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Ring Plane (ring + plane)

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Chemistry100%

Selected Abstracts

Bromido(,5 -carboxycyclopentadienyl)dinitrosylchromium(0) and (,5 -benzoylcyclopentadienyl)bromidodinitrosylchromium(0)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009
Yu-Pin Wang
In the structures of each of the title compounds, [CrBr(C6H5O2)(NO)2], (I), and [CrBr(C12H9O)(NO)2], (II), one of the nitrosyl groups is located at a site away from the exocyclic carbonyl C atom of the cyclopentadienyl (Cp) ring, with twist angles of 174.5,(3) and 172.5,(1)°. The observed orientation is surprising, since the NO group is expected to be situated trans to an electron-rich C atom in the ring. The organic carbonyl plane is turned away from the Cp ring plane by 5.6,(8) and 15.2,(3)°in (I) and (II), respectively. The exocyclic C,C bond in (I) is bent out of the Cp ring plane towards the Cr atom by 2.8,(3)°, but is coplanar with the Cp ring in (II); the angle is 0.1,(1)°. [source]

Halide salts of antimigraine agents eletriptan and naratriptan

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2008
K. Ravikumar
Molecules of eletriptan hydrobromide monohydrate (systematic name: (1S,2R)-1-methyl-2-{5-[2-(phenylsulfonyl)ethyl]-1H -indol-3-ylmethyl}pyrrolidinium bromide monohydrate), C22H27N2O2S+·Br,·H2O, (I), and naratriptan hydrochloride (systematic name: 1-methyl-4-{5-[2-(methylsulfamoyl)ethyl]-1H -indol-3-yl}piperidinium chloride), C17H26N3O2S+·Cl,, (II), adopt conformations similar to other triptans. The C-2 and C-5 substituents of the indole ring, both of which are in a region of conformational flexibility, are found to be oriented on either side of the indole ring plane in (I), whilst they are on the same side in (II). The N atom in the C-2 side chain is protonated in both structures and is involved in the hydrogen-bonding networks. In (I), the water molecules create helical hydrogen-bonded chains along the c axis. In (II), the hydrogen bonding of the chloride ions results in macrocyclic R42(20) and R42(24) ring motifs that form sheets in the bc plane. This structural analysis provides an insight into the molecular structure,activity relationships within this class of compound, which is of use for drug development. [source]

trans -Bis[1-benzyl-3-(2,3,4,5,6-penta­fluoro­benz­yl)benzimidazol-2-yl­idene]­dibromo­palladium(II)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2006
Aytaç Gürhan Gökçe
The title compound, [PdBr2(C21H13F5N2)2], crystallizes with two independent centrosymmetric conformational isomers having a square-planar coordination at the Pd atom. The conformational isomers differ by the ligands having a cis or trans orientation of their benzyl and pentafluorobenzyl rings with respect to the benzimidazole ring plane. The benzimidazole rings are rotated with respect to the coordination plane of the metal by 79.1,(2) and 75.2,(1)° for mol­ecules A and B, respectively. The Pd,Br bond lengths are 2.4218,(8) and 2.4407,(10),Å for mol­ecules A and B, respectively, and the Pd,C bond lengths are 2.030,(8) and 2.018,(9),Å. The crystal structure contains two types of C,H,F and one type of C,H,Br intra­molecular contact, as well as C,H,, inter­actions. [source]

Poly­[copper(II)-,-pyrazine-,3 -squarato]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2001
Christian Näther
In the structure of the title compound, [Cu(C4O4)(C4H4N2)]n, each copper cation is surrounded by three squarate (3,4-di­hydroxy-3-cyclo­butene-1,2-dioate) anions and two pyrazine ligands, all of which are located in special positions. The copper cation and all atoms of the squarate anion are located on a mirror plane, whereas the pyrazine ligand is located around a mirror plane which is perpendicular to the ring plane. The cations are connected via the squarate anions and the pyrazine ligands, forming sheets parallel to (001). [source]

Cyclic ,-Tetra- and Pentapeptides: Synthesis through On-Resin Cyclization and Conformational Studies by X-Ray, NMR and CD Spectroscopy and Theoretical Calculations

CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005
Frank Büttner Dr.
Abstract The solution-phase synthesis of the simplest cyclic ,-tetrapeptide, cyclo(,-Ala)4 (4), as well as the solid-phase syntheses through side chain anchoring and on-resin cyclization of the cyclic ,3 -tetrapeptide cyclo(-,3hPhe-,3hLeu-,3hLys-,3hGln-) (14) and the first cyclic ,3 -pentapeptide cyclo(-,3hVal-,3hPhe-,3hLeu-,3hLys-,3hLys-) (19) are reported. Extensive computational as well as spectroscopic studies, including X-ray and NMR spectroscopy, were undertaken to determine the preferred conformations of these unnatural oligomers in solution and in the solid state. cyclo(,-Ala)4 (4) with no chiral side chains is shown to exist as a mixture of rapidly interchanging conformers in solution, whereas inclusion of chiral side chains in the cyclo-,3 -tetrapeptide causes stabilization of one dominating conformer. The cyclic ,3 -pentapeptide on the other hand shows larger conformational freedom. The X-ray structure of achiral cyclo(,-Ala)4 (4) displays a Ci -symmetrical 16-membered ring with adjacent CO and N-H atoms pointing pair wise up and down with respect to the ring plane. CD spectroscopic examinations of all cyclic ,-peptides were undertaken and revealed results valuable as starting point for further structural investigations of these entities. [source]

Reaction Mechanism of Porphyrin Metallation Studied by Theoretical Methods

CHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2005
Yong Shen Dr.
Abstract We have studied the reaction mechanism for the insertion of Mg2+ and Fe2+ into a porphyrin ring with density functional calculations with large basis set and including solvation, zero-point and thermal effects. We have followed the reaction from the outer-sphere complex, in which the metal is coordinated with six water molecules and the porphyrin is doubly protonated, until the metal ion is inserted into the deprotonated porphyrin ring with only one water ligand remaining. This reaction involves the stepwise displacement of five water molecules and the removal of two protons from the porphyrin ring. In addition, a step seems to be necessary in which a porphyrin pyrrolenine nitrogen atom changes its interaction from a hydrogen bond to a metal-bound solvent molecule to a direct coordination to the metal ion. If the protons are taken up by a neutral imidazole molecule, the deprotonation reactions are exothermic with minimal barriers. However, with a water molecule as an acceptor, they are endothermic. The ligand exchange reactions were approximately thermoneutral (±20 kJ,mol,1, with one exception) with barriers of up to 72 kJ,mol,1 for Mg and 51 kJ,mol,1 for Fe. For Mg, the highest barrier was found for the formation of the first bond to the porphyrin ring. For Fe, a higher barrier was found for the formation of the second bond to the porphyrin ring, but this barrier is probably lower in solution. No evidence was found for an initial pre-equilibrium between a planar and a distorted porphyrin ring. Instead, the porphyrin becomes more and more distorted as the number of metal,porphyrin bonds increase (by up to 191 kJ,mol,1). This strain is released when the porphyrin becomes deprotonated and the metal moves into the ring plane. Implications of these findings for the chelatase enzymes are discussed. [source]

Reversible phase transition of pyridinium-3-carboxylic acid perchlorate

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010
Heng-Yun Ye
Pyridinium-3-carboxylic acid perchlorate was synthesized and separated as crystals. Differential scanning calorimetry (DSC) measurements show that this compound undergoes a reversible phase transition at ,,135,K with a wide hysteresis of 15,K. Dielectric measurements confirm the transition at ,,127,K. Measurement of the unit-cell parameters versus temperature shows that the values of the c axis and , angle change abruptly and remarkably at 129,(2),K, indicating that the system undergoes a first-order transition at Tc = 129,K. The crystal structures determined at 103 and 298,K are all monoclinic in P21/c, showing that the phase transition is isosymmetric. The crystal contains one-dimensional hydrogen-bonded chains of the pyridinium-3-carboxylic acid cations, which are further linked to perchlorate anions by hydrogen bonds to form well separated infinite planar layers. The most distinct differences between the structures of the higher-temperature phase and the lower-temperature phase are the change of the distance between the adjacent pyridinium ring planes within the hydrogen-bonded chains and the relative displacement between the hydrogen-bonded layers. Structural analysis shows that the driving force of the transition is the reorientation of the pyridinium-3-carboxylic acid cations. The degree of order of the perchlorate anions may be a secondary order parameter. [source]

trans -[1,3-Bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene]dichlorido(triphenylphosphine-,P)palladium(II)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2007
Hayati Türkmen
The title complex, [PdCl2(C21H26N2)(C18H15P)], shows slightly distorted square-planar coordination around the PdII metal centre. The Pd,C bond distance between the N-heterocyclic ligand and the metal atom is 2.028,(5),Å. The dihedral angle between the two trimethylphenyl ring planes is 36.9,(2)°. [source]

(E)-4-(4-Bromo­phenyl­diazen­yl)-2,6-dimethyl­phenyl acrylate and (E)-2,6-dimethyl-4-(4-methyl­phenyl­diazen­yl)­phenyl acrylate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2007
Hasan Kocaokutgen
The crystal structures of the title compounds, C17H15BrN2O2, (I), and C18H18N2O2, (II), determined at room temperature, have a trans configuration with respect to the diazene linkage, as found for other azo (diazene) derivatives. The aromatic mean planes are nearly coplanar, with a dihedral angle between these planes of 8.31,(2)° for (I) and 3.74,(2)° for (II). In both complexes, the mean plane of the ester group is nearly perpendicular to the aromatic ring planes. In both compounds, the crystal packing involves only ,,, and ,,ring inter­actions, which combine to stabilize the extended structure. [source]