epsilon = 0. On the other hand, when delta E values of the iodide and bromide of 2 were plotted vs solvent epsilon, parallel rather than convergent lines were obtained. When lambda max values of 1 and 2 were measured in a greater number of solvents, the solvents fell into four main groups. The first group, regular solvents, are rigid, have fixed dipoles, neither donate nor accept H-bonds, and the delta E of 1 and 2 decreases linearly as solvent epsilon increases. This line for 2 is taken as a standard against which other solvents are judged. A second class of solvents that are good H-bond donors like CHCl3, whose dipole moment coincides with the C-H bond axis, is located in an area below the standard line. A third group, nucleophilic solvents like tetrahydrofuran, whose dipole moment is coincident with a strongly nucleophilic oxygen atom are good H-bond acceptors and are found above the standard line. Solvents with unpredictable spectroscopic behavior are classed as anomalous.
Blatz
P E
PE
School of Basic Life Sciences, University of Missouri-Kansas City 64110.
Mohler
J H
JH
Ahmed
W
W
D001965:Bromides; D007454:Iodides; D012044:Regression Analysis; D012176:Retinoids / Q000737:chemistry*; D012545:Schiff Bases; D012997:Solvents; D013053:Spectrophotometry / Q000379:methods; D013329:Structure-Activity Relationship
D001965:Bromides; D007454:Iodides; D012176:Retinoids; D012545:Schiff Bases; D012997:Solvents