STRUCTURE, VIBRATIONAL PROPERTIES AND POLARIZABILITIES OF METHYLNAPHTHALENE ISOMERS. A QUANTUM-MECHANICAL APPROACH

Abstract

Geometries, barrier heights for rotation of the methyl group, infrared and Raman spectra and electronic and vibrational polarizabilities (⟨α⟩) of 1-and 2-methylnaphtalene isomers (1-MN and 2-MN) have been calculated by ab initio HF and MP2 methods, as well as by DFT-B3LYP functional, using 6-31G* and 6-31 + G* basis sets. Structural parameters and relative energies of MN isomers are dependent on electron correlation effects, the MP2/6-31G* theoretical level giving the best results. The methyl group of 2-MN is predicted to have a greater electrophilic affinity than that of the 1-MN isomer, owing to the lower acidity of its hydrogen atoms. Computed B3LYP/6-31 + G* ⟨α e ⟩ values of MN isomers are in excellent agreement with experiment, with deviations within 1%. In passing from 1-MN to 2-MN isomer, the increase of ⟨α e ⟩ is in some consistency with an observed increase of the biodegradation rates in aqueous systems, suggesting that polarizability plays an important function in the biodegradative process.