Chair Conformation (chair + conformation)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Crystal structure of a polar nematogen 4-(trans- 4-undecylcyclohexyl) isothiocyanatobenzene

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2007
S. Biswas
Abstract Crystal and molecular structures of a nematogenic compound 4-(trans- 4-undecylcyclohexyl) isothiocyanatobenzene (11CHBT) have been determined by direct methods using single crystal X-ray diffraction data. The compound (C24H37N1S1) crystallizes in the monoclinic system with the space group P21/c and Z = 4. The unit cell parameters are a = 5.5539(11) Å, b = 8.1341(10) Å, c = 51.494(5) Å, and (= 91.127(14)0. The structure was refined to Rw = 0.051. The molecule is found to be slightly bow-shaped though the alkyl chain is in all- trans conformation. The phenyl ring and the alkyl chain are planar and the cyclohexyl group is in chair conformation. The isothiocyanato groups are almost linear. Parallel imbricated mode of packing of the molecules is found in the crystalline state which is precursor to the nematic phase structure. There are many van der Waals' interactions particularly in the isothiocyanato benzene part of the molecule. Of the various associated pairs of molecules the one having anti-parallel configuration with overlaps in the isothiocyanato phenyl group probably exists in both the crystalline and the nematic phases. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Structure and conformation of a nickel complex: {2-Hydroxo-3-piperidine-1-yl-methyl-N,N,(bis-5-bromobenzylpropylenediimine)nickel(II)perchlorate}

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2004
S. M. Malathy Sony
Abstract The title compound, a nickel complex [C23H26N3O2Br2Ni.(ClO4)] (CCDC 199520) crystallizes in triclinic space group P with the cell parameters a = 10.2560(4), b = 10.8231(4), c = 12.0888(5)Å, , = 99.404(1), , = 99.780(1), , = 92.252(1)° and V = 1301.49(9)Å3. The structure was solved by Patterson method and refined by full-matrix least-squares procedures to a final R = 0.0497 using 6287 observed reflections. In the complex, the piperidine ring takes chair conformation and the geometry around the Ni ion is slightly distorted square planar. The dihedral angle between the planes [N-Ni-N and O-Ni-O] is 9.4(1)°. The chelate ring containing both the nitrogen atoms adopts twisted boat conformation. The molecules in the crystal are stabilized by N-H,O and C-H,O types of hydrogen bonds in addition to a C-H,, interaction. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Thermal Behavior of Tetrahydropyran-Intercalated VOPO4: Structural and Dynamics Study

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2007
Klára Melánová
Abstract The thermal behavior of tetrahydropyran-(THP-)intercalated VOPO4 was probed by an extensive combination of experimental methods (XRD, DSC, FTIR, solid-state NMR) and quantum chemical calculations. Two temperature-induced transitions were detected and all polymorphs exhibit a high degree of molecular order and tight packing of THP in VOPO4. The first reversible thermal transition at around 100 °C was attributed to boat/chair conformation changes of the THP molecules. Most probably, a low-temperature boat conformation of the guest molecules present in the interlayer space of VOPO4 changes to a high-temperature chair conformation. This rearrangement of the THP molecules was confirmed by variable-temperature 13C CP/MAS NMR spectroscopy. Quantum chemical calculations using a B3LYP functional and 6-31G(d) basis set also support this idea. The second change at around 140 °C is probably caused by a weakening of the donor,acceptor bond between the oxygen molecule of THP and the vanadium atom of the host and the formation of a disorder in packing of the THP molecules. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


Screening the Structural Space of Bicyclo-DNA: Synthesis and Thermal Melting Properties of bc4,3 -DNA

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2009
Andrea Stauffiger
Abstract In attempts to screen the structural and functional properties of bicyclo-DNA, in which the ribose C(3,) and C(5,) centers are integrated into an additional five-membered carbocyclic ring ([3.3.0]-series) we have now synthesized and investigated a ring enlarged analogue in which C(5,) and C(3,) are spanned by a six-membered carbocyclic ring ([4.3.0]-series). The synthesis of the corresponding bc4,3 -T nucleoside 13 was performed in 12 steps by starting from known allyl furanose 1. X-ray analysis of its benzyl protected precursor 12 showed the cyclohexane ring to adopt a chair conformation with the O(5,) substituent in an axial position. The furanose part shows clearly S-type sugar pucker. This nucleoside was converted into the corresponding phosphoramidite building block 15 and incorporated into oligodeoxynucleotides by standard phosphoramidite chemistry. The thermal stabilities of oligonucleotides with single or double incorporations of bc4,3 -T residues, paired to complementary DNA or RNA, were found to be similar to those of unmodified oligonucleotides (,2.3 to +0.7 °C per modification) and to those with the known bc-T modifications. We also found that mismatch discrimination in the bc4,3 -T series was similar to that of the natural series but less discriminative in comparison to the known bc-T series.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


Formation of the B Ring in Steroids and Hopanoids from Squalene

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2004
B. Andes Hess Jr.
Abstract A theoretical conformational study based on density functional calculations provides evidence that the sterol and nonsterol cyclizations of squalene to triterpenes are controlled by conformational effects as has been previously suggested. It was found that different conformers of a model system of squalene give rise to the chair,boat conformation found in the steroids and the chair,chair conformation of the pentacyclic 3-deoxytriterpenes for their A and B rings. It is suggested that the enzymes play a key role in holding the substrate in the proper orientation for these cyclizations to occur. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]


Effect of Through-Bond Interaction on Conformation and Structure in Rod-Shaped Donor,Acceptor Systems.

HELVETICA CHIMICA ACTA, Issue 3 2003
Part
The crystal structures of five N -arylpiperidin-4-one derivatives 2P2, 3P2, 5P2, 1P3, and 2P3 are presented (Fig.,2 and Tables,1,5) and discussed together with the derivatives 1P2 and 4P2 published previously. In all but one structure, 1P2, the aryl group is in an equatorial position. The piperidine ring adopts a normal chair conformation. In 1P2, the piperidine ring central CC bonds are significantly elongated, which is consistent with the idea that through-bond interaction is more pronounced in the axial conformation. Through-bond interaction also influences the pyramidalization at the piperidine C(4)-atom in such a way that a strong interaction is directing the ethylene C-atom C(9) into the axial direction. [source]


Synthesis and conformational study of P -heterocyclic androst-5-ene derivatives

HETEROATOM CHEMISTRY, Issue 1 2008
Éva Frank
The reactions of (20R)-3,-acetoxy-21-hydroxymethylpregn-5-en-20-ol (2) and (20R)-3,-acetoxypregn-5-ene-20,21-diol (11) with phenylphosphonic dichloride 3 and aryl dichlorophosphates 4,6 afforded novel types of P -heterocyclic androst-5-ene derivatives 7,10 and 12 as epimeric pairs. The diastereomers were separated by column chromatography and were characterized by NMR spectroscopy. Estimation of the stereostructures of the corresponding epimers by B3LYP/631G(d) DFT ab initio calculations suggested that the six-membered hetero ring in compounds 7b and 8a,10a adopts predominantly a chair conformation, with the P -substituents in their preferred orientation. The cyclic phosphonate moiety in 7a or 8b,10b, however, seems to exist as an equilibrium mixture of chair,distorted- boat or chair,chair forms. The theoretical calculations indicate that the conformational equilibrium is shifted toward the distorted- boat conformer for 7a, with a pseudoequatorial P -phenyl substituent, whereas for 8b,10b the chair conformer with an equatorial P -phenoxy group predominates. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:7,14, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20372 [source]


DFT conformational studies of ,-maltotriose,

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2008
Udo Schnupf
Abstract Recent DFT optimization studies on ,-maltose improved our understanding of the preferred conformations of ,-maltose. The present study extends these studies to ,-maltotriose with three ,- D -glucopyranose residues linked by two ,-[1,4] bridges, denoted herein as DP-3's. Combinations of gg, gt, and tg hydroxymethyl groups are included for both "c" and "r" hydroxyl rotamers. When the hydroxymethyl groups are for example, gg-gg-gg, and the hydroxyl groups are rotated from all clockwise, "c", to all counterclockwise, "r", the minimum energy positions of the bridging dihedral angles (,H and ,H) move from the region of conformational space of (,, ,), relative to (0°, 0°), to a new position defined by (+, +). Further, it was found previously that the relative energies of ,-maltose gg-gg-c and "r" conformations were very close to one another; however, the DP-3's relative energies between hydroxyl "c" or "r" rotamers differ by more than one kcal/mol, in favor of the "c" form, even though the lowest energy DP-3 conformations have glycosidic dihedral angles similar to those found in the ,-maltose study. Preliminary solvation studies using COSMO, a dielectric solvation method, point to important solvent contributions that reverse the energy profiles, showing an energy preference for the "r" forms. Only structures in which the rings are in the chair conformation are presented here. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source]


A new GROMOS force field for hexopyranose-based carbohydrates

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2005
Roberto D. Lins
Abstract A new parameter set (referred to as 45A4) is developed for the explicit-solvent simulation of hexopyranose-based carbohydrates. This set is compatible with the most recent version of the GROMOS force field for proteins, nucleic acids, and lipids, and the SPC water model. The parametrization procedure relies on: (1) reassigning the atomic partial charges based on a fit to the quantum-mechanical electrostatic potential around a trisaccharide; (2) refining the torsional potential parameters associated with the rotations of the hydroxymethyl, hydroxyl, and anomeric alkoxy groups by fitting to corresponding quantum-mechanical profiles for hexopyranosides; (3) adapting the torsional potential parameters determining the ring conformation so as to stabilize the (experimentally predominant) 4C1 chair conformation. The other (van der Waals and nontorsional covalent) parameters and the rules for third and excluded neighbors are taken directly from the most recent version of the GROMOS force field (except for one additional exclusion). The new set is general enough to define parameters for any (unbranched) hexopyranose-based mono-, di-, oligo- or polysaccharide. In the present article, this force field is validated for a limited set of monosaccharides (,- and ,-D-glucose, ,- and ,-D-galactose) and disaccharides (trehalose, maltose, and cellobiose) in solution, by comparing the results of simulations to available experimental data. More extensive validation will be the scope of a forthcoming article. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1400,1412, 2005 [source]


First-principle studies of intermolecular and intramolecular catalysis of protonated cocaine

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2005
Chang-Guo Zhan
Abstract We have performed a series of first-principles electronic structure calculations to examine the reaction pathways and the corresponding free energy barriers for the ester hydrolysis of protonated cocaine in its chair and boat conformations. The calculated free energy barriers for the benzoyl ester hydrolysis of protonated chair cocaine are close to the corresponding barriers calculated for the benzoyl ester hydrolysis of neutral cocaine. However, the free energy barrier calculated for the methyl ester hydrolysis of protonated cocaine in its chair conformation is significantly lower than for the methyl ester hydrolysis of neutral cocaine and for the dominant pathway of the benzoyl ester hydrolysis of protonated cocaine. The significant decrease of the free energy barrier, ,4 kcal/mol, is attributed to the intramolecular acid catalysis of the methyl ester hydrolysis of protonated cocaine, because the transition state structure is stabilized by the strong hydrogen bond between the carbonyl oxygen of the methyl ester moiety and the protonated tropane N. The relative magnitudes of the free energy barriers calculated for different pathways of the ester hydrolysis of protonated chair cocaine are consistent with the experimental kinetic data for cocaine hydrolysis under physiologic conditions. Similar intramolecular acid catalysis also occurs for the benzoyl ester hydrolysis of (protonated) boat cocaine in the physiologic condition, although the contribution of the intramolecular hydrogen bonding to transition state stabilization is negligible. Nonetheless, the predictability of the intramolecular hydrogen bonding could be useful in generating antibody-based catalysts that recruit cocaine to the boat conformation and an analog that elicited antibodies to approximate the protonated tropane N and the benzoyl O more closely than the natural boat conformer might increase the contribution from hydrogen bonding. Such a stable analog of the transition state for intramolecular catalysis of cocaine benzoyl-ester hydrolysis was synthesized and used to successfully elicit a number of anticocaine catalytic antibodies. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 980,986, 2005 [source]


Structural, spectroscopic, and theoretical studies of a very short OHO hydrogen bond in bis(4-(N -methylpiperidinium)-butyrate) hydrobromide

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2009
bieta Bartoszak-Adamska
Abstract The molecular structure of bis(4-(N -methylpiperidinium)-butyrate) hydrobromide, (MPBu)2HBr, has been characterized by single crystal X-ray diffraction, infrared and NMR spectroscopies, and by DFT calculations. The crystals of the title compound at 140,K are monoclinic, space group C2/c, with a,=,11.7118(4), b,=,7.8737(2), c,=,23.9240(8),Å3,, ,,=,90.431(3)°, V,=,2206.1(1),Å3, and Z,=,4. Two 4-(N -methylpiperidinium)-butyrate moieties are joined by a very short and centrosymmetric O.H.O hydrogen bond of 2.436(2),Å3,. The piperidine ring adopts a chair conformation with the methyl group in the equatorial and the bulky (CH2)3COO substituent in the axial position. The broad absorption band below 1500,cm,1 in the FTIR spectrum confirms the existence of a very short O,H,O hydrogen bond. The 1H and 13C NMR spectra are interpreted on the basis of 2D experiments and the calculated GIAO/B3LYP/6-31G(d,p) magnetic isotropic shielding tensors. In the optimized structure of the complex, a 4-(N -methylpiperidinium)-butyrate zwitterion interacts with a 4-(N -methylpiperidinium)-butyric acid cation forming an O,. HO hydrogen bond of 2.580,Å3,. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Comparison of 17,-estradiol structures from x-ray diffraction and solution NMR

MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2005
Fernando Commodari
Abstract The NMR-derived structure of estrogen (17,-estradiol, E2), the drug of choice for postmenopausal women, was compared with a recent literature crystal x-ray structure of Fab-bound E2. 1H and 13C NMR spectra of E2 were acquired in DMSO- d6. Assignments were obtained from an analysis of DQF-COSY, TOCSY, HETCOR, HMQC and HMBC 2D NMR spectra. The 1H and 13C NMR assignments are the first reported for E2 in DMSO- d6. Two solution structures, S1 and S2, were obtained with molecular modeling using NOE constraints. S1 overlaps with the crystal structure for all rings. S2 shows prominent differences in the C-ring (C9C11C12C13) segment, which deviates from a chair conformation, and excellent overlap in the A-, B- and D-rings of E2. The C-ring in S2 adopts a boat conformation as opposed to a chair conformation in the x-ray and S1 structures. The S2 structure is about 6° more twisted than the bound x-ray and S1 models. The S1, S2 and x-ray structures had ring bowing values of 10.1 ± 0.3, 11 ± 1 and 10.37°, respectively. Of the 100 solution conformers generated, 83 had S1 conformation and 17 had S2 conformation, with average internal energies of 112 ± 2 and 141 ± 2 kcal mol,1, respectively. The 100 S1 - and S2 - derived conformers showed a r.m.s.d. of 0.72 Å for all atoms. The x-ray, S1 and S2 C18O17 distances were 2.93, 2.92 ± 0.01 and 2.93 ± 0.01 Å, respectively, and the O3O17 distances were 11.06, 11.18 ± 0.12, and 10.89 ± 0.05 Å, respectively. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Polymorphism in the nitrate salt of the [Mn(acetylacetonate)2(H2O)2]+ ion

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010
A. R. Biju
The crystallization of [Mn(acac)2(H2O)2]+ from solutions containing excess nitrate leads to the formation of four polymorphs. All polymorphs contain two different types of complex ions, one containing essentially coplanar acac ligands and the other in which the two acac ligands together assume a chair conformation. Molecular modelling using DFT (density-functional theory) calculations shows that the coplanar conformation is the electronically stable one. The hydrogen bonding between the trans -water molecules and the nitrate ion produces a one-dimensional chain of 12-membered rings, which are further organized into a two-dimensional network via a lattice water molecule. Lattice-energy calculations have been carried out to compare the stabilities of the four polymorphs. [source]


Structure and conformational analysis of a bidentate pro-ligand, C21H34N2S2, from powder synchrotron diffraction data and solid-state DFTB calculations

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2009
Edward E. Ávila
The molecular and crystalline structure of ethyl 1,,2,,3,,4,,4a,,5,,6,,7,-octahydrodispiro[cyclohexane-1,2,-quinazoline-4,,1,,-cyclohexane]-8,-carbodithioate (I) was solved and refined from powder synchrotron X-ray diffraction data. The initial model for the structural solution in direct space using the simulated annealing algorithm implemented in DASH [David et al. (2006). J. Appl. Cryst.39, 910,915] was obtained performing a conformational study on the fused six-membered rings of the octahydroquinazoline system and the two spiran cyclohexane rings of (I). The best model was chosen using experimental evidence from 1H and 13C NMR [Contreras et al. (2001). J. Heterocycl. Chem.38, 1223,1225] in combination with semi-empirical AM1 calculations. In the refined structure the two spiran rings have the chair conformation, while both of the fused rings in the octahydroquinazoline system have half-chair conformations compared with in-vacuum density-functional theory (DFT) B3LYP/6-311G*, DFTB (density-functional tight-binding) theoretical calculations in the solid state and other related structures from X-ray diffraction data. Compound (I) presents weak intramolecular hydrogen bonds of the type N,H...S and C,H...S, which produce delocalization of the electron density in the generated rings described by graph symbols S(6) and S(5). Packing of the molecules is dominated by van der Waals interactions. [source]


Structures of furanosides: geometrical analysis of low-temperature X-ray and neutron crystal ­structures of five crystalline methyl ­pentofuranosides

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2001
Artem Evdokimov
Crystal structures of all five crystalline methyl d -pentofuranosides, methyl ,- d -arabinofuranoside (1), methyl ,- d -arabinofuranoside (2), methyl ,- d -lyxofuranoside (3), methyl ,- d -ribofuranoside (4) and methyl ,- d -xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate, unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C1 chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations. [source]


Poly[(,6 - rac - cis -cyclohexane-1,2-dicarboxylato)strontium]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010
Karen A. Robertson
In the title layered coordination polymer, [Sr(C8H10O4)]n, the strontium ion adopts a distorted square-antiprismatic SrO8 geometry, arising from its coordination by six different cis -cyclohexane-1,2-dicarboxylate dianions (two bidentate and four monodentate). Within the dianion, the cyclohexane ring adopts a chair conformation and the dihedral angle between the planes of the ,CO2, groups is 80.4,(6)°. The polyhedral linkage pattern leads to (100) sheets in the crystal in which the SrO8 groups share triangular faces and edges in which the Sr...Sr topological connectivity is a 63 net. The crystal studied was a nonmerohedral twin, with the components related by a 180° rotation about [100]. [source]


Peracetylated ,- d -glucopyranosyl fluoride and peracetylated ,-maltosyl fluoride

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010
Simone Dedola
The X-ray analyses of 2,3,4,6-tetra- O -acetyl-,- d -glucopyranosyl fluoride, C14H19FO9, (I), and the corresponding maltose derivative 2,3,4,6-tetra- O -acetyl-,- d -glucopyranosyl-(1,4)-2,3,6-tri- O -acetyl-,- d -glucopyranosyl fluoride, C26H35FO17, (II), are reported. These add to the series of published ,-glycosyl halide structures; those of the peracetylated ,-glucosyl chloride [James & Hall (1969). Acta Cryst. A25, S196] and bromide [Takai, Watanabe, Hayashi & Watanabe (1976). Bull. Fac. Eng. Hokkaido Univ.79, 101,109] have been reported already. In our structures, which have been determined at 140,K, the glycopyranosyl ring appears in a regular 4C1 chair conformation with all the substituents, except for the anomeric fluoride (which adopts an axial orientation), in equatorial positions. The observed bond lengths are consistent with a strong anomeric effect, viz. the C1,O5 (carbohydrate numbering) bond lengths are 1.381,(2) and 1.381,(3),Å in (I) and (II), respectively, both significantly shorter than the C5,O5 bond lengths, viz. 1.448,(2),Å in (I) and 1.444,(3),Å in (II). [source]


3,3,6,6,9,9-Hexaethyl-1,2,4,5,7,8-hexaoxacyclononane at 296 K

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009
Jorge Cerna
The title molecule (diethyl ketone triperoxide, DEKTP), C15H30O6, is a cyclic triperoxide closely related to triacetone triperoxide (TATP), one of the most unstable explosives known. However, the stability of DEKTP is ca 20,50 times greater than that of TATP. DEKTP crystallizes with two molecules in the asymmetric unit, with virtually identical geometry. The cyclononane core is stabilized in a twisted boat,chair conformation (approximate D3 symmetry), very close to that previously described for TATP. The explanation for the safe thermal behaviour of DEKTP compared with TATP should thus not be sought in the molecular dimensions, but rather in the thermal decomposition kinetics. [source]


rac -5-Diphenylacetyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine and rac -5-formyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009
Thanikasalam Kanagasabapathy
rac -5-Diphenylacetyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine, C26H27NOS, (I), and rac -5-formyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine, C13H17NOS, (II), are both characterized by a planar configuration around the heterocyclic N atom. In contrast with the chair conformation of the parent benzothiazepine, which has no substituents at the heterocyclic N atom, the seven-membered ring adopts a boat conformation in (I) and a conformation intermediate between boat and twist-boat in (II). The molecules lack a symmetry plane, indicating distortions from the perfect boat or twist-boat conformations. The supramolecular architectures are significantly different, depending in (I) on C,H...O interactions and intermolecular S...S contacts, and in (II) on a single aromatic ,,, stacking interaction. [source]


trans -Decahydronaphthalene (decalin) from powder diffraction data

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2009
Stefan Eibl
The title compound, C10H18, a decalin stereoisomer, crystallizes with Z, = 0.5 in the space group P21/n. The trans -decalin molecule is located on an inversion centre with both rings in a chair conformation, making for a quasi-flat overall shape. Despite the absence of hydrogen bonds, it crystallizes easily. In this work the unknown crystal structure of trans -decalin has been solved and refined using X-ray powder diffraction data. [source]


Absolute structures and conformations of the spongian diterpenes spongia-13(16),14-dien-3-one, epispongiadiol and spongiadiol

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009
Ken W. L. Yong
The absolute configurations of spongia-13(16),14-dien-3-one [systematic name: (3bR,5aR,9aR,9bR)-3b,6,6,9a-tetramethyl-4,5,5a,6,8,9,9a,9b,10,11-decahydrophenanthro[1,2- c]furan-7(3bH)-one], C20H28O2, (I), epispongiadiol [systematic name: (3bR,5aR,6S,7R,9aR,9bR)-7-hydroxy-6-hydroxymethyl-3b,6,9a-trimethyl-3b,5,5a,6,7,9,9a,9b,10,11-decahydrophenanthro[1,2- c]furan-8(4H)-one], C20H28O4, (II), and spongiadiol [systematic name: (3bR,5aR,6S,7S,9aR,9bR)-7-hydroxy-6-hydroxymethyl-3b,6,9a-trimethyl-3b,5,5a,6,7,9,9a,9b,10,11-decahydrophenanthro[1,2- c]furan-8(4H)-one], C20H28O4, (III), were assigned by analysis of anomalous dispersion data collected at 130,K with Cu K, radiation. Compounds (II) and (III) are epimers. The equatorial 3-hydroxyl group on the cyclohexanone ring (A) of (II) is syn with respect to the 4-hydroxymethyl group, leading to a chair conformation. In contrast, isomer (III), where the 3-hydroxyl group is anti to the 4-hydroxymethyl group, is conformationally disordered between a major chair conformer where the OH group is axial and a minor boat conformer where it is equatorial. In compound (I), a carbonyl group is present at position 3 and ring A adopts a distorted-boat conformation. [source]


2,3,4,6-Tetra- O -acetyl-,- d -glucopyranosyl azide

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2008
Simone Dedola
The CuI -catalysed 1,3-dipolar cycloaddition of an azide and a terminal alkyne is becoming an increasingly popular tool for synthetic chemists. This is the most representative of the so-called `click reactions' and it is used to generate 1,4-disubstituted triazoles in high yield. During studies on such cycloaddition reactions, a reduced reactivity of an ,-glucosyl azide with respect to the corresponding ,-anomer was observed. With the aim of understanding this phenomenon, the structure of the title compound, C14H19N3O9, has been determined at 140,K. The glucopyranosyl ring appears in a regular 4C1 chair conformation with all the substituents in equatorial positions, except for the anomeric azide group, which adopts an axial orientation. The observed bond lengths are consistent with a strong anomeric effect, which is reflected in a change in dipolar character and hence reduced reactivity of the ,-glucosyl azide. [source]


18-De­oxy-13,,14-dihydrolycoctam: the lycoctamone rearrangement confirmed

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2006
Michael Benn
The structure of the title compound, C23H35NO4, contains a unique penta­cyclic ring system wherein one cyclo­hexyl ring adopts a chair conformation, two cyclo­hexyl rings are in boat conformations, and a six-membered heterocyclic ring and a cyclo­pentyl ring are in envelope conformations. The structures of the lycoctamones, ,,,-unsaturated aldehydes produced by acid-catalyzed degradation of lactams of lycoctonine-type alkaloids, previously deduced from the results of extensive chemical investigations have been proven to be correct by the determination of the crystal structure of this compound. [source]


Unprecedented self-assembled cyclic hexamer of ferrocenyldimethylsilanol, [FcSiMe2OH]6 (Fc = (,5 -C5H5)Fe(,5 -C5H4)),,

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 4 2005
Hemant K. Sharma
Abstract Ferrocenyldimethylsilanol, FcSiMe2OH, Fc = (,5 -C5H5)Fe(,5 -C5H4), features a self-assembled (through intermolecular hydrogen bonding) cyclohexameric supermolecule with a chair conformation. Copyright © 2005 John Wiley & Sons, Ltd. [source]


1-Phenyl-5-(piperidino­methyl)-1H -tetrazole

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2004
Alexander S. Lyakhov
In the mol­ecule of the title 1,5-disubstituted tetrazole, C13H17N5, the tetrazole and benzene rings are not coplanar, having a dihedral angle of 42.96,(5)° between them. The piperidine fragment adopts a chair conformation, and there is a non-classical intramolecular contact between the benzene H atom and the piperidine N atom. Intermolecular C,H,, interactions involving the piperidine C,H groups and the benzene rings are responsible for the formation of two-dimensional networks, extending parallel to the ab plane. These networks are linked together into a three-dimensional polymeric structure via,,, stacking interactions between the tetrazole rings of two adjacent mol­ecules. [source]


3,3,6,6-Tetra­methyl-1,2,4,5-tetroxane: a twinned crystal structure

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2004
Feyissa Gadissa Gelalcha
The title compound, C6H12O4, also known as dimeric acetone peroxide, Me2(C2O4)Me2, has crystallographically imposed inversion symmetry and adopts a chair conformation in the solid state. This structure contrasts with that of the sulfur homologue Me2(C2S4)Me2, which has crystallographically imposed symmetry and crystallizes in a twist-boat conformation. Crystals of the title compound are twinned along the reciprocal c* axis. [source]


(S)- trans -Cyclohexane-1,2-dicarboximide

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2002
Maria Gdaniec
The molecule of the title compound, C8H11NO2, contains a strained bicyclic system with a significantly twisted imide chromophore. The five-membered ring fragment containing the imide function is strongly puckered and adopts a half-chair conformation. The six-membered ring has a slightly distorted chair conformation. The mol­ecules are joined by strong N,H,O and weak C,H,O hydrogen bonds into infinite chains. [source]


N1,N1 -Diethyl- N2 -(2,3,4,6-tetra- O -acetyl-,- d -glucopyranosyl)acet­amidine

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2001
María Jesús Diánez
The solid-state conformation of the title compound, C20H32N2O9, has been determined at 150,K. The pyran­ose ring has a distorted chair conformation. Among the possible conformations of the C,N glycosidic bond, that of the E rotamer is observed and a short intramolecular Cmethyl,O contact may partly stabilize this conformation. Crystal cohesion is stabilized by an extensive network of weak C,H,O hydrogen bonds and close contacts. [source]


Di­spiro­[fluorene-9,5,-[1,2,3,4]­tetra­thia­ne-6,,9,,-fluorene]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2001
Anthony Linden
The tetra­thia­ne ring of the title compound, C26H16S4, has a chair conformation and the mol­ecule has approximate C2 symmetry. Each of the two fluorene ring systems is virtually planar, with the ring planes intersecting at an angle of 67.58,(5)°. This novel compound has been formed as a side product from the treatment of 9H -fluorene-9-thione with methyl N -[(benzyl­idene)­phenyl]­glycinate in the presence of LiBr and 1,6-di­aza­bi­cyclo­[5.4.0]­un­decane. [source]


(2R,3R,5R)-2-[(2R,3aS,6aR)-2,3,3a,4,5,6a-Hexa­hydro­furo­[2,3- b]­furan-2-yl]-5-isoprop­en­yl-2,3-di­methyl­cyclo­hexanone and (4aR,5S,7R)-5-isopropenyl-7,8,8-tri­methyl-2,3,4,4a,5,6,7,8-octa­hydro­naphthalene-4a-carbo­nitrile

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2000
Dianne D. Ellis
The molecular structures of two chiral cyclo­hexanones based on R -(,)-carvone, C17H26O3, (I), and C17H23NO, (II), are reported here. The six-membered ring in (I) is in a chair conformation with the two fused five-membered rings of the furo­furan­yl substituent in a cis configuration. Compound (II) contains a decalin group; one ring has the chair form whilst the other is in a half-boat conformation. Both products have been characterized spectroscopically, however, neither NMR nor IR results could prove the stereochemistry at each chiral centre unambiguously. The crystal analyses were used to ex­amine conformational properties of the compounds. [source]