Tautomerism troubles: proton transfer modifies the stereochemical assignments in diastereoisomeric structures of spirocyclic 5-methyl-2H-imidazol-4-amine dimers

During the racemization of a novel pharmaceutical spirocyclic imidazole–amine compound, namely, 6′-bromo-N-(6′-bromo-4-methoxy-4′′-methyl-3′H-dispiro[cyclohexane-1,2′-indene-1′,2′′-imidazol]-5′′-yl)-4-methoxy-4′′-methyl-3′H-dispiro[cyclohexane-1,2′-indene-1′,2′′-imidazol]-5′′-imine, C36H41Br2N5O2, two impurities were isolated. These impurities were clearly dimers from mass spectroscopic analysis, however single-crystal diffraction characterization was required for the assignment of stereochemistry. The single-crystal diffraction results revealed subtly different structures to those proposed, due to an unexpected proton transfer. The dimers contain four stereocentres, but two of primary interest, and are centrosymmetric, so after careful structure refinement and close inspection it was possible to unambiguously assign the stereochemistry of both the homochiral [(S),(S)- and (R),(R)-] and the heterochiral [(S),(R)- and (R),(S)-] compounds.

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Crystal structure refinement of MgSiO3high temperature C2/c clinoenstatite

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273314099203 ◽

2014 ◽

Vol 70 (a1) ◽

pp. C79-C79

Author(s):

Akira Yoshiasa ◽

Akihiko Nakatsuka ◽

Maki Okube ◽

Tomoo Katsura

Keyword(s):

High Temperature ◽

Single Crystal ◽

Structure Refinement ◽

Ambient Conditions ◽

X Ray Diffraction ◽

Temperature Quenching ◽

Single Crystal Diffraction ◽

X Ray ◽

Metastable Structure ◽

Rapid Pressure

The high-temperature clinoenstatite (HT-CEn) is one of the important MgSiO3 pyroxene polymorph. The single-crystal of C2/c HT-CEn endmember is firstly synthesized by rapid pressure-temperature quenching from 15-16 GPa and 900-19000C [1]. No report that it is produced as single crystal or large domain has been made on the MgSiO3 endmember. The HT-CEn-type modifications are observed in Ca-poor Mg-Fe clinoenstatite and pigeonite and are always found to be unquenchable in rapid cooling. The high pressure and high temperature experiments of MgSiO3 composition were carried out with a Kawai-type multi-anvil apparatus. The samples were quenched by rapidly releasing the oil pressure load and/or by blow out of anvil cell gasket. The space group of C2/c is strictly determined by Rigaku RAPID Weissenberg photographs and synchrotron radiation. Single-crystal X-ray diffraction experiments were performed at ambient conditions using a Rigaku AFC-5 four circle diffractometer. A total of 9383 reflections was measured and averaged in Laue symmetry 2/m to give 766 independent reflections used for the structure refinements. Final reliability factors converged smoothly to R = 0.029. The single-crystal diffraction analysis shows that the unusual bonding distances frozen in this metastable structure. The degree of kinking of the silicate tetrahedral chains is 1750for HT-CEn. The chain angle for HP-CEn is substantially smaller (1350) and the angle for L-CEn turned to the opposite direction at -1600(=2000). The degree of kinking increases by being curved in more than 1800in the transition from HT-CEn to L-CEn. As for the reverse change from the expansion to the stretch, a potential barrier exists in the point of the continuity. It is suggested that the reason which can quench structure under ambient conditions is the present HT-CEn single crystal was formed by the isosymmetric phase transition from HP-CEn. HT-CEn type single-crystals cannot be frozen without pressure.

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Ludwigite from central Sweden: new data and crystal structure refinement

Mineralogical Magazine ◽

10.1180/002646199548682 ◽

1999 ◽

Vol 63 (4) ◽

pp. 511-518 ◽

Cited By ~ 4

Author(s):

P. W. U. Appel ◽

M. F. Brigatti

Keyword(s):

Crystal Structure ◽

Single Crystal ◽

Coastal Area ◽

Structure Refinement ◽

Iron Ores ◽

Crystal Structure Refinement ◽

Single Crystal Diffraction ◽

Distortion Parameter ◽

Area North ◽

Site Population

AbstractLudwigite from B-bearing iron ores in the Bergslagen area of central Sweden and in the coastal area north of Stockholm has been studied using chemical and single-crystal diffraction techniques. Structure refinements, completed for three crystals showing slightly different Al contents, in the space group Pbam (agreement factor: 2.42 ≤ R ≤ 2.79) indicate that: (1) octahedral M1, M2 and M3 bond distances are similar, although the calculated site population suggests that M1 and M2 are nearly completely occupied by Mg whereas M3 also contains Fe2+ and Fe3+; (2) in the M4 octahedron Fe3+ and Al dominate over Mg (and Fe2+); and (3) the distortion parameter, BLD, indicates that M3 is the most regular, whereas M4 is the most distorted octahedron.

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Single-crystal structure refinement of four compounds in the Y1−xPrxBa2Cu3−yAlyO7−δ system

Journal of Materials Research ◽

10.1557/jmr.1996.0381 ◽

1996 ◽

Vol 11 (12) ◽

pp. 3000-3004 ◽

Cited By ~ 3

Author(s):

A. Meden ◽

E. Holzinger-Schweiger ◽

G. Leising ◽

S. Pejovnik ◽

L. Golič

Keyword(s):

Single Crystal ◽

Structure Refinement ◽

Structural Effect ◽

The Self ◽

Tetragonal Symmetry ◽

Structural Refinement ◽

Flux Method ◽

Single Crystal Diffraction ◽

X Ray ◽

Wet Chemical

X-ray single crystal diffraction data were used for structural refinement of the title compounds with different x (0.15, 0.27, 0.49, and 0.89). Crystals were grown in alumina crucibles using the self-flux method. Aluminum, which originates from the crucibles, substitutes only Cu(1), and thus induces tetragonal symmetry which was observed in all four crystals. The main structural effect of praseodymium is an increased separation of superconducting layers. Substituent concentrations (x and y in the formula) have been refined and compared with the values obtained by EDX (energy dispersive x-ray analysis) in an electron microscope. It was indicated that the refined values of Y: Pr ratio and the oxygen content are more reliable than those obtained by EDX while the refinement is less sensitive for Cu(1): Al ratio, and this value is more uncertain. This is in accordance with the result of wet chemical analysis.

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Ba-rich celestine: new data and crystal structure refinement

Mineralogical Magazine ◽

10.1180/minmag.1997.061.406.10 ◽

1997 ◽

Vol 61 (406) ◽

pp. 447-451 ◽

Cited By ~ 9

Author(s):

M. F. Brigatti ◽

E. Galli ◽

L. Medici

Keyword(s):

Single Crystal ◽

Structure Refinement ◽

Chemical Analyses ◽

Unit Cell Parameters ◽

Single Crystal Diffraction ◽

X Ray ◽

Cell Parameters ◽

Individual Bond ◽

Oxygen Bond

AbstractA Ba-rich celestine (Sr0.87Ba0.13SO4) filling cavities of volcanoclastic rocks from Montecchio Maggiore (Vicenza, Italy) was studied. The role of the Ba content in the mineral was determined using X-ray powder data, single crystal X-ray refinement, thermal and chemical analyses. The unit cell parameters (obtained by single crystal diffraction) are a = 8.408, b = 5.372, c = 6.897 Å, and the refinement in the space group Pnma (Z = 4) gives the final R value of 0.039. The average (Sr,Ba)-oxygen bond length is 2.842 Å and agrees with an occupancy of Sr 87% and Ba 13%. Individual bond lengths (Sr,Ba)-O and bond strength calculations confirm that all twelve interactions are significant and define an irregular array around the cation.

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A vacuum chamber for low background diffraction experiments

Zeitschrift für Kristallographie - Crystalline Materials ◽

10.1524/zkri.1996.211.9.591 ◽

1996 ◽

Vol 211 (9) ◽

Cited By ~ 1

Author(s):

R. B. Neder ◽

M. Burghammer ◽

Th. Grasl ◽

H. Schulz

Keyword(s):

Single Crystal ◽

Vacuum Chamber ◽

Single Crystal Diffraction ◽

Low Background

AbstractWe developed a small vacuum chamber for very low background single crystal diffraction experiments. The chamber has been designed for a large Eulerian cradle. The

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Combined high resolution powder and single-crystal diffraction to determine the structure of Li1+xCeIIIxCeIV6-xF25

Zeitschrift für Kristallographie Supplements ◽

10.1524/zksu.2007.2007.suppl_26.455 ◽

2007 ◽

Vol 2007 (suppl_26) ◽

pp. 455-460 ◽

Cited By ~ 1

Author(s):

G. Renaudin ◽

E. Mapemba ◽

M. El-Ghozzi ◽

M. Dubois ◽

D. Avignant ◽

...

Keyword(s):

High Resolution ◽

Single Crystal ◽

Single Crystal Diffraction

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Iron in kornerupine; a57Fe Moessbauer spectroscopic study and comparison with single-crystal structure refinement

American Mineralogist ◽

10.2138/am-1999-0407 ◽

1999 ◽

Vol 84 (4) ◽

pp. 536-549 ◽

Cited By ~ 5

Author(s):

Edward S. Grew ◽

Guenther J. Redhammer ◽

Georg Amthauer ◽

Mark A. Cooper ◽

Frank C. Hawthorne ◽

...

Keyword(s):

Crystal Structure ◽

Single Crystal ◽

Spectroscopic Study ◽

Structure Refinement ◽

Single Crystal Structure ◽

Crystal Structure Refinement

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Environmentally Friendly Nafion-Catalyzed Synthesis of Substituted 2-Ethyl-3-Methylquinolines from Aniline and Propionaldehyde under Microwave Irradiation

Catalysts ◽

10.3390/catal11080877 ◽

2021 ◽

Vol 11 (8) ◽

pp. 877

Author(s):

Chieh-Kai Chan ◽

Chien-Yu Lai ◽

Cheng-Chung Wang

Keyword(s):

Reaction Mechanism ◽

Microwave Irradiation ◽

Single Crystal ◽

Diffraction Analysis ◽

Environmentally Friendly ◽

Single Crystal Diffraction ◽

X Ray ◽

Related Data ◽

Heating Source ◽

Chemical Structures

Herein, we report a facile synthetic methodology for the preparation of 2,3-dialkylquinolines from anilines and propionaldehydes. This cyclization involved environmentally friendly Nafion® NR50 as an acidic catalyst with microwave irradiation as the heating source. A series of substituted 2-ethyl-3-methylquinolines were prepared from various anilines and propionaldehyde derivatives through this protocol with good to excellent yields. Some new chemical structures were confirmed by X-ray single-crystal diffraction analysis and the related data were provided. The plausible reaction mechanism studies are also discussed.

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