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Half-chair Conformation (half-chair + conformation)

Distribution by Scientific Domains

Chemistry	92%

Selected Abstracts

Crystal structure of 4'-O-methylalpinumisoflavone at 90K

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006
R. Kingsford-Adaboh
Abstract 4,-O-Methylalpinumisoflavone crystals which hitherto had been difficult to crystallize for X-ray diffraction analyses have been obtained from a demethylated product of O, O-dimethylalpinumisoflavone. The structural and conformational features of the crystal measured at 90 K are reported and compared with previously reported work of O,O-dimethylalpinumisoflavone and 5-O-methyl-4,-O-(3-methyl-but-2-en-1-yl) alpinumisoflavone. Each of these compounds is characterized by a six membered ring that is further fused to a benzopyrone isoflavone moiety resulting in a tricyclic ring system. This six membered ring shows a half-chair conformation in all the molecules studied, with the ring in the title compound showing the least Cremer-Pople puckering amplitude Q and shorter inter and intramolecular contacts. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

New oxidized sterols from Aspergillus awamori and the endo -boat conformation adopted by the cyclohexene oxide system

MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2010
Hao Gao
Abstract Two new oxidized sterols 1 and 2 were obtained from the active fraction of a mangrove fungus Aspergillus awamori isolated from the soils around the mangrove plant Acrostichum speciosum. Their structures were elucidated using spectroscopic methods as 22E -7,-methoxy-5,,6,-epoxyergosta-8(14),22-dien-3,-ol (1) and 22E -3,-hydroxy-5,,6,,8,,14,-diepoxyergosta-22-en-7-one (2). The NMR data and complete assignments for both DMSO- d6 and CDCl3 were given. Their cytotoxic activity against A549 cell line was evaluated. Furthermore, the detailed conformation analysis for ring B (cyclohexene oxide system) of sterol 1 was given on the basis of NOEs. The endo -boat conformation was considered as the preferred conformation for ring B rather than half-chair conformation. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Eight 7-benzyl-3- tert -butyl-1-phenylpyrazolo[3,4- d]oxazines, encompassing structures containing no intermolecular hydrogen bonds, and hydrogen-bonded structures in one, two or three dimensions

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009
Juan C. Castillo
7-Benzyl-3- tert -butyl-1-phenyl-6,7-dihydro-1H,4H -pyrazolo[3,4- d][1,3]oxazine, C22H25N3O, (I), and 3- tert -butyl-7-(4-methylbenzyl)-1-phenyl-6,7-dihydro-1H,4H -pyrazolo[3,4- d][1,3]oxazine, C23H27N3O, (II), are isomorphous in the space group P21, and molecules are linked into chains by C,H...O hydrogen bonds. In each of 3- tert -butyl-7-(4-methoxybenzyl)-1-phenyl-6,7-dihydro-1H,4H -pyrazolo[3,4- d][1,3]oxazine, C23H27N3O2, (III), which has cell dimensions rather similar to those of (I) and (II), also in P21, and 3- tert -butyl-1-phenyl-7-[4-(trifluoromethyl)benzyl]-6,7-dihydro-1H,4H -pyrazolo[3,4- d][1,3]oxazine, C23H24F3N3O, (IV), there are no direction-specific interactions between the molecules. In 3- tert -butyl-7-(4-nitrobenzyl)-1-phenyl-6,7-dihydro-1H,4H -pyrazolo[3,4- d][1,3]oxazine, C22H24N4O3, (V), a combination of C,H...O and C,H...N hydrogen bonds links the molecules into complex sheets. There are no direction-specific interactions between the molecules of 3- tert -butyl-7-(2,3-dimethoxybenzyl)-1-phenyl-6,7-dihydro-1H,4H -pyrazolo[3,4- d][1,3]oxazine, C24H29N3O3, (VI), but a three-dimensional framework is formed in 3- tert -butyl-7-(3,4-methylenedioxybenzyl)-1-phenyl-6,7-dihydro-1H,4H -pyrazolo[3,4- d][1,3]oxazine, C23H25N3O3, (VII), by a combination of C,H...O, C,H...N and C,H...,(arene) hydrogen bonds, while a combination of C,H...O and C,H...,(arene) hydrogen bonds links the molecules of 3- tert -butyl-1-phenyl-7-(3,4,5-trimethoxybenzyl)-6,7-dihydro-1H,4H -pyrazolo[3,4- d][1,3]oxazine, C25H31N3O4, (VIII), into complex sheets. In each compound, the oxazine ring adopts a half-chair conformation, while the orientations of the pendent phenyl and tert -butyl substituents relative to the pyrazolo[3,4- d]oxazine unit are all very similar. [source]

4-Benzoyl-3,4-dihydro-2H -1,4-benzoxazine-2-carbonitrile: refinement using a multipolar atom model

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009
Krzysztof Ejsmont
The structural model for the title compound, C16H12N2O2, was refined using a multipolar atom model transferred from an experimental electron-density database. The refinement showed some improvements of crystallographic statistical indices when compared with a conventional spherical neutral-atom refinement. The title compound adopts a half-chair conformation. The amide N atom lies almost in the plane defined by the three neighbouring C atoms. In the crystal structure, molecules are linked by weak intermolecular C,H...O and C,H..., hydrogen bonds. [source]

The influence of sulfur substituents on the molecular geometry and packing of thio derivatives of N -methylphenobarbital

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009
Alicja Janik
The room-temperature crystal structures of four new thio derivatives of N -methylphenobarbital [systematic name: 5-ethyl-1-methyl-5-phenylpyrimidine-2,4,6(1H,3H,5H)-trione], C13H14N2O3, are compared with the structure of the parent compound. The sulfur substituents in N -methyl-2-thiophenobarbital [5-ethyl-1-methyl-5-phenyl-2-thioxo-1,2-dihydropyrimidine-4,6(3H,5H)-dione], C13H14N2O2S, N -methyl-4-thiophenobarbital [5-ethyl-1-methyl-5-phenyl-4-thioxo-3,4-dihydropyrimidine-2,6(1H,5H)-dione], C13H14N2O2S, and N -methyl-2,4,6-trithiophenobarbital [5-ethyl-1-methyl-5-phenylpyrimidine-2,4,6(1H,3H,5H)-trithione], C13H14N2S3, preserve the heterocyclic ring puckering observed for N -methylphenobarbital (a half-chair conformation), whereas in N -methyl-2,4-dithiophenobarbital [5-ethyl-1-methyl-5-phenyl-2,4-dithioxo-1,2,3,4-tetrahydropyrimidine-6(5H)-one], C13H14N2OS2, significant flattening of the ring was detected. The number and positions of the sulfur substituents influence the packing and hydrogen-bonding patterns of the derivatives. In the cases of the 2-thio, 4-thio and 2,4,6-trithio derivatives, there is a preference for the formation of a ring motif of the R22(8) type, which is also a characteristic of N -methylphenobarbital, whereas a C(6) chain forms in the 2,4-dithio derivative. The preferences for hydrogen-bond formation, which follow the sequence of acceptor position 4 > 2 > 6, confirm the differences in the nucleophilic properties of the C atoms of the heterocyclic ring and are consistent with the course of N -methylphenobarbital thionation reactions. [source]

Two polymorphs of 20-desmethyl-,-carotene

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2008
Madeleine Helliwell
Two polymorphs of 20-desmethyl-,-carotene (systematic name: 20-nor-,,,-carotene), C39H54, in monoclinic and triclinic space groups, were formed in the same vial by recrystallization from pyridine and water. Each polymorph crystallizes with the complete molecule as the asymmetric unit, and the two polymorphs show differing patterns of disorder. The , end rings of both polymorphs have the 6- s - cis conformation, and are twisted out of the plane of the polyene chain by angles of ,53.2,(8) and 47.3,(8)° for the monoclinic polymorph, and ,43.6,(3) and 56.1,(3)° for the triclinic polymorph. The cyclohexene end groups are in the half-chair conformation, but the triclinic polymorph shows disorder of one ring. Overlay of the molecules shows that they differ in the degree of nonplanarity of the polyene chains and the angles of twist of the end rings. The packing arrangements of the two polymorphs are quite different, with the monoclinic polymorph showing short intermolecular contacts of the disordered methyl groups with adjacent polyene chain atoms, and the triclinic polymorph showing ,,, stacking interactions of the almost parallel polyene chains. The determination of the crystal structures of the two title polymorphs of 20-desmethyl-,-carotene allows information to be gained regarding the structural effects on the polyene chain, as well as on the end groups, versus that of the parent compound ,-carotene. The absence of the methyl group is known to have an impact on various functions of the title compound. [source]

Four 2-aryl-8,8-dimethyl-6,7,8,9-tetrahydropyrazolo[2,3- a]quinazolin-6-ones: isolated molecules, hydrogen-bonded dimers, and ,-stacked chains of hydrogen-bonded dimers

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2006
Silvia Cruz
In each of the three compounds 2-(4-chlorophenyl)-5,8,8-trimethyl-6,7,8,9-tetrahydropyrazolo[2,3- a]quinazolin-6-one, C19H18ClN3O, (I), 2-(4-methoxyphenyl)-5,8,8-trimethyl-6,7,8,9-tetrahydropyrazolo[2,3- a]quinazolin-6-one, C20H21N3O2, (II), and 8,8-dimethyl-2-(4-methylphenyl)-6,7,8,9-tetrahydropyrazolo[2,3- a]quinazolin-6-one monohydrate, C19H19N3O·H2O, (IV), the non-aromatic carbocyclic ring adopts a half-chair conformation, while in 2-(4-chlorophenyl)-8,8-dimethyl-5-phenyl-6,7,8,9-tetrahydropyrazolo[2,3- a]quinazolin-6-one, C24H20ClN3O, (III), the corresponding ring adopts a conformation intermediate between the envelope and screw,boat forms. The structure of (I) consists of isolated molecules, while that of (II) contains dimers formed by C,H,O hydrogen bonds. In (III), dimers formed by C,H,O hydrogen bonds are linked into chains by means of an aromatic ,,, stacking interaction, while in the monohydrate, (IV), the heterocyclic molecules and the water molecules are linked by O,H,O and O,H,N hydrogen bonds to form centrosymmetric four-component aggregates. [source]

Conformations of three heterocyclic perhydropyrrolobenzofurans and polymeric assembly via co-operative intermolecular C,H,O hydrogen bonds

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2006
H. S. Yathirajan
In 1-cyclohexyl-6,6,8a-trimethyl-3a,6,7,8a-tetrahydro-1H -1-benzofuro[2,3- b]pyrrole-2,4(3H,5H)-dione, C19H27NO3, (I), and the isomorphous compounds 6,6,8a-trimethyl-1-phenyl-3a,6,7,8a-tetrahydro-1H -1-benzofuro[2,3- b]pyrrole-2,4(3H,5H)-dione, C19H21NO3, (II), and 6,6,8a-trimethyl-1-(3-pyridyl)-3a,6,7,8a-tetrahydro-1H -1-benzofuro[2,3- b]pyrrole-2,4(3H,5H)-dione, C18H20N2O3, (III), the tetrahydrobenzo,dihydrofuro,pyrrolidine ring systems are folded at the cis junction of the five-membered rings, giving rise to a non-planar shape of the tricyclic cores. The dihydrofuran and pyrrolidine rings in (I) are puckered and adopt an envelope conformation. The cyclohexene rings adopt a half-chair conformation in all the molecules, while the substituent N -cyclohexyl ring in (I) assumes a chair form. Short intramolecular C,H,O contacts form S(5) and S(6) motifs. The isomorphous compounds (II) and (III) are effectively isostructural, and aggregate into chains via intermolecular C,H,O hydrogen bonds. [source]

Dimethyl 3,4,5,5-tetraphenyl-1,3-thiazolidine-2,2-dicarboxylate and 3,3-dichloro-2,2,4,4,3,-pentamethyl- r -2,,t -4,-diphenylcyclobutane-1-spiro-5,-1,3-thiazolidine

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2004
gorzata Domaga
The first of the title compounds, C31H27NO4S, (V), crystallizes in the monoclinic space group P21/c with two independent molecules in the asymmetric unit, while the second, C23H27Cl2NS, (IX), crystallizes in the orthorhombic space group Pbca with one molecule in the asymmetric unit. In both crystal structures, the 1,3-thiazolidine ring adopts a half-chair conformation. The crystal structures are stabilized by weak C,H,O and C,H,Cl hydrogen bonds in (V) and (IX), respectively. [source]

The fungal metabolite austdiol

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2003
Leonardo Lo Presti
The title compound, (7R,8S)-7,8-dihydroxy-3,7-dimethyl-6-oxo-7,8-dihydro-6H -isochromene-5-carbaldehyde, C12H12O5, is a trans -vicinal diol. Of the two fused rings, which lie approximately in the same plane, the pyran ring is almost perfectly planar, while the cyclohexenone ring adopts a slightly distorted half-chair conformation. The crystal packing is dictated by two strong intermolecular O,H,O interactions, one involving hydroxy and keto groups, the other involving two hydroxy groups. Molecules are linked together through twofold axes, forming zigzag ribbons extended along the a 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]

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]

5,5,-Di- tert -butyl-2,2,-dihydroxy-3,3,-methylenedibenzaldehyde and 6,6,-di- tert -butyl-8,8,-methylenebis(spiro[4H -1,3-benzodioxin-2,1,-cyclohexane])

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2004
Bernardo Masci
Two related compounds containing p - tert -butyl- o -methylene-linked phenol or phenol-derived subunits are described, namely 5,5,-di- tert -butyl-2,2,-dihydroxy-3,3,-methylenedibenzaldehyde, C23H28O4, (I), and 6,6,-di- tert -butyl-8,8,-methylenebis(spiro[4H -1,3-benzodioxin-2,1,-cyclohexane]), C35H48O4, (II). Both compounds adopt a `butterfly' shape, with the two phenol or phenol-derived O atoms in distal positions. Phenol and aldehyde groups in (I) are involved in intramolecular hydrogen bonds and the two dioxin rings in (II) are in distorted half-chair conformations. [source]