Structure of 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine isethionate solvate (lamotrigine isethionate)

The crystal and molecular structure of lamotrigine isethionate, C₉H₈Cl₂N₅ ⁺ .HOC₂H₄SO₃ ^– has been determined by direct methods. The compound crystallizes in the tetragonal space group I4₁/a. The isethionate moiety forms multiple hydrogen bonds to the lamotrigine nucleus, three from one isethionate, two from a symmetry related isethionate and a further two from two different symmetry related molecules. Protonation of N(2) in the triazine ring, not observed in the native lamotrigine structure is presumably associated with the interaction of the isethionate moiety. Both rings in the lamotrigine moiety are essentially planar, with a dihedral angle of 66.08(7)° compared to 80.70° in native lamotrigine. The connecting bond length C(1)—C(6) = 1.493(3) Å also correlates well with values in related compounds (1.480(3) Å) in the native structures.     

The structure of 20 oximo-5α-pregnano-16-eno[3,4-C]-1′,2′,5′-oxadiazole (HS976)

The crystal and the molecular structure of the steroidal oxadiazole 20-oximo-5-pregnano-16-eno[3,4-C]-1,2,5-oxadiazole (C₂₁H₂₈N₂O₃) has been determined by direct methods, and refined to a finalR of 0.086 for 3100 observed reflections. The compound crystallizes in space groupP2₁, with cell dimensionsa=18.284(6),b=13.992(4),c=7.370(3)Å,=96.97(3)°;V=1885 ų,Z=4,D _x =1.27 g cm^–3, =1.5418 Å, (CuK =5.95 cm^–1. The two independent molecules are related by a pseudo twofold axis. Both molecules exhibit similar overall topography, rings A, B, C, and D adopting distorted sofa, chair, chair, and distorted envelope conformations, respectively.     

Recent progress in the use of ionic polymers as pseudostationary phases for EKC

This review concerns the introduction, characterization, and application of polymeric pseudostationary phases (PSPs) for EKC since 2004. Achiral and chiral polymers and separations are reviewed, as is the application of polymeric PSPs for the combination of EKC with mass spectrometric detection.     

The electronic states of but-2-yne studied by VUV absorption, near-threshold electron energy-loss spectroscopy and ab initio configuration interaction methods

The photoabsorption spectrum of but-2-yne in the range 5.5–11 eV (225–110 nm) has been recorded using a synchrotron radiation source. The spectrum is dominated by three d-type Rydberg series, converging to the first ionisation energy (IE) (π⁻¹, 9.562 eV). Origins of the π3d members are 7.841, 7.977 and 8.018 eV, respectively. Transitions of low intensity, arising from excitation of the π3s state (origin, 6.35 eV) and two π3p Rydberg states (7.38 and 7.51 eV, respectively) have also been identified in the spectrum. Near-threshold electron energy-loss spectra reveal valence excited triplet states at about 5.2 and 5.8 eV, respectively.Electronic excitation energies for valence and Rydberg-type states have been computed using ab initio multi-reference multi-root CI methods. These studies used a triple zeta + polarisation basis set, augmented by diffuse (Rydberg) orbitals, to generate the theoretical singlet and triplet energy manifolds. The correlation of theory and experiment shows the nature of the more intense Rydberg state types, and identification of the main valence and Rydberg bands. Calculated energies for Rydberg states are close to those expected, and there is generally a good correlation between the theoretical and experimental envelopes. It was possible to generate singlet Rydberg states which relate to the 5-lowest IEs of but-2-yne; furthermore, the separation of these sequences shows that the IE order (under D_3h symmetry) is: , also supported by direct calculation of the IEs by CI.The lowest valence singlet states are ππ^*, optically forbidden, and calculated to lie near 7.3 and 7.6 eV. The states which contribute strongly to the observed spectrum are πσ^* near 7.9 eV having excitation, followed by several ππ^* and πσ^* states between 10.0 and 10.5 eV; an ¹E′ antisymmetric combination(2e′2e″ − 2e′2e″) is by far the strongest in intensity. A further group of symmetry-allowed valence states are calculated to lie near 12.3 and 12.9 eV. The two lowest triplet states, both of E′ symmetry (ππ^*), have vertical excitation energies of 5.7 and 6.2 eV, but are strongly bent with a trans-CCCC unit (C_S and C_2h). The theoretical work confirms that, on intensity grounds, valence excited states do not contribute significantly to the spectrum. CI calculations of the ionic states give the ionisation energy sequence (D_3h): . Adiabatic structures for the first cation, two triplets, and a singlet (C_2h) were obtained; these show shortening of C–C, and lengthening of CC, in a trans-CCCC, as is found with ethyne.     

Transient spectral theory, stable and unstable cones and Gershgorin?s theorem for finite-time differential equations

Dynamical behaviour on a compact (finite-time) interval is called monotone-hyperbolic or M-hyperbolic if there exists an invariant splitting consisting of solutions with monotonically decreasing and increasing norms, respectively. This finite-time hyperbolicity notion depends on the norm. For arbitrary norms we prove a spectral theorem based on M-hyperbolicity and extend Gershgorin?s circle theorem to this type of finite-time spectrum. Similarly to stable and unstable manifolds, we characterize M-hyperbolicity by means of existence of stable and unstable cones. These cones can be explicitly computed for D-hyperbolic systems with norms induced by symmetric positive definite matrices and also for row diagonally dominant systems with the sup-norm, thus providing sufficient and computable conditions for M-hyperbolicity.     

An incommensurate thiourea inclusion compound

X-Ray diffraction studies reveal that the tunnel inclusion compound formed between 1-tert-butyl-4-iodobenzene and thiourea has an incommensurate relationship between the periodicities of the host and guest substructures along the tunnel axis, representing the first reported case of an incommensurate thiourea inclusion compound.     

A New Synthesis of Aromatic and Heteroaromatic Nitrogen Mustards Via 3-Pyrrolines

Reaction of aromatic and heteroaromatic halides with 3-pyrroline gives adducts which can be converted in a three-step process to nitrogen mustards.