High Resolution NMR Studies of Chemical Shifts and Relaxation Time in quinoline, its Various derivatives and some of Metal complexes formed by its Hydroxyquinoline Derivatives

Abstract

The project is concerned with the Nuclear Magnetic Resonance NMR studies of chemical shifts, mostly proton and ᶦᵌC of quinoline and its various commercially available derivatives using high resolution NMR of 2.1,7.1 and 11.7 Tesla (T) fields. The study is related with solvent dependent proton ᶦH and ᶦᵌC shifts in the first instance. Proton spectra are very complex and shifts are strongly solvent dependent. These spectra need a theoretical analysis, so that experimental values can be assigned to the complex peaks. The theoretical analysis needs complex computer simulation program LAOCOON3 or 2-D analysis which has not been possible before. From the proton spectra published before at 200 MHz in dimethylsufoxide-d₆ (DMSO- d₆) solvent and the recently recorded spectra on chloroform-d solvent at 300 MHz, it is apparent that the shifts are sensitive to solvents. Polar solvents make hydrogen-bonds with nitrogen of quinolones, thus affecting the ¹H-shifts. ᶦᵌC are less sensitive to solvents. However the carbon atoms attached to nitrogen atom of quinoline and its derivatives are affected by various solvents. In high field only two solvents e.g. DMSO- d₆ and chloroform-d have been tried. In the present case the cheapest deuterated solvent chloroform-d has been used. Assignment of ᶦᵌC peaks on non-reported compounds has been done tentatively. Proper assignment requires 2-D NMR. For some compounds 2-D NMR has been reported. Quinoline derivatives which contain hydroxyl -OH group like 8-hydroxyquinoline are very important compounds. These are used in metal analysis and separation. Hydroxyl-OH group makes H-bonds and complexes with solvents and metals. For such compounds, a detailed H-bond study has been undertaken. This study has not been conducted on such important compounds before. The hydroxyl-OH peak in proton spectra of these compounds has not been reported in literature accurately. It exchanges with proton of solvent water and becomes broad and non-detectable. It makes H-bonds with polar solvents. Hydrogen-bond study needs non-polar solvents, like carbon tetrachloride CCI₄ and cyclohexane C₆H₁₂. For 8-hydroxyquinoline (oxine) and some of its derivatives. H-bonding study in CCI₄ used as non-polar solvent has been carried out. This study shows that proton shift of –OH group decreases with the decrease of concentration of these compounds in CCI₄. This is what one expects from such compounds. A quantitative treatment is required for which work is in progress. Proton and ᶦᵌC relaxation time study has been carried out on methyl-derivatives of quinoline at low field of 2.1 Tesla (89.55 MHz for proton and 22.5MHz for ᶦᵌC). The spectra of proton are complex but methyl group gives a single peak. Methyl group shows rotation nearly at all temperatures. In the present case study has been restricted above room temperature, where rotation is predominant. Relaxation time T₁ is recorded at various tempratures. Relaxation of proton follows usual behavior. ᶦᵌC predominantly follows dipolar relaxation mechanism. Various mechanisms have been separated from each other. Form variable temperature study energy barrier Eₐ hindering methyl group rotation has been calculated from both proton relaxation and ᶦᵌC dipole-dipole relaxation. The activation energy Eₐ obtained varies from 3.04 kcal/mol to 4.69 kcal/mol. Error limits for Eₐ have been given a comparison with similar compounds has been suggested.