Mittlere Schwingungsamplituden eines X2Y2-Molekülmodells mit C2h-Symmetrie: Anwendung auf dastrans-Difluordiazin

Zusammenfassung Es wurde eine Methode zur Berechnung der mittleren Schwingungsamplitudenquadrate für das Modell einesX ₂ Y ₂-Moleküls mit C_2h-Symmetrie unter Verwendung von Symmetriekoordinaten entwickelt und analytische Ausdrücke für die verschiedenen mittleren Amplitudenquadrat-Größen in Termen der symmetrisierten Matrizen der mittleren Amplitudenquadrate abgeleitet. Diese Methode wurde zur Bestimmung der mittleren Schwingungsamplituden sowohl der gebundenen wie auch der nicht gebundenen Atompaare destrans-Difluordiazins bei 298°K aus beobachteten Raman- und Infrarotgrundschwingungsfrequenzen und Angaben zur Molekülstruktur angewendet. Darüber hinaus wurden die molaren Größen der thermodynamischen Funktionen unter Annahme eines starren Rotator—harmonischen Oszillator-Modells für den Temperaturbereich 200 bis 2000°K berechnet. Die Ergebnisse der Berechnungen werden kurz diskutiert.

---

Mean amplitudes of vibration of an X₂Y₂ molecular model of C_2h-symmetry: Application to trans-difluorodiazine

A method for the determination of the mean-square amplitudes of vibration for anX ₂ Y ₂ molecular model with C_2h symmetry has been developed using the symmetry coordinates. Analytical expressions for the various mean-square amplitude quantities in terms of the symmetrized mean-square amplitude matrices have been derived. The method has been applied totrans-difluorodiazine for the determination of mean amplitudes of vibration for both bonded and nonbonded atom pairs at 298°K from the observed Raman and infrared fundamental frequencies and molecular structural data. In addition to these, molar thermodynamic functions have also been computed on the assumption of a rigid rotator, harmonic oscillator model for the temperature range 200–2000°K. A brief discussion of the results has been given.

     

Structure-reactivity correlation in bromate oscillatory systems in aqueous-acetonitrile mixed medium

The oscillatory behavior of eight substrates has been studied in the uncatalyzed and catalyzed [Mn(II) and ferroin] bromate systems in aqueous-acetonitrile mixed medium. The reactivities of structurally related compounds are correlated using their oscillatory characteristics. The exchange current density values of the redox couples involved play a vital role in deciding the oscillatory characteristics of the system.     

Synthesis and characterization of functional aliphatic copolyesters

Functional aliphatic copolyesters of succinic acid (SA) and citric acid (CA) were synthesized via direct copolycondensation in the presence of 1,4‐butanediol, with titanium(IV) butoxide as a catalyst. The effects of the comonomer and comonomer ratio on the polycondensation and the melting and glass‐transition temperatures were investigated. The melting temperature was very sensitive to the molar ratio of the SA–CA comonomer units. The chain extension of this poly(butylene succinate citrate) was carried out with hexamethylene diisocyanate. The intrinsic viscosity, crystallinity percentage, and rheological properties of these copolyesters were also studied. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3232–3239, 2002     

Carbon-13 fourier transform NMR studies of organotin compounds : III. Carbon-13 chemical shifts and tin-119—carbon-13 spin—spin coupling constants in acyclic,monocyclic and bicyclic organostannanes

Carbon-13 NMR parameters for 33 organotin compounds with a variety of structurul features were investigated in order to obtain information about the relationship between their structure and ¹³C NMR parameters. It was found that the substitution of a proton by a trialkyltin group generally produces an upfield shift for the directly bonded carbon. The γ-nuclei usually resonate at lower fields except where there is appreciable steric strain while the β-carbons undergo relatively constant shifts of approximately 3.5 to 4.5 ppm to lower fields. The magnitude of direct bond coupling Jz-sfnc;¹J(¹¹⁹Sn¹³C)z-sfnc; is influenced by the hybridization of the tin and the directly attached carbon atoms. In rigid organitins, the vicinal coupling constants show a Karplus type variation. In aliphatic organotins, the values of the vicinal¹¹⁹Sn¹³C coupling indicates a flexible molecular framework with a clear cut preference for certain conformations.     

Spectral signatures of the diffusional anomaly in water

Power spectra for various tagged particle quantities in bulk extended simple point charge model water [H. J. C. Berendsen, J. R. Grigera, and T. P. Straatsma, J. Phys. Chem. 91, 6269 (1987)] are shown to have a regime with 1f(alpha) dependence on frequency f with alpha lying between 1 and 1.5 if the dynamical changes in the particular observable are sensitive to the multiple time-scale behavior of the hydrogen-bond network. The variations in mobility associated with the diffusional anomaly are mirrored in the scaling exponent alpha associated with this multiple time-scale behavior, suggesting that monitoring of 1f(alpha) behavior is a simple and direct method for linking phenomena on three distinctive length and time scales: the local molecular environment, hydrogen-bond network reorganizations, and the diffusivity. Our results indicate that experimental studies of supercooled water to probe the density dependence of 1f(alpha) spectral features, or equivalent stretched exponential behavior in time-correlation functions, will be of interest.     

X-ray crystal structure analysis of nitroxazepine: 10-(3-dimethylaminopropyl)-2-nitro-10,11-dihydrodibenz [b,f][l,4]oxazepin-11-one

The title compound, C₁₈H₁₉O₄N₃,M _r=341, the base (I) of the dibenzoxazepine anti-depressant drug Sintamil, crystallizes in the orthorhombic space group,Pbca withZ=8 in a cella=8.636(2),b=23.687(3),c=16.787(3)Å,V _c=3434 ų. The structure was solved by direct methods and refined toR=0.102 (R _w=0.093) with 1348 observed CuK reflections. The tricyclic framework takes up a saddle shape with the heterocyclic ring in boat conformation; the flanking planar aromatic rings make angles 148.2(3), 150.8(3)° with the central ring plane, compared with 143.5(5), 158.1(5)° in Sintamil monohydrate (II). BothI andII have extended-CNMe₂ side chains (with appreciable thermal motion); this conformation, and the distances of the -N(CH₃)₃ nitrogen to the centers of aromatic rings (6.4 and 7.8 Å inI), are consistent with inhibition of uptake mechanisms underlying the pharmacological action.     

Modeling Biomass Gasification Using Thermodynamic Equilibrium Approach

In this paper, the thermodynamic equilibrium models for biomass gasification applicable to various gasifier types have been developed, with and without considering char. The equilibrium models were then modified closely matching the CH₄ only or both CH₄ and CO compositions from experimental data. It is shown that the modified model presented here based on thermodynamic equilibrium and taking into account local heat and mass considerations can be used to simulate the performance of a downdraft gasifier. The model can also be used to estimate the equilibrium composition of the syngas. Depending on the gasifier type and internal fluid flow, heat and mass transfer characteristics, with proper modification of the equilibrium model, a simple tool to simulate the operation and performance of varying types of biomass gasifier can be developed.     

A New Double Substrate Uncatalyzed Bromate Oscillator

A double substrate uncatalyzed bromate oscillator is reported. Oscillations occur for several minutes, the color of the solution alternating between dark brown and reddish yellow. The oscillatory wave form (Pt electrode) has a distinct pattern, with a progressive increase in the amplitude and time interval. The presence of both substrates namely 8-hydroxyquinoline and malonic acid is essential. This revised version was published online in June 2006 with corrections to the Cover Date.