Nowadays, 13C nuclear magnetic resonance (NMR) is used in the structural study of asphaltenes. However, the different carbon types in the polycyclic aromatic hydrocarbon (PAH) core of asphaltenes, to be able to establish their main backbone, have been reported to have different 13C NMR chemical shift ranges by different authors in the literature. Therefore, in the present study, the 13C NMR chemical shift ranges for the structural carbon types(a) Y-carbons (CY) or internal triple bridgehead aromatic carbons; (b) external peripheral aromatic carbon atoms at the junction of two fused rings, or external double bridgehead aromatic carbons (CAP3); (c) aromatic carbon atoms bonded to hydrogen atoms (CAH); and (d) carbon atoms bonded to heteroatoms (CAX) and carbon atoms bonded to hydrogen in the β position to a heteroatom (CAHβX)have been determined by combining calculated 13C NMR chemical shifts, at the gauge-independent atomic orbital-density functional theory level (GIAO-DFT), with measured experimental 13C NMR chemical shifts for PAHs that have been identified as being asphaltene-PAH cores and for PAHs that are not examples of asphaltene-PAH cores. The determined 13C NMR chemical shift ranges are reported.

The structural parameters and average molecular structures of the asphaltenes obtained from the Aguacate oilfield, located in the Golden Lane of Mexico, have been investigated combining experimental analysis and molecular simulation. The average molecular structural parameters of the polycyclic aromatic hydrocarbon (PAH) region, average number of fused aromatic rings (nFAR), average structural isomers in the polydispersity of the PAH core, average architecture, average molecular weight, and substituents in the PAH core have been determined by means of 13 C single-pulse excitation (SPE) nuclear magnetic resonance (NMR) in combination with 13 C distortionless enhancement by polarization transfer (DEPT)-135°experiments, 1 H NMR, X-ray photoelectron spectroscopy, fluorescence emission, and matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry. The total energy of the PAH isomers and their fluorescence emission are calculated with density functional theory and ZINDO/S, respectively. The PAH region structural parameters determined are (a) Y-carbons (C Y ) or internal triple bridgehead aromatic carbons, (b) external peripheral aromatic carbon atoms at the junction of two fused rings (C AP3 ), (c) aromatic carbon atoms bonded to hydrogen atoms (C AH ), (d) aromatic carbon atoms bonded to heteroatom (C AX ), (e) aromatic carbon atoms bonded to hydrogen at the β position with respect to the heteroatom (C AHβX ), and (f) substituted aromatic carbon atoms (C A-Caliph ). The 13 C NMR chemical shift ranges used for the different structural carbon atoms in the PAH core were obtained from our previous study [

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