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Cycloaddition of trifluoromethyl azafulvenium methides: synthesis of new triflu...
Nunes, Cláudio M.; Silva, Manuela Ramos; Beja, Ana Matos; Fausto, Rui; Melo, Teresa M.V.D. Pinho eThe chemistry of trifluoromethyl azafulvenium methides was explored leading to a new route to trifluoromethylpyrrole-annulated systems. The first evidence of azafulvenium methides acting as 1,3-dipoles is reported. These azafulvenium methides showed site selectivity in the reaction with strong electron-deficient dipolarophiles leading exclusively to 1,3-cycloadducts. In the cycloaddition with less-activated dip...
3-Oxoandrosta-4,6-dien-17[beta]-yl 2-methyl-1H-imidazole-1-carboxylate and 3-ox...
Silva, Manuela Ramos; Moreira, Vânia M.; Cardoso, Cláudia; Beja, Ana Matos; Salvador, Jorge A. R.The title compounds, C24H30N2O3, (I), and C24H34N2O3, (II), both contain an androstane backbone and a 2-methylimidazole-1-carboxylate moiety at the 17-position. Compound (I) contains two symmetry-independent molecules (denoted 1 and 2), while compound (II) contains just one molecule in the asymmetric unit. The C-C-O-C torsion angle that reflects the twisting of the 2-methylimidazole-1-carboxylate moiety from th...
Conformation of 17-chloro-16-formylandrosta-5,16-dien-3[beta]-yl acetate and 17...
Silva, Manuela Ramos; Moreira, Vânia M.; Cardoso, Cláudia; Beja, Ana Matos; Salvador, Jorge A. R.In the title compounds, C22H29ClO3, (I), and C21H29ClO2, (II), respectively, the B rings adopt a half-chair conformation and the D rings adopt an envelope conformation. A twist of the steroid skeleton of both compounds is observed. There is a positional disorder of the acetoxy group of (II), with the terminal atoms disordered over two positions with near equal occupancy. Quantum-mechanical ab initio calculation...
Propeller-like Conformation of Diphenylacetic Acid
Silva, Manuela; Cardoso, Cláudia; Beja, Ana; Paixão, José; Domingos, SérgioAbstract Crystal structure of diphenylacetic acid has been solved by X-ray diffraction. The crystals are monoclinic, space group P21/c, with a = 12.254(4) Å, b = 7.2260(8) Å, c = 17.521(4) Å, ß = 133.38(1)°, Mr = 212.24, V = 1127.6(5) Å3, Z = 4 and R = 0.045. A strong hydrogen bond links the molecules in dimers. The dimers are connected by weaker C–H···p and p···p interactions. A calculation was performed for ...
X-ray Diffraction and DFT Studies of 2-Methoxy-5-phenylaniline
Marques, Ana; Silva, Joana; Silva, Manuela; Beja, Ana; Justino, Licinia; Sobral, AbilioAbstract 2-Methoxy-5-phenylaniline, a promissor monomer for PANI studies, has been characterized by single-crystal X-ray diffraction at two temperatures: orthorhombic, space group P212121, Z = 12 with a = 5.9900(2) Å, b = 20.4873(6) Å, c = 26.3727(8) Å and R = 0.0868 for 293(2) K and a = 5.8337(9) Å, b = 20.4428(31) Å, c = 26.0773(40) Å and R = 0.0669 for 120(2) K. There are three independent molecules in the ...
C–H···p and C=O···p Intermolecular Interactions in Dibenzyl-3,6-dimethylpyrazin...
Silva, Joana; Santos, Ana; Marques, Ana; Silva, Manuela; Beja, Ana; Sobral, AbílioAbstract A new pyrazine compound, has been synthesised and characterised by single-crystal X-ray diffraction: monoclinic, P21/c with a = 11.0707(3) Å, b = 5.23700(10) Å, c = 16.6997(5) Å, ß = 103.5385(16)°, Mr = 376.40, V = 941.30(4) Å3, Z = 2. Each molecule possesses C i symmetry with the two halves of the molecule related by an inversion centre. C–H···p and C=O···p interactions held the molecules together....
Chemistry of Diazafulvenium Methides in the Synthesis of Functionalized Pyrazoles
Melo, Teresa M. V. D. Pinho e; Nunes, Cláudio M.; Soares, Maria I. L.; Paixão, José A.; Beja, Ana Matos; Silva, Manuela RamosThe chemistry of diazafulvenium methides generated by the thermal extrusion of sulfur dioxide from 2,2-dioxo-1H,3H-pyrazolo[1,5-c] [1,3]thiazoles is described. The diazafulvenium methides unsubstituted at C-7 participate in [8π + 2π] cycloadditions giving pyrazolo-annulated heterocycles resulting from the addition across the 1,7-position. 1-Methyl-diazafulvenium methides and 7,7-dimethyl-diazafulvenium methides...
A ladder type structure: Rubidium diphenylacetate diphenylacetic acid
Silva, Manuela; Beja, Ana; Paixão, José A.; Domingos, Sérgio R.; Martín-Gil, JesúsA new rubidium complex, rubidium diphenylacetate diphenylacetic acid has been synthesised and characterised by single-crystal X-ray diffraction: triclinic, P $$\bar1$$ with a=7.437(3) , b=12.377(4) , c=14.384(3) , a=107.08(2), ß=103.67(2), ?=96.95(3), Mr=508.93, V=1203.6(6) 3, Z=2. The diphenylacetic molecules bridge the metallic ions forming an infinite ladder structure. Two strong hydrogen bonds link the orga...
Synthesis, crystal structure and magnetic properties of an alternating manganes...
Silva, Manuela Ramos; Beja, Ana Matos; Paixão, José António; Martín-Gil, JesusA new 1D complex has been prepared and characterized. X-ray single crystal structure confirms that the Mn(II) ions assemble in alternating chains with Mn-Mn distances of 3.8432(13) and 4.4428(14) Å. A 3D network of hydrogen bonds links the chains together. The temperature dependence of the magnetic susceptibility reveals that this compound undergoes a magnetic transition and exhibits an antiferromagnetic intera...
Crystal structure and properties of l-tryptophanium hydrogen selenite
Paixão, José António; Silva, Manuela Ramos; Beja, Ana Matos; Eusébio, Ermelindal-Tryptophanium hydrogen selenite was synthesised and structurally characterised at room and low temperature. The aminoacid is positively charged with the amine and carboxylic group protonated. It adopts a staggered conformation with the N1 gauche to C4 that is gauche to C1. The anion displays a pyramidal conformation with three different Se-O bond lengths, one characteristic of a double bond, another of a sing...
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