ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Theoretical study on the heat of formation of some polycyclic aromatic hydrocarbons

Izudin Redžepović and Svetlana Marković

University of Kragujevac, Faculty of Science, Kragujevac, Serbia

E-mail: mark@kg.ac.rs

Received: 24 June 2019  Accepted: 22 August 2019

Abstract:

This paper reports the results on how structural details govern the heat of formation (ΔH_f) of the catacondensed benzenoid hydrocarbons, a wide subclass of polycyclic aromatic hydrocarbons. To accomplish this goal, the influence of the molecular size (expressed through the number of six-membered rings, N_R), number of bays (N_B), number of coves (N_C), number of fjords (N_F), and molecular branching (expressed through the number of B3-type rings, N_B3), as well as the position of the latter four structural features in a molecule were inspected. To obtain the ΔH_f values, the semiempirical PM7 method was applied, and it showed good agreement with the existing experimental results. These structural properties affect ΔH_f of these compounds differently. The strongest effect on ΔH_f has N_R, and it was found that ΔH_f increases with increasing N_R. ΔH_f also increases with increasing N_B3. However, when the molecular branching is moved across the molecule, it was found that ΔH_f decreases, as it moves to the middle of a molecule. ΔH_f of the examined compounds decreases with increasing N_B, N_C, and N_F, and as the bay, cove, and fjord move to the middle of a molecule. When N_B, N_C, and N_F take large values, this decrease slows down.

Keywords: Semiempirical method; Catacondensed benzenoid hydrocarbons; Thermodynamic quantity; Molecular structure

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-019-00914-7

Chemical Papers 74 (3) 829–836 (2020)