Adama Saba

Revisiting the photophysical properties and excited singlet-state dipole moments of several coumarin derivatives

The solvent effects on the electronic absorption and fluorescence emission spectra of several coumarins derivatives, containing amino, N,N-dimethyl-amino, N,N-diethyl-amino, hydroxyl, methyl, carboxyl, or halogen substituents at the positions 7, 4, or 3, were investigated in eight solvents with various polarities. The first excited singlet-state dipole moments of these coumarins were determined by various solvatochromic methods, using the theoretical ground-state dipole moments which were calculated by the AM1 method. The first excited singlet-state dipole moment values were obtained by the Bakhshiev, Kawski-Chamma-Viallet, Lippert-Mataga, and Reichardt-Dimroth equations, and were compared to the ground-state dipole moments. In all cases, the dipole moments were found to be higher in the excited singlet-state than in the ground state because of the different electron densities in both states. The red-shifts of the absorption and fluorescence emission bands, observed for most compounds upon increasing the solvent polarity, indicated that the electronic transitions were of π-π* nature.

Mass Spectrometry Study of Coumarins: Correlation Between Charges of Atoms and Fragmentation Processes

ABSTRACT The mass spectrometry of a number of 6-substituted coumarins was studied in the context of correlating fragmentation pathways and electronic charges of atoms performed by AM1 semiempirical method. The atomic charges of atoms are found to be good predictors of the fragmentation pathways.

2-Oxo-2H-chromen-4-yl 4-methyl­benzoate

The asymmetric unit of the title compound, C17H12O4, consists of two independent molecules. The chromen-2-one ring and the 4-methylbenzoate side chain are inclined to one another at a dihedral angle of 64.79 (10)° in one molecule and 88.3 (1)° in the other. In the crystal, molecules form R 2 2(8) centrosymmetric dimers via C—H⋯O hydrogen bonds. These dimers are stacked by C—H⋯O hydrogen bonds, resulting in R 2 2(18) and R 3 2(16) ring motifs. π–π stacking interactions between two parallel chromen-2-one rings, with centroid–centroid distances of 3.743 (1) and 3.771 (1) Å, are also present.

Crystal structure of 2-oxo-2H-chromen-3-yl propano­ate

In the title compound, C12H9O4, the dihedral angle between the coumarin ring system and the propionate side chain is 78.48 (8)°.

2-Oxo-2H-chromen-4-yl 4-tert-butyl-benzoate.

In the title molecule, C20H18O4, the three methyl groups of the tert-butyl substituent show rotational disorder. Each methyl group is split over three positions, with refined site-occupation factors of 0.711 (4), 0.146 (3) and 0.144 (4). The benzene ring of the benzoate group is oriented at a dihedral angle of 60.70 (7)° with respect to the planar chromene ring [maximum deviation = 0.046 (2) Å]. The crystal structure features centrosymmetric R 2 2(8) dimers formed via C—H⋯O interactions, and these dimeric aggregates are connected by C—H⋯π interactions.

2-Oxochromen-4-yl 4-(dimethyl­amino)­benzoate

In the title molecule, C18H15NO4, the benzoate ring is oriented at a dihedral angle of 43.43 (6)° with respect to the planar [maximum deviation = 0.038 (2) Å] chromene ring. The crystal structure features R 2 2(12) centrosymetric dimers formed via C—H⋯O interactions and these dimeric aggregates are connected by C—H⋯π interactions.

Dérives substitués de la ferrophtalocyanine

Abstract Iron(II) phthalocyanine (PcFe II ) complexes substituted on the peripheral carbons (CH 3 ) 8 PcFe II , Cl 16 PcFe II , Br 16 PcFe II , (COONa) 4 PcFe II and their derivatives with axial pyridines (PyR; R = H, CH 3 , CH 2 OH, CHO, Cl, OH, CN) have been prepared and characterized by optical and vibrational spectroscopy. The charge-transfer transitions between the Π levels of the axial ligands and the Π * levels of the phthalocyanine are confirmed. IR absorptions are assigned in the new series of derivatives. The CT electronic absorption band maxima are correlated with the FeN 4 vibrations of the central skeleton of the complexes.

NMR and AM1 Study of the Tautomeric Equilibrium of Isochroman-1,2-diones

Abstract Reaction of homophtalic anhydrid with aliphatic or aryl anhydrids (or acid chlorides) and an appropriate base gives 4-acyl and 4-aroylisochroman-1,3-diones. The structure of these isochroman-1,3-diones was determined by 1H, 13C and 17O NMR spectrometry. In solution, among the three possible tautomers, only the enolic one with exocyclic double bond was observed. These results are in good agreements with AMI calculations ones.

Isocoumarines: Structural Study by NMR and by AM1 Semi-Empirical Method

Abstract Study of a serie of isocoumarins by 13C and 17O NMR spectrometry and AM1 method is reported. These methods gave valuable informations on electronic effect and the structure of isocoumarins.

17O and 13C NMR Studies of Isobenzopyrylium Salts

Abstract 13C and 17O NMR chemical shifts for a series of isobenzopyrylium salts are reported. The oxygen signal range from 300 to 270 ppm as a double bonded carboxylic oxygen, From the 17O and 13C data valuable informations on the conjugative and substituent effects of isobenzopyrylium salts were obtained.