Representation of molecules by atomic charges: A new population analysis

For the calculation of atomic charges in molecules, a new fast procedure based on extended Mulliken population analysis is presented. The reliability of the new population analysis is tested within the AM1 approximation and the results are compared in detail with those obtained by different methods reported in the literature.     

Crystal structure of rosmanol-9-ethylether

The title compound: 2H-10,4a-(epoxy-methano)-phenantren-12-one-1,3,4,9,10,10a-hexahydro-5,6-dihydroxy-9-etoxy-1,1-dirnethyl-7-(1-methylethyl), was isolated fromSalvia officinalis L. andHyssopus officinalis L. C₂₂H₃₀O₅, orthorhombic, P2₁2₁2₁, (No. 19)a=8.309(1),b=11.320(2),c=22.060(3) Å,V=2075.0(9) ų,Z=4,D _x=1.199 g·cm^–3, (CuK)=1.54184 Å,=6.43 cm^–1, F(000)=808,T=296(1) K. The structure was solved by direct methods and refined toR=0.047 for 1824 observed reflections collected on a CAD-4 diffractometer. In the course of structure refinement conformational disorder of the isopropyl moiety and the terminal methyl group pertaining to the ethoxy ligand was established. They result altogether in four different conformers.Alternatively it can be termed 9-ethoxyrosmanol.     

Semispectroscopic and quantitative structure-property relationship estimates of the equilibrium and vibrationally averaged structure and dipole moment of 1-buten-3-yne

Systematic quantum chemical calculations have been performed to obtain precise estimates of the equilibrium and vibrationally averaged molecular structure and electric dipole moment of vinylacetylene (VA, 1-buten-3-yne). Anharmonic (cubic and semi-diagonal quartic) MP2/cc-pVTZ force fields in normal coordinates were computed to account for anharmonic vibrational effects, including zero-point contributions to the rotational constants and the electric dipole moment. A simultaneous weighted least-squares structural refinement was performed, resulting in the best semispectroscopic estimate of the re structure of VA. The refinement was based on experimentally measured ground-state rotational constants of two isotopologs of VA corrected to equilibrium values using MP2/cc-pVTZ vibration-rotation interaction constants and all-electron CCSD(T)/aug-cc-pVTZ structural constraints. The semispectroscopic re structure of VA agrees excellently with the high-level CCSD(T)/aug-cc-pVTZ ab initio structure. The most dependable, CCSD(T)/cc-pVQZ//CCSD(T)/aug-cc-pVTZ equilibrium electric dipole moment of VA, in D, is mua= 0.4088, mub= 0.0004, and muc= 0. The vibrationally corrected a-component of 0.4214 D is in excellent agreement with one of the available experimental values. The present analysis shows that mub is negligible even after vibrational correction. A simple quantitative structure-property relationship (QSPR) model resulted in a highly similar estimate, 0.45 D, for the electric dipole moment of VA.     

Complexation of nitrostyrenes with soluble β-cyclodextrin polymer studied by reversed-phase thin-layer chromatography

Cyclodextrin complexation decreases the apparent lipophilicity of hydrophobic guest molecules. A higher complex stability results in a larger decrease of lipophilicity as determined by reversed-phase thin-layer chromatography. The method was applied to study the complex formation of 33 nitrostyrene derivatives with a water soluble cross linked -cyclodextrin polymer (weight average molecular weight: 4300). The substituents in thepara position of the benzene ring had a higher impact on the complex stability than those in themeta andortho positions. The substituents on the alkyl side chain influenced the complex stability to the same extent as those on the benzen ring.     

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Versatile synthesis of oxindole-1,3-dicarboxamides

A new, high-yielding synthesis of oxindole-1,3-dicarboxamides was elaborated starting from 1-phenoxycarbonyl-3-ethoxycarbonyl-2-oxindole and 1,3-diphenoxycarbonyl-2-oxindole. This method permits also the preparation of N,N,N′-tri- and N,N,N′,N′-tetrasubstituted oxidole-1,3-dicarboxamides, families of compounds that are unknown in the literature. The scope and limitations of the methodology have also been investigated, and a remarkable selectivity has been observed among the amines used in the amidation steps.     

Confirmation of the Absolute (3R,3′S,6′R)‐Configuration of (all‐E)‐3′‐Epilutein

Circular dichroism (CD) spectroscopy was used to distinguish between the isomeric (all‐E)‐configured 3′‐epilutein ( 2 ) and 6′‐epilutein ( 8 ) to establish the absolute configuration of epilutein samples of different (natural and semisynthetic) origin, including samples of 2 obtained from thermally processed sorrel. Thus, the CD data of lutein ( 1 ) and epilutein samples ( 2 ) were compared. Our results unambiguously confirmed the (3R,3′S,6′R)‐configuration of all epilutein samples. Compound 2 was thoroughly characterized, and its ¹³C‐NMR data are published herewith for the first time.     

Reaction of benzylidenebenzocyclanones with dithiocarbamic acid and thiourea

Summary Reaction of 2-benzylidene-1-benzocyclanones1 with dithiocarbamic acid afforded open-chain addition products2A–4B. Dehydration of the adducts yielded tricyclic 1,3-thiazine-2-thiones5 and6. Treatment of1 with thiourea under acid conditions gave tricyclic 2-amino-1,3-thiazines7–9. IR and¹H NMR spectroscopic investigations showed7–9 to exist predominantly in the amino tautomeric form both in the solid state and in solution.

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Die Umsetzung von 2-Benzyliden-benzocyclanonen mit Dithiocarbaminsäure und Thioharnstoff

Zusammenfassung Die Reaktionen der 2-Benzyliden-1-benzocyclanone1 mit Dithiocarbaminsäure liefern kettenförmige Additionsprodukte2A–4B. Die Dehydratisierung der Additionsprodukte führt zu tricyklischen 1,3-Thiazin-2-thionen5 und6. Durch Behandlung von1 mit Thioharnstoff unter sauren Bedingungen wurden tricyclische 2-Amino-1,3-Thiazine7–9 gebildet. IR- und¹H-NMR-spektroskopische Untersuchungen zeigten, dass7–9 sowohl in Substanz als auch in Lösungen überwiegend in der amino-tautomeren Form existieren.

     

Chemistry of an Unexplored Heterocyclic Ring System: Versatile Synthesis of 5‐Aryl‐2,3,4‐benzothiadiazepine 2,2‐dioxides

The article gives insight into the synthetic approach of a practically new heterocyclic ring system, 2,3,4‐benzothiadiazepines. Starting from the easily available phthalides, an efficient synthesis of 5‐aryl‐2,3,4‐benzothiadiazepine 2,2‐dioxides is described here. Owing to their close structural similarity to 2,3‐benzodiazepines and 2,3‐benzodiazepine‐4‐ones, two well‐known bioactive compound families, the new derivatives can be of importance in medicinal chemistry.     

Equilibrium and formation/dissociation kinetics of some Ln(III)PCTA complexes

The protonation constants () of 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (PCTA) and stability constants of complexes formed between this pyridine-containing macrocycle and several different metal ions have been determined in 1.0 M KCl at 25 degrees C and compared to previous literature values. The first protonation constant was found to be 0.5-0.6 log units higher than the value reported previously, and a total of five protonation steps were detected (log = 11.36, 7.35, 3.83, 2.12, and 1.29). The stability constants of complexes formed between PCTA and Mg2+, Ca2+, Cu2+, and Zn2+ were also somewhat higher than those previously reported, but this difference could be largely attributed to the higher first protonation constant of the ligand. Stability constants of complexes formed between PCTA and the Ln3+ series of ions and Y3+ were determined by using an "out-of-cell" potentiometric method. These values ranged from log K = 18.15 for Ce(PCTA) to log K = 20.63 for Yb(PCTA), increasing along the Ln series in proportion to decreasing Ln3+ cation size. The rates of complex formation for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA) were followed by conventional UV-vis spectroscopy in the pH range 3.5-4.4. First-order rate constants (saturation kinetics) obtained for different ligand-to-metal ion ratios were consistent with the rapid formation of a diprotonated intermediate, Ln(H(2)PCTA)(2+). The stabilities of the intermediates as determined from the kinetic data were 2.81, 3.12, 2.97, and 2.69 log K units for Ce(H(2)PCTA), Eu(H(2)PCTA), Y(H(2)PCTA), and Yb(H(2)PCTA), respectively. Rearrangement of these intermediates to the fully chelated complexes was the rate-determining step, and the rate constant (k(r)) for this process was found to be inversely proportional to the proton concentration. The formation rates (k(OH)) increased with a decrease in the lanthanide ion size [9.68 x 10(7), 1.74 x 10(8), 1.13 x 10(8), and 1.11 x 10(9) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively]. These data indicate that the Ln(PCTA) complexes exhibit the fastest formation rates among all lanthanide macrocyclic ligand complexes studied to date. The acid-catalyzed dissociation rates (k1) varied with the cation from 9.61 x 10(-4), 5.08 x 10(-4), 1.07 x 10(-3), and 2.80 x 10(-4) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively.