Spectroscopic studies of orientational interactions between straight-chain alkanes and aromatic hydrocarbons

Abstract

Spectral shift measurements of u.v. absorption spectra of aromatic hydrocarbon soluted in alkane solvents show that the shift is systematically larger in normal alkanes that in the corresponding branched isomers. This result is related to the short range order existing preferentially in n-alkane liquids and is interpreted as a mutual orientation between solute and solvent molecules, resulting in maximum interaction. These oriented interactions are confirmed by theoretical calculations and an interesting correlation is made with the specific adsorption of n-alkanes on the graphite basal planes. Absorption and emission spectra of aromatic hydrocarbon doped n-heptane single crystals, exhibit a strong dichroic effect, again showing a high degree of orientation of the solute molecules in the lattice.