The proposition of the hypothesis-relating structure with properties of asphaltenes is a very important endeavor. In view of their complexity, being an intricate mixture of high-molecular-mass compounds, experimental and theoretical procedures must be designed to check whether the structures proposed are consistent with expected and found behavior. During recent years, a structural characteristic of asphaltene, whereby the several polycyclic systems present in them are joined by flexible aliphatic chains, has been proposed by several authors. For simplicity, we will refer to this as the rosary-type structure. In this paper, using both reported as well as new experimental and theoretical results, an attempt is made to show how asphaltene properties, such as molecular-mass distribution, molecular fragmentation, solubility, adsorption, trapping of molecules, solvent swelling, and aging, could be accounted for in terms of the above rosary-type structures.

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A sample of asphaltenes (ACN) precipitated from Cerro Negro crude oil had been divided into 14 fractions using a dialysis procedure employing THF-acetone mixtures as the extracting solvent. Seven extracts (F 1 -F 7 ) and the corresponding residues R 1 -R 7 were obtained as the mixture composition changed from 40 to 100% THF. These materials were characterized by elemental analyses, VPO, solubility, C-13 NMR, and electron paramagnetic resonance (EPR). As the last fractions are aproached, the following trends were observed: H/C decreases, aromaticity increases, solubility descreases, and S d , the spin density, increases. Removal of the first fraction (F 1 , 15% of ACN, acetone-THF (40%)) afforded a residue (R 1 ) insoluble in toluene, indicating that 85% of ACN is present as colloidal particles (R 1 ) dispersed in this solvent by F 1 . More than 12% of ACN found in the last residues (R 6 and R 7 ) were found to be insoluble in organic solvents, suggesting that these fractions are formed by aggregates of molecules held in place by strong intermolecular forces. In an asphaltene micelle they would be at the core and its solubility in organic solvents is due to dispersion by the other components of the micelle. Althought other effects are not disregarded, it is suggested that transannular electron delocalization in free radicals could play an important role in aggregate formation.

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Two acidic samples, A and B, were isolated from Cerro Negro extraheavy crude oil. Sample A has a relatively low number average molecular weight (M n = 480 Da), low aromaticity (f a = 15.2%), and low γ (6.8 m Nm-1, toluene−0.1 N HCl), whereas for B, these values were M n = 1200 Da, f a = 20%, and γ = 14.8 m Nm-1. These values could be compared to those for Cerro Negro asphaltenes under the same conditions (M n = 5000, in toluene by VPO, f a = 47%, γ = 20.9 m Nm-1).

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