The Absorption Spectra of a Series of Organic Molecular Compounds.

Abstract

Pfeiffer (1) and others have investigated the colored molecular compounds resulting from quiñones with aromatic hydrocarbons, ethers, or amines. Pfeiffer has classified these compounds with the quinhydrones and has shown that a series extends from the intensely colored quinhydrones existing as crystalline compounds, through colored complexes difficult to crystallize, to complexes impossible to crystallize and identified largely by a slight color change on mixing the liquid components. These latter "molecular compounds" are tied by forces which are weak in comparison with the intermolecular forces in the crystals of the components, for, on cooling, the components of the mixture crystallize out separately. Foreign solvents tend to dissociate the compounds and as a result Beer's law does not hold.We undertook a spectroscopic study of the more weakly tied compounds of this type in the hope of extending the series of molecular compounds to loosely tied complexes which had escaped detection because the color change occurred in the ultra-violet or was too slight to be seen with the eye. There was also the possibility that the "solvent effect" of absorption spectroscopy could be linked with these color changes. Foremost, however, there was the hope that a correlation between color and oxidation-reduction potentials might be established. RESULTSWe have carried out quantitative light absorption measurements on the five quiñones-chloroquinone, benzoquinone, toluquinone, xyloquinone, and duroquinone-in a melted state and in the absence of any solvent.The resulting curves are compared with the light absorption of equimolecular mixtures of these quiñones with various aromatic ethers, hydrocarbons, and the junior author after the death of Dr. Hunter in 1931.-L. I. Smith.

Aromatic Molecular Complexes of the Electron Donor-Acceptor Type.

“…Many of these unstable complexes display no visible absorption but rather have been recognized through the appearance of bands in the ultraviolet or infrared spectra of solutions of two components which are not characteristic of the parent compounds. Hunter and Northey (149) were perhaps the first investigators to report measurements outside the visible region in the detection of complex formation. They observed that the ultraviolet spectra of thin films of solutions of quiñones in various simple benzene derivatives were shifted toward the visible as compared to the spectra of the fused quiñones.…”

Interaction of Quinones and Hydrocarbons Investigated by Microscopic Mixed Fusion Analysis

“…This could be due to factors affecting heats of fusion as mentioned previously or it could indicate a special effect of alkyl substitution on the quinone ring. In solution studies, alkyl substitution of the quinone ring has been reported to decrease the equilibrium constant for addition compound formation between oxygenated aromatics and quiñones (5).…”