The Cyclization of Alkyl Side Chains of Naphthalenes: The GC/Potential Energies/FTIR Approach

Pavel Straka^1*, Miroslava Novotná², Petr Buryan², Olga Bičáková¹

¹Institute of Rock Structure and Mechanics, v.v.i., Academy of Sciences of the Czech Republic, Prague, Czech Republic.
²Institute of Chemical Technology, Prague, Czech Republic.

DOI: 10.4236/ajac.2014.514103                

Abstract

Gas chromatographic measurements of the retention times of alkyl naphthalenes on packed columns with polar and non-polar stationary phases have proven that the logarithm of the relative retention time increases bi-linearly (not linearly) with the number of carbon atoms in a molecule. This is caused by a strong inclination of alkyl side chains toward intramolecular cyclization. A FTIR spectral analysis has shown that longer alkyl side chains of alkyl naphthalenes are cyclized through an interaction between the terminal CH₃ group and the aromatic ring. Conventional aromatic-aliphatic molecules thus become new molecules with quasi-alicyclic rings. This, however, alters the effect of non-covalent van der Waals attractive forces both inside and outside the molecules, which is reflected in an exponential increase of the retention times of alkyl naphthalenes with a side chain longer than propyl and in the bi-linearity of the logarithmic dependence of the relative retention times on the number of carbons in the molecule.

Keywords

Alkyl Naphtalenes, Retention Times, Molecular Mechanics, van der Waals Forces

Conflicts of Interest

The authors declare no conflicts of interest.

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