Asphaltene aggregation mechanism is still a nebulous and controversial issue. Many authors argue that the aggregation of its components is due to π-stacking interactions, nonetheless, alkyl chains, heteroatoms, and even acidic groups are also constituents of asphaltenes and can play an important role in the chemistry of asphaltene. Excimers from pyrene are easily detected by fluorescence and were used in the current study to probe the effect of the side chain on the π-stacking capacity of pyrene. Pyrene was acylated with acyl chains varying from two to twelve carbon atoms, and the effect of the variation of the acyl chain length on excimer formation was followed by fluorescence emission spectroscopy. The results revealed that as the side chain grows from two to twelve carbon atoms the excimer/monomer ratio decreases and the excimer heat of formation drops from ΔH = -6.00 to -1.29 kcal mol-1. Further, the crystal structure of octanoyl pyrene (PC8) indicates that in the crystal structure, the aromatic moiety faces the acyl chain. This result was corroborated by density functional theory (DFT) calculations. Finally, the results were compared with two different asphaltenes and indicate that π-stacking cannot be assumed as the main driving force for asphaltene aggregation. issue πstacking π stacking interactions nonetheless heteroatoms spectroscopy excimermonomer monomer 6.00 600 6 00 -6.0 1.29 129 1 29 -1.2 mol1. mol1 mol 1. mol-1 Further PC8 PC (PC8 DFT (DFT calculations Finally 6.0 60 0 -6. 1.2 12 2 -1. mol- (PC 6. -6 -1 -

A reação de tert-butil 2-(3-cloro-1,4-dioxo-1,4-di-hidronaftalen-2-ilamino)etilcarbamato com CF3COOH/CH2Cl2 fornece 5-cloro-3,4-di-hidrobenzo[f]quinoxalin-6(2H)-ona. Este composto sofre desidrogenação promovida por ácido na presença de água para dar a 5-clorobenzo[f]quinoxalin-6-ol, inédita. A estrutura molecular no estado sólido, determinada por um estudo de difração de raios X (XRD), e os dados em solução confirmam que a benzoquinoxalina existe na forma do tautômero enol-imina, tanto no estado sólido, quanto em solução, diferentemente de 5-cloro-3,4-di-hidrobenzo[f]quinoxalin-6(2H)-ona que exibe o arranjo ceto-amino. Cálculos de teoria do funcional da densidade (DFT) confirmam a preferência da benzoquinoxalina e dos compostos análogos contendo grupos H ou CH3 no lugar do Cl pela forma enol-imina. Sugere-se que a preferência da benzoquinoxalina pela estrutura enol-imina se deva ao maior caráter aromático desta estrutura em comparação com a forma ceto-amina. Os cálculos DFT dos dois tautômeros das benzo[a]fenazin-5(7H)-onas análogas às benzo[f]quinoxalin-6(4H)-onas indicaram que as estabilidades relativas são dominadas por efeitos de solvatação, no primeiro caso, e pelo grau de aromaticidade no segundo.

The reaction of tert-butyl 2-(3-chloro-1,4-dioxo-1,4-dihydronaphthalen-2-ylamino) ethylcarbamate with CF3COOH/CH2Cl2 yields 5-chloro-3,4-dihydrobenzo[f]quinoxalin6(2H)-one which undergoes acid-promoted dehydrogenation in the presence of water to give novel 5-chlorobenzo[f]quinoxalin-6-ol. The molecular structure of 5-chlorobenzo[f]quinoxalin6-ol in the solid state, determined by an X-ray diffraction (XRD) study, and the solution data confirm that it exists as the enol-imine tautomer, both in the solid state and in solution, differently from 5-chloro-3,4-dihydrobenzo[f]quinoxalin-6(2H)-one, which exhibits the keto-amine arrangement. Density functional theory (DFT) calculations confirmed the preference of 5-chlorobenzo[f]quinoxalin-6-ol and of the derivatives containing H and CH3 groups in place of the Cl atom for the enol-imine tautomer. It is suggested that the enol-imine structure is preferred for 5-chlorobenzo[f]quinoxalin-6-ol as a consequence of the higher aromatic character of this structure in comparison with the keto-amine form. DFT calculations carried out on the two tautomers of the benzo[a]phenazin-5(7H)-ones analogous to the benzo[f]quinoxalin-6(4H)-ones showed that the relative stabilities are dominated by solvation effects in the first case and the degree of aromaticity, in the latter.