X-Ray Structure Analysis of 15-Apoviolaxanth-15-al

The X-ray structure of 15-apoviolaxanth-15-al ( = (1′S,2′R,4′S,2E,4E,6E,8E)-9-(1′,2′-epoxy-4′-hydroxy-2′,6′,6′-trimethylcyclohexyl)-3,7-dimethylnona-2,4,6,8-tetraenal) is reported. The four symmetry-independent molecules in the asymmetric unit are linked into X-shaped spirals by intermolecular H-bonds. Additional H-bonds interconnect the spirals, forming wave-like chains. The geometry of the polyene side chain possesses the same in-plane bending observed for related retinal and carotenoid compounds. The polyene side chain deviates from planarity by twists of up to 10° about each bond; some of the largest twists are about C?C bonds. The epoxycyclohexane ring possesses a distorted ‘C(3)-sofa’ conformation. The torsion angles about the bond connecting the polyene chain to the cyclohexane ring are compared with equivalent torsion angles in molecules containing epoxide rings substituted with a π-system in order to examine possible interactions between the epoxide group and the π-system, either through pseudoconjugation, or through an interaction of the nonbonding orbitals of the epoxy O-atom with the π-orbitals of the polyene chain. The latter is considered to be more likely.     

The Crystal Structure of the Pentaphenylethane/Acetone Solvate by X-Ray Analysis

The crystal structure of the acetone solvate of pentaphenylethane (C₃₂H₂₆ · 1/2 C₃H₆O; monoclinic, a = 8.625, b = 16.587, c = 16.961 Å, β = 95.75°, space group P2₁/c, Z = 4) has been determined by X-ray analysis. The structure was solved by direct methods and refined to a final R of 0.056. The central ethane bond has a length of 1.612 (3) Å. The cavity enclosing the solvent retains the inversion centre in the crystal: as a consequence, a two-fold disordered orientation was observed for the acetone molecule. The rotational orientation of the methyl groups was found to be staggered with respect to the C, O-bond.     

X-Ray Structure of t-Butyldiazopyruvate and Its Theoretical Analysis Through a Variety of Computational Methods

The structure of the t-butyldiazopyruvate (1), an intermediate in the synthesis of DPTA-like ligands (DTPA = diethylenetriaminepentaacetic acid), has been determined by X-ray analysis. The molecule, which lies in a crystallographic mirror plane, is characterised by a cis arrangement of the two carbonylic oxygen atoms. Molecular mechanics and quantum mechanical molecular orbital calculations, at EHMO and ab initio levels, were performed in order to investigate the conformational properties of the isolated molecule. The packing effect has been examined by means of the program PROMET (5) by calculating the packing energies for a number of possible crystal structures. It is found that the energetic differences calculated for the various effects are small and comparable. Thus, the cis conformation found in the experimental structure is not in deep contrast with the theoretical calculations for the free molecule which favor the trans conformer. An energy barrier is detected by all of the computational methods when two CO functional groups lie in orthogonal planes. Importantly, a search in the Cambridge Structural Database indicates that all of the torsional conformations are possible in the 0–180° range. The complexity of the contrasting energetic factors is presented in some detail.     

Structure of a Tricyclic Photoproduct C15H24O3 by X-Ray Analysis

The crystal structure of the photoproduct 1 (C₁₅H₂₄O₃; monoclinic, a = 7.682, b = 14.448, c = 12.925 Å, β = 108.4°; space group P2₁/c, Z = 4) has been determined by X-ray analysis. The structure was solved by direct methods and the positions of all hydrogen atoms were obtained from a difference synthesis. The final R factor is 0.049. The polycyclic skeleton of 1 consists of a trans-decalone ring system axially fused to an oxolane ring in a conformation intermediate between the envelope and twist form. Strong intramolecular non-bonded interactions are observed among the substituent atoms.     

The X-Ray Structure Of 3,4,5,7-Tetra-O-Acetyl 2,6-Anhydro-D-Glycero-D-Talo-Heptonamide

Abstract

The title compound (C₁₅H₂₁NO₁₀)' M_r=375.34, crystallized in the orthorhombic space group P2₁2₁,2₁ with a=8.989(1), b=9.350(2), c=22.839(2)Å, V=1919.4(7)ų, Z=4 and Dc=1.299 Mgm^?3. The structure was solved by direct methods and refined to an R-index of 0.043. The compound is in the α-D-configuration and displays the ⁵C₂ conformation. The carbamoyl group is axially oriented and the remaining substituants are 3a, 4e, 5e and 6e. The absence of the anomeric effect in this C-glycoside results in equal and normal endocyclic C-O bond distances (1.425(3)Å). The carbamoyl nitrogen is involved in a bifurcated hydrogen bond, intramolecularly with the pyranosyl ring oxygen atom 0-6, and intermolecularly with the carbonyl oxygen atom 0-9.     

X-Ray Structure of a Heterochiral, Sulfoximine-Stabilized Dilithiomethane Derivative

A distorted Li(6)O octahedron in the center and four geminal dilithiated sulfoximine units characterize a tetrameric aggregate of the chiral sulfoximine-stabilized dilithiomethane derivative 3, a previously unknown reaction intermediate in asymmetric dianion chemistry. A comparison with the crystal structure of the monolithiated parent 2, formed by the treatment of 1 with nBuLi, allows a rationalization of the second lithiation.     

The Conformation of Sterically Congested Seven-Membered Rings Containing Tetracoordinate Germanium(IV): A First X-Ray Crystallographic Structure Determination

The X-ray crystallographic analysis of 6,6-dimethyl-2,4,8,10-tetra-tert-octyl-dibenzo[d,f][1,3,2]dioxagermepin, 1 is reported. In the solid-state conformation of 1, the dihedral angle about the C─C sp²-sp ² σ bond connecting the two aryl rings is 50.1°. The observed C₂ symmetry in the solid-state conformation of 1 is consistent with the previously suggested solution conformation.