A new class of flexible energetic salts. Part 7: The structures of the guanidinium and hydroxyguanidinium salts of dinitramide

The crystal structures of two amine base salts of dinitramide, the guanidinium 1, and the hydroxyguanidinium 2, have been determined. 1 crystallizes in the triclinic space group with cell dimensions a = 8.325(2) Å, b = 9.301 (2) Å, c = 9.868(2) Å, = 84.73(3)°, = 69.25(3)°, = 67.55(3)°, while 2 crystallizes in the noncentric monoclinic space group Pc with cell dimensions a = 7.098 (2) Å, b = 3.5160 (10) Å, c = 14.358(3) Å, = 98.940(10)°. The structures of 1 and 2 contain protonated amine cations and dinitramide anions linked by hydrogen bonding. In both structures the conformations adopted by the dinitramine anions can be related to the types of hydrogen bonds it forms with the surrounding amine cations.     

The crystal and molecular structures of highly substituted cubanes: 1,2,4,7-tetra(carboxymethyl)cubane and 1,2,3,5,7-penta(carboxymethyl)cubane

The structures of the title compounds, 1,2,4,7-tetra(carboxymethyl)cubane 1 and 1,2,3,5,7-penta(carboxymethyl)cubane2, have been determined.1 crystallized in the space group with cell dimensionsa=6.098(2),b=10.686(2),c=13.459(2) Å, =69.82(1), =77.01(1), =74.00(1)°, while2 crystallized in the monoclinic space group P2₁/c with cell dimensionsa=15.139(2),b=12.775(1),c=9.849(2) Å, =107.01(1)°. These molecules were derived from their parent carboxylic acids by esterification with methanol. They are unusual for several reasons. The first is that they both contain substituents on adjacent carbon atoms in the cubane framework. There are only a few reports in the literature of this type of cubane structure. The second molecule is unique in that it has five substituents attached to a cubane moiety. This is the one of the few cubane derivatives with more than four substituents to be structurally characterized and results in a cubane molecule in which there are three faces with three substituents and three faces with only two substituents.     

Structural and spectral studies of binuclear copper(II) 2-acetylpyridine 3-azacyclothiosemicarbazones with sulfato bridges

Structures of two binuclear copper(II) complexes with sulfato bridges and tridentate 2-acetylpyridine 3-azacyclothiosemicarbazone ligands have been solved. The complex-sulfato-bis{(2-acetylpyridine 3-hexamethyleneiminyl-thiosemicarbazonato)copper(II)} N,N-dimethylformamide, [Cu(Achexim)]₂SO₄·DMF, has the following structural properties: triclinic, P1¯(#2), a = 12.314(4), b = 15.885(4), c = 10.959(4) Å, = 103.25(2), = 103.60(2), = 109.94(2)°, V = 1843(2) ų, and Z = 2; for -sulfato-bis{(2-acetylpyridine 3-piperidylthiosemicarbazonato)copper(II)}chloroform, [Cu(Acpip)]₂SO₄·CHCl₃: triclinic, P1¯(#2), a = 11.657(1), b = 17.101(2), c = 10.338(1) Å, = 98.51(1), = 109.294(7), = 107.016(9)°, V = 1790.3(4) ų, and Z = 2. The size of the azacyclo ring significantly affects the stereochemistry of these binuclear complexes.     

Glass transition and fragility of Na2O-TeO2 glasses

The heat capacity (C_p) change in the glass transition region for the xNa₂O ·(100−x)TeO₂, mol%, glass forming melts with x=7.5, 11.1, 15.0, 20.0 and 25.0 was measured as a function of heating rate (2, 4, 6, 10 and 15 °C/min) using differential scanning calorimetry. The glass transition properties that have been measured and reported in this paper include the glass transition temperature (T_g), glass transition width (ΔT_g), heat capacities in the glassy and liquid state (C_pg and C_pl) and the activation enthalpy for glass transition (). T_g for these sodium tellurite melts decreased and increased with increasing Na₂O. Values of the ratio C_pl/C_pg ranged between 1.28 and 2.47, and the fragility parameter ranged between 100 and 130, suggesting that these glass forming melts may be classified as intermediate between typical strong and fragile liquids. The viscosity, η, calculated at a few selected temperatures near the glass transition region decreased with increasing Na₂O at any given temperature, which is also expected.     

Crystal structure of N-(4-nitrophenyl)-N-phenylsulfonamide

The crystal structure of N-(4-nitrophenyl)-N-phenylsulfonamide (C₁₈H₁₄N₂O₄S), a derivative of sulfonamide, has been determined by X-ray diffraction method using CuK radiation. The compound crystallizes in the monoclinic space groupP2₁/n, witha=24.463(1),b=5.745(2),c=11.428(3)Å and=94.39(2)°. The structure was solved by direct methods and refined by full-matrix least squares to a finalR value of 0.045 with 3032 unique reflections. The dihedral angle between the substituents phenyl ring B and the phenyl A is 94.7(3)°. The S atom is in the usual distorted tetrahedral configuration.     

Dispersion polymerization of acrylamide: Part II. 2,2′‐Azobisisobutyronitrile initiator

Dispersion polymerization of acrylamide in tert‐butyl alcohol (TBA)‐water media (TBA ⩾ 50 vol %) using poly(vinyl methyl ether) (PVME) as the stabilizer and 2,2′‐azobisisobutyronitrile (AIBN) as the initiator at 50°C has been studied. The conversion‐time curve shows autoacceleration taking place from the very early stage of the reaction (measured from 4% conversion level). Molecular weight increases with conversion indicating that the gel effect is operative. This suggests that a major part (if not the whole) of the polymerization occurs in the particle phase. The effects of the concentrations of the stabilizer, the initiator, the monomer, and the solvent composition on particle size have been explained on the basis of particle phase polymerization. The feeding of the particles by the monomer presumably occurs through the solvent channels of the swollen particles. The swelling data of polyacrylamide films in various TBA‐water mixtures are given. The similarity and differences between the AIBN and ammonium persulfate (APS) initiated systems (published earlier by us) have been discussed. In general, particles are more polydisperse and bigger in the former case than in the latter. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 493–499, 1999     

Parallel finite element computation of missile aerodynamics

A flow simulation tool, developed by the authors at the Army HPC Research Center, for compressible flows governed by the Navier–Stokes equations is used to study missile aerodynamics at supersonic speeds, high angles of attack and for large Reynolds numbers. The goal of this study is the evaluation of this Navier–Stokes computational technique for the prediction of separated flow fields around high-length-to-diameter (L/D) bodies. In particular, this paper addresses two issues: (i) turbulence modelling with a finite element computational technique and (ii) efficient performance of the computational technique on two different multiprocessor mainframes, the Thinking Machines CM-5 and CRAY T3D. The paper first provides a discussion of the Navier–Stokes computational technique and the algorithm issues for achieving efficient performance on the CM-5 and T3D. Next, comparisons are shown between the computation and experiment for supersonic ramp flow to evaluate the suitability of the turbulence model. Following that, results of the computations for missile flow fields are shown for laminar and turbulent viscous effects. © 1997 John Wiley & Sons, Ltd.     

Applications of triple resonance NMR techniques to the study of polymer structure and reactivity

The utility of isotopic labeling combined with triple resonance nuclear magnetic resonance (NMR) techniques for polymer structure and reactivity investigations will be demonstrated. One dimensional (1D) and two dimensional (2D) ¹H/¹⁹F/¹³C triple resonance NMR experiments have been used to study the structure of fluoropolymers; and ¹H/²H/¹³C triple resonance techniques have been used to study the reactivity of poly[(styrene-alt-(methyl methacrylate)] and the structure of deuterated polybutadiene. These methods provide a unique ability to selectively detect resonances of structural features that are present in minute amounts in polymers, without interference from the much larger signals of the rest of the polymer.     

Origin of product ions in the MS/MS spectra of peptides in a quadrupole ion trap

Stored waveform inverse Fourier transform and double resonance techniques have been used in conjunction with a quadrupole ion trap to study the dissociation patterns of peptide ions. These experiments provide insight into the origin of individual product ions in an MS/MS spectrum. Results show for a series of leucine enkephalin analogues with five amino acid residues that the b ₄ ion is the main product ion through which many other product ions arise. It was also observed that the percentage of the a ₄ product ions that are formed directly from the protonated molecule (M+H)⁺ depends on the nature of the fourth amino acid residue. In addition, it was determined that in the peptides studied here lower series b ions (e.g., b ₃ arise from direct dissociation of higher series b ions (e.g., b ₄ only about 50% of the time.