The formation of quasi-alicyclic rings in alkyl-aromatic compounds

Abstract The alkyl side chains of n-alkyl phenols, n-alkyl benzenes and n-alkyl naphthalenes are cyclised, as demonstrated by GC measurements, FTIR spectroscopy and molecular mechanics calculations. Cyclisation occurs due to the intramolecular interaction between an aromatic ring ( -δ ) and a hydrogen of the terminal methyl group (+ δ ) of an alkyl chain. In fact, conventional molecules are not aliphatic–aromatic, but quasi-alicyclic–aromatic. With the aromatic molecules formed with a quasi-alicyclic ring, the effect of van der Waals attractive forces increases not only intramolecularly but also intermolecularly. This effect is strong in molecules with propyl and higher alkyl substituents. The increase of intermolecular van der Waals attractive forces results in bi-linearity in the GC retention time of the compounds in question, observed in the dependence of the logarithm of the relative retention time on the number of carbons in a molecule in both polar and nonpolar stationary phases with both capillary and packed columns. The role of van der Waals forces has been demonstrated using the potential energies of covalent and noncovalent interactions for 2- n -alkyl phenols, n-alkyl benzenes and 1- n -alkyl- and 2- n -alkyl naphthalenes.