Synthesis and crystal structure of racemic (R*,R*)-2,2′-(1,4-phenylene)bis(3-phenyl-2,3,5,6-tetrahydro-4H-1,3-thiazin-4-one)

In the racemic title compound, C26H24N2O2S2, one of the thiazine rings shows a twisted boat conformation (Q = 0.743 Å, θ = 92.1°) and the other a half-chair puckering (Q = 0.669 Å, θ = 54.3°). The terminal phenyl rings are almost parallel to each other [dihedral angle 21.71 (10)°]. Both of these rings are orthogonal to the central phenyl ring, subtending a dihedral angle of about 78° in each case. The extended structure is consolidated by C—H...O and C—H...S hydrogen bonds as well as aromatic ring interactions of parallel-displaced and T-type. The molecule has approximate C2 local symmetry but this is not carried over to its three-dimensional structure or the intermolecular interactions.

Crystal structures of two solvated 2-aryl-3-phenyl-2,3-dihydro-4H-pyrido[3,2-e][1,3]thiazin-4-ones

The synthesis and crystal structures of 2-(4-fluorophenyl)-3-phenyl-2,3-dihydro-4H-pyrido[3,2-e][1,3]thiazin-4-one toluene hemisolvate (1), C19H13FN2OS·0.5C7H8, and 2-(4-nitrophenyl)-3-phenyl-2,3-dihydro-4H-pyrido[3,2-e][1,3]thiazin-4-one isopropanol 0.25-solvate 0.0625-hydrate (2), C19H13N3O3S·0.25C3H7O·0.0625H2O, are reported. Both are racemic mixtures (centrosymmetric crystal structures) of the individual compounds and incorporate solvent molecules in their structures. Compound 2 has four thiazine molecules in the asymmetric unit. All the thiazine rings in this study show an envelope pucker, with the C atom bearing the substituted phenyl ring displaced from the other atoms. The phenyl and aryl rings in each of the molecules are roughly orthogonal to each other, with dihedral angles of about 75°. The extended structures of 1 and 2 are consolidated by C—H...O and C—H...N(π), as well as T-type (C—H...π) interactions. Parallel aromatic ring interactions (π–π stacking) are observed only in 2.

Crystal structure of diethyl 2-acetoxy-2-[3-(4-nitrophenyl)-3-oxo-1-phenylpropyl]malonate

In the racemic title compound, C24H25NO9, the dihedral angle between the planes of the two benzene-ring systems is 80.16 (6)°, while the side-chain conformation is stabilized by a methylene–carboxyl C—H...O hydrogen bond. Weak intermolecular C—H...O hydrogen bonds form inversion dimers [graph setR22(16)] which are linked into chains extending alonga. Further C—H...O hydrogen bonding extends the structure alongbthrough cyclicR22(10) motifs. Although no π–π aromatic ring interactions are present in the structure, C—H...π ring interactions acrosscgenerate an overall three-dimensional supramolecular structure.

2,3-Diphenyl-2,3-dihydro-4H-pyrido[3,2-e][1,3]thiazin-4-one

In the racemic title compound, C19H14N2OS, the two phenyl substituents on the 1,3-thiazine ring are almost perpendicular to the pyridine ring which is fused to the thiazine ring [inter-ring dihedral angles = 87.90 (8) and 85.54 (7)°]. The dihedral angle between the two phenyl rings is 75.11 (7)°. The six-membered thiazine ring has an envelope conformation with theortho-related C atom forming the flap. The crystals exhibit face-to-edge aromatic-ring interactions with the nearest C—H...C distance equal to 3.676 (3) Å.

Charge vs. Porosity - Some Influences on the Adsorption of Natural Organic Matter (NOM) by Activated Carbon

The adsorption of NOM ultrafiltration fractions onto ten activated carbons was studied. The aim of the research was the clarification of the effects of carbon charge and pore volume distribution and NOM charge and molecular weight on adsorption. The effect of pH and ionic strength on adsorption mechanisms was determined, and it was found that, in the absence of strong electrostatic effects, adsorption occurred by a pore filling mechanism in which the available pore volume was filled. At neutral pH the NOM has a significant negative charge which can affect the adsorption in several ways. At low surface concentrations on activated carbon with positive surface groups there is direct surface-NOM electrostatic attraction (screening reduced adsorption). At higher surface concentrations the adsorption becomes predominantly a physical surface-NOM attraction, possibly due to hydrophobic or aromatic ring interactions. The electrostatic effects are mainly caused by the lateral repulsion of the NOM that prevents the close-packed arrangement apparent at pH 3 (screening enhanced adsorption). For one activated carbon it was shown that the degree of ionisation of the adsorbed NOM is strongly dependent on the surface concentration.