Integrated multispectroscopic and DFT analysis of molecular heterogeneity in Garabagh asphaltenes (Azerbaijan)

This study presents the first systematic analysis of the molecular architecture of asphaltenes isolated from Garabagh petroleum (Azerbaijan) by integrating multi-spectroscopic experimental methods with quantum-chemical modeling. Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) results reveal a heteroatom-rich (O + N + S = 22.2%), highly functionalized (CO, SO, NH), moderately aromatic (f_ar = 0.478), and highly substituted (Σ = 0.54) structural framework. High-resolution mass spectrometry (HRMS) indicates a broad molecular weight distribution within the 145-800 Da range and confirms the presence of 4-6 fused aromatic-naphthenic fragments. X-ray diffraction (XRD) confirms an amorphous structure with coexisting aliphatic/aromatic domains and no crystalline order. Shows strong 300-600 nm absorbance, indicating pronounced π-π^⁎ interactions. Thermogravimetric and differential thermogravimetric (TG/DTG) analyses show thermal stability up to 296 °C, decomposition in the 463-500 °C range, and 39.49% coke residue, which may be related to the presence of condensed aromatic nuclei. Density functional theory (DFT) optimized structural archetypes yield fragment-dependent HOMO-LUMO gaps (1.689-3.227 eV) and intramolecular H···O distances (1.647-1.693 Å). Hard fractions (η ≈ 1.614 eV) govern intrinsic chemical stability, while soft electrophilic isomers (σ ≈ 0.592 eV^-1) exhibit enhanced reactive propensities. Collectively, the cross-validated results define an archipelago-dominant architecture, offering a unified molecular-level framework for interpreting the intrinsic electronic properties and molecular heterogeneity of asphaltenes.