3(5),4-Dimethyl- and 3,4,5-trimethylpyrazole at 200 K. X-ray crystallography and quantum-chemical analysis

1999 ◽  
Vol 55 (3) ◽  
pp. 441-447 ◽  
Author(s):  
Lourdes Infantes ◽  
Concepción Foces-Foces ◽  
Jose Elguero
Keyword(s):  
Quantum Chemical ◽  
Molecular Structures ◽  
Asymmetric Unit ◽  
Quantum Chemical Analysis ◽  
X Ray ◽  
X Ray Crystallography ◽  
Crystal And Molecular Structures ◽  
Unit Form ◽  
Proton Disorder ◽  
Independent Molecules

The crystal and molecular structures of 3(5),4-dimethylpyrazole, C5H8N2, (I), and of 3,4,5-trimethylpyrazole, C6H10N2, (II), have been determined at 200 K. In (I) the 4,5-dimethylpyrazole tautomer is present in the solid state and the six independent molecules in the asymmetric unit form trimers via NH...N hydrogen bonds related by a pseudo centre of symmetry. The asymmetric unit of (II) contains one and a half molecules: these exhibit NH proton disorder and are hydrogen bonded to each other via their respective NH groups to form chains. Ab initio calculations at HF and B3LYP/6-31G** levels indicate that the 3,4-dimethylpyrazole tautomer is more stable than the 4,5-dimethylpyrazole tautomer by only approximately 0.5  kcal  mol−1 (1 kcal mol−1 = 4.184 kJ mol−1).

Syntheses, Crystal Structures and Electrochemical Properties of Acetylacetonato-Ruthenium Complexes Containing Substituted Pyridine Ligands

2013 ◽  
Vol 68 (9) ◽  
pp. 993-999 ◽  
Author(s):  
Xiuli Wu ◽  
Rufei Ye ◽  
Ai-Quan Jia ◽  
Qun Chen ◽  
Qian-Feng Zhang
Keyword(s):  
Electrochemical Properties ◽  
Crystal Structures ◽  
Zinc Dust ◽  
Ruthenium Complexes ◽  
Reducing Agent ◽  
Molecular Structures ◽  
X Ray ◽  
X Ray Crystallography ◽  
Crystal And Molecular Structures ◽  
Pyridine Ligands

Treatment of Ru(acac)3 with 2-cyano-pyridine and 3,5-dimethyl-pyridine in the presence of zinc dust as reducing agent in refluxing THF afforded the ruthenium(II) complexes cis-[RuII(acac)2(2- CN-py)2] (1) and cis-[RuII(acac)2(3,5-Me2-py)2] (2), respectively. Interaction of Ru(acac)3 with 3- Me-pyridine and 3,5-Me2-pyridine in the presence of Br2 in refluxing THF gave the ruthenium(III) complexes [RuIII(acac)Br2(3-Me-py)2] (3) and [RuIII(acac)Br2(3,5-Me2-py)2] (4), respectively. The four complexes have been spectroscopically and electrochemically characterized, and their crystal and molecular structures have been established by X-ray crystallography

Synthese Und Kristallstrukturen Von Chlorometallaten [M = V(III), Mo(V)]

2001 ◽  
Vol 56 (8) ◽  
pp. 759-764 ◽  
Author(s):  
Soheila Chitsaz ◽  
Effat Iravani ◽  
Jochen Pauls ◽  
Bernhard Neumüller
Keyword(s):  
Ir Spectroscopy ◽  
Membered Ring ◽  
Dinuclear Complex ◽  
Monoclinic Space Group ◽  
Asymmetric Unit ◽  
Space Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Independent Molecules ◽  
Triclinic Form

[(THF)2LiCl2VCl2(THF)2] (1) and [Li(THF)4][OMoCl4(THF)] (2) can be prepared by the reactions of VCI3 with LiCl in THF and of Li(H)PtBu with OM0 CI4 in THF, respectively. 1 and 2 were characterized by IR spectroscopy, MS spectrometry (2) and X-ray crystallography. 1 can be obtained in two modifications depending on the temperature of crystallization. At -30 °C a triclinic form, 1a, was isolated from THF solution with one unique molecule per asymmetric unit. However, at 20 °C, 1b crystallized in the monoclinic space group P2/c. It possesses four independent molecules per asymmetric unit. According to the structure analyses 1 consists of a dinuclear complex with a planar LiCl2V four-membered ring while 2 consists of seperate ions [Li(THF)4]+ and [OMoCl4(THF)]-

Influence of fluorine substitution on the molecular conformation of 3′-deoxy-3′-fluoro-5-methyluridine

2020 ◽  
Vol 76 (4) ◽  
pp. 346-352
Author(s):  
Manisha N. Aher ◽  
Namrata D. Erande ◽  
Vaijayanti A. Kumar ◽  
Moneesha Fernandes ◽  
Rajesh G. Gonnade
Keyword(s):  
Molecular Conformation ◽  
Asymmetric Unit ◽  
Screw Axis ◽  
Orthorhombic Space Group ◽  
Fluorine Substitution ◽  
X Ray ◽  
X Ray Crystallography ◽  
Conformational Properties ◽  
Independent Molecules ◽  
Phase Angles

Fluorine substitutions on the furanose ring of nucleosides are known to strongly influence the conformational properties of oligonucleotides. In order to assess the effect of fluorine on the conformation of 3′-deoxy-3′-fluoro-5-methyluridine (RTF), C10H13FN2O5, we studied its stereochemistry in the crystalline state using X-ray crystallography. The compound crystallizes in the chiral orthorhombic space group P212121 and contains two symmetry-independent molecules (A and B) in the asymmetric unit. The furanose ring in molecules A and B adopts conformations between envelope (2E, 2′-endo, P = 162°) and twisted (2T3, 2′-endo and 3′exo, P = 180°), with pseudorotation phase angles (P) of 164.3 and 170.2°, respectively. The maximum puckering amplitudes, νmax, for molecules A and B are 38.8 and 36.1°, respectively. In contrast, for 5-methyluridine (RTOH), the value of P is 21.2°, which is between the 3E (3′-endo, P = 18.0°) and 3T4 (3′-endo and 4′-exo, P = 36°) conformations. The value of νmax for RTOH is 41.29°. Molecules A and B of RTF generate respective helical assemblies across the crystallographic 21-screw axis through classical N—H...O aand O—H...O hydrogen bonds supplemented by C—H...O contacts. Adjacent parallel helices of both molecules are linked to each other via O—H...O and O...π interactions.

Crystal and molecular structures of three 2-substituted 4-methyloxan-4-ol derivatives studied by X-ray crystallography and by PM6 calculations

2008 ◽  
Vol 223 (7/2008) ◽  
Author(s):  
Julio Zukerman-Schpector ◽  
Alcindo A. Dos Santos ◽  
Alexandra Macedo ◽  
Edison P. Wendler ◽  
Gilmar A. Brito ◽  
...  
Keyword(s):  
Single Crystal ◽  
Molecular Structures ◽  
X Ray ◽  
X Ray Crystallography ◽  
Crystal And Molecular Structures ◽  
Semi Empirical

AbstractThe conformational features of three 2-substituted 4-methyloxan-4-ol (tetrahydropyran) derivatives were investigated by single crystal X-ray crystallographic studies and the geometries were optimized using semi-empirical PM6 methods. The tetrahydropyran ring in each of (

scholarly journals Crystal structure of 3,4a,7,7,10a-pentamethyl-3-vinyldodecahydro-1H-benzo[f]chromen-9-ol isolated fromSideritis perfoliata

2016 ◽  
Vol 72 (10) ◽  
pp. 1380-1382 ◽  
Author(s):  
Ísmail Çelik ◽  
Cem Cüneyt Ersanlı ◽  
Rahmi Köseoğlu ◽  
Hüseyin Akşit ◽  
Ramazan Erenler ◽  
...  
Keyword(s):  
Quantum Chemical ◽  
Chair Conformation ◽  
Van Der Waals Interactions ◽  
Asymmetric Unit ◽  
Screw Axis ◽  
X Ray ◽  
Compound C ◽  
Independent Molecules ◽  
Semi Empirical ◽  
Absolute Structure

The asymmetric unit of the title compound, C20H34O2, contains two crystallographically independent molecules (1 and 2) with similar conformations. In both molecules, the cyclohexane rings adopt a chair conformation, while the oxane rings are also puckered. In the crystal, O—H...O hydrogen bonds connect adjacent molecules, formingC(6) helical chains located around a 21screw axis and running along the crystallographicaaxis. The packing of these chains is governed only by van der Waals interactions. Semi-empiricalPM3quantum chemical calculations are in a satisfactory agreement with the structural results of the X-ray structure analysis. The absolute structure was indeterminate in the present experiment.

Crystal and Molecular Structures of Penta-O-acetyl-aldehydo-D-glucose Dimethyl Acetal and of Hepta-O-acetyl-aldehydo-D-glucose Hydrate

1996 ◽  
Vol 49 (3) ◽  
pp. 391 ◽  
Author(s):  
P Koll ◽  
J Kopf
Keyword(s):  
Solid State ◽  
Single Crystal ◽  
Dimethyl Acetal ◽  
Molecular Structures ◽  
Carbon Skeleton ◽  
Parallel Orientation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Crystal And Molecular Structures ◽  
Solid State Structures

The solid-state structures of the title compounds were determined by conventional single-crystal X-ray crystallography. In both cases a planar zigzag conformation of the carbon skeleton is observed with a resulting 1,3-parallel orientation of O(2) and O(4). In the case of the heptaacetate even a second such arrangement is established between O(3) and one of the oxygens at C(1). These findings substantiate the claim that such conformations are not as unfavourable as previously was assumed by many authors.

Convenient synthesis, X-ray crystal structure, and Raman spectrum of the heptasulphide dianion, S72−, in [PPN]2S7•2EtOH

1986 ◽  
Vol 64 (8) ◽  
pp. 1509-1513 ◽  
Author(s):  
Tristram Chivers ◽  
Frank Edelmann ◽  
John F. Richardson ◽  
Kenneth J. Schmidt
Keyword(s):  
Crystal Structure ◽  
Raman Spectrum ◽  
Molecular Structures ◽  
High Yield ◽  
Torsion Angles ◽  
X Ray ◽  
X Ray Crystallography ◽  
Crystal And Molecular Structures ◽  
Convenient Synthesis ◽  
Stretching Vibrations

The S72− ion is readily prepared in high yield by the reaction of [PPN]SH with cyclo-S8 in ethanol. The crystal and molecular structures of [PPN]2S7•2EtOH have been determined by X-ray crystallography. The crystals are monoclinic and belong to the space group P21, a = 13.199(2), b = 19.414(2), c = 14.046(2) Å, β = 94.027(6)°, V = 3590.3(7) Å3, Z = 2. The final R and Rw values were 0.064 and 0.060, respectively. The S72− ion is an unbranched chain of sulphur atoms in the cis,trans,cis-configuration with torsion angles of 89.99(18), 71.84(16), 76.54(16), and 94.19(18)°. The S—S distances (in Å) become progressively smaller in the sequence d(S—S central) [2.072(3) and 2.070(3)] > d(S—S internal) [2.050(2) and 2.037(3)] > d(S—S) terminal [2.044(3) and 2.026(4)]. The Raman spectrum of the S72− ion in [PPN]2S7•2EtOH exhibits characteristic S—S stretching vibrations at 503, 453, 419, and 395 cm−1.

Structure of Z-(Aib)9OBu t

1998 ◽  
Vol 54 (3) ◽  
pp. 300-307 ◽  
Author(s):  
R. Geßmann ◽  
H. Brückner ◽  
M. Kokkinidis
Keyword(s):  
Title Compound ◽  
The Other ◽  
Asymmetric Unit ◽  
X Ray ◽  
Aminoisobutyric Acid ◽  
X Ray Crystallography ◽  
C Terminus ◽  
Independent Molecules ◽  
Intramolecular Hydrogen ◽  
Layer Chromatography

The structure of the synthetic protected oligopeptide Z-(Aib)9OBu t , tert-butoxynona(α-aminoisobutyric acid), which contains the unusual α-aminoisobutyric acid (Aib), was determined by X-ray crystallography. The two independent molecules in the asymmetric unit fold into 310-helices, each stabilized by seven intramolecular hydrogen bonds. The C terminus of one of the molecules is disordered and adopts a semi-extended conformation, which is rather unusual for Aib residues. This is the first observation of such a conformation involved in a disorder in Aib-containing oligopeptides. The existence of a second conformation for the C-terminal residue might explain the difficulties in crystallizing the title compound and a different behaviour of the title compound in thin layer chromatography compared with the other homopeptides.

scholarly journals Die Kristall- und Molekülstrukturen der Verbindungen [Cl4–xSn{Co(CO)4}x] mit x = 1,2 und 3 / The Crystal and Molecular Structures of the Compounds [Cl4-xSn{Co(CO)4}x] with x = 1,2 and 3

1991 ◽  
Vol 46 (2) ◽  
pp. 187-191 ◽  
Author(s):  
Peter Klüfers
Keyword(s):  
Crystal Structures ◽  
Molecular Structures ◽  
Trigonal Bipyramid ◽  
X Ray ◽  
X Ray Crystallography ◽  
Crystal And Molecular Structures ◽  
Distorted Trigonal Bipyramid

The crystal structures of the compounds [Cl3SnCo(CO)4] 1, [Cl2Sn{Co(CO)4}2]2, and [ClSn{Co(CO)4}3]3, have been determined by X-ray crystallography. Sn is co-ordinated tetrahedrally by Cl- and Co-substituents, the co-ordination polyhedron of Co is a distorted trigonal bipyramid. The Sn -Cl- and the Sn-Co-distances both increase from 1 to 3 (Sn -Co: 247.7 in 1, 253.2 in 2, and 260.6 pm in 3).

Sign in / Sign up

Export Citation Format

Share Document