Usage of the Y-Rule and the Effect of the Occurrence of Heteroatoms (N, S) on the Frontier Molecular Orbitals Gap of Polycyclic Aromatic Hydrocarbons (PAHs), and Asphaltene-PAHs

The understanding of the molecular- and colloidal-structure of asphaltenes has seen a major progress; however, there are still issues that require answer. One of them is the location of the heteroatoms in the polycyclic aromatic hydrocarbon (PAH) fused aromatic ring (FAR) region of asphaltenes. Therefore, the effect on the frontier molecular orbitals (HOMO-LUMO) energy-gap due to the addition of a heteroatom (N or S) to PAHs, which are candidates of the PAH region in asphaltenes, has been systematically analyzed by placing S or N in various sites of the PAH molecule. The S is introduced as a thiophenic ring in a bay region, while the N is introduced as a pyridinic-N, which are prevalent forms in the asphaltene-PAH. 174 PAHs are studied with five fused aromatic rings (5FAR) to 10FAR. The π-electron allocation in resonant π-sextets and isolated double bonds is obtained using the Y-rule. The frontier orbitals optical transition is calculated with the ZINDO/S method. Within a FAR family an increment of π-sextets produces and increase of the HOMO-LUMO energy-gap. There is a linear relationship between the Y-rule mapping (percentage of fraction of π-sextet bond divided by nFAR) and the HOMO-LUMO energy-gap. In addition, the effect on the frontier orbitals energy-gap and on the π-electronic allocation due to the presence of N and S is negligible; therefore, to reach conclusions related to the asphaltene-PAH based on conclusions reached for PAH systems, with no heteroatoms, is a reasonable approach.

Prediction of the Ultraviolet-Visible Absorption Spectra of Polycyclic Aromatic Hydrocarbons (Dibenzo and Naphtho) Derivatives of Fluoranthene

The annellation theory method has been used to predict the locations of maximum absorbance (LMA) of the ultraviolet-visible (UV-Vis) spectral bands in the group of polycyclic aromatic hydrocarbons (PAHs) C₂₄H₁₄ (dibenzo and naphtho) derivatives of fluoranthene (DBNFl). In this group of 21 PAHs, ten PAHs present a sextet migration pattern with four or more benzenoid rings that is potentially related to a high molecular reactivity and high mutagenic conduct. This is the first time that the locations of maximum absorbance in the UV-Vis spectra of naphth[1,2- a]aceanthrylene, dibenz[ a,l]aceanthrylene, indeno[1,2,3- de]naphthacene, naphtho[1,2- j]fluoranthene, naphth[2,1- e]acephenanthrylene, naphth[2,1- a]aceanthrylene, dibenz[ a,j]aceanthrylene, naphth[1,2- e]acephenanthrylene, and naphtho[2,1- j]fluoranthene have been predicted. Also, this represents the first report about the application of the annellation theory for the calculation of the locations of maximum absorbance in the UV-Vis spectra of PAHs with five-membered rings. Furthermore, this study constitutes the premier investigation beyond the pure benzenoid classical approach toward the establishment of a generalized annellation theory that will encompass not only homocyclic benzenoid and non-benzenoid PAHs, but also heterocyclic compounds.

Towards a taxonomy of topology for polynuclear aromatic hydrocarbons: linking electronic and molecular structure

Trends linking topology of PAH to their electronic properties are reported, evaluating how HOMO–LUMO gap depends on structure and size.

Identification and quantification of seven fused aromatic rings C26H14 peri-condensed benzenoid polycyclic aromatic hydrocarbons in a complex mixture of polycyclic aromatic hydrocarbons from coal tar

A methodology for the characterization of groups of polycyclic aromatic hydrocarbons (PAHs) using a combination of normal phase liquid chromatography with ultraviolet-visible spectroscopy (NPLC/UV-vis) and gas chromatography with mass spectrometry (GC/MS) was used for the identification and quantification of seven fused aromatic rings C26H14 peri-condensed benzenoid polycyclic aromatic hydrocarbons, PAHs, in standard reference material (SRM) 1597a, complex mixture of PAHs from coal tar. The NPLC/UV-vis isolated the fractions based on the number of aromatic carbons and the GC/MS allowed the identification and quantification of five of the nine C26H14 PAH isomers; naphtho[1,2,3,4-ghi]perylene, dibenzo[b,ghi]perylene, dibenzo[b,pqr]perylene, naphtho[8,1,2-bcd]perylene, and dibenzo[cd,lm]perylene using a retention time comparison with authentic reference standards. For the other four benzenoid isomers with no available reference standards the following two approaches were used. First, the annellation theory was used to achieve the potential identification of benzo[qr]naphtho[3,2,1,8-defg]chrysene, and second, the elution distribution in the GC fractions was used to support the potential identification of benzo[qr]naphtho[3,2,1,8-defg]chrysene and to reach the tentative identifications of dibenzo[a,ghi]perylene, naphtho[7,8,1,2,3-pqrst]pentaphene, and anthra[2,1,9,8-opqra]naphthacene. It is the first time that naphtho[1,2,3,4-ghi]perylene, dibenzo[b,ghi]perylene, dibenzo[b,pqr]perylene, naphtho[8,1,2-bcd]perylene, and dibenzo[cd,lm]perylene are quantified, and the first time that benzo[qr]naphtho[3,2,1,8-defg]chrysene is potentially identified, in any sample, in any context.

Molecular asphaltene models based on Clar sextet theory

Asphaltene isomers proposed using Clar sextet theory. the new arrangement of aromatic rings optimizes the location of pi-sextets.