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Polarized Electronic Structure (polarized + electronic_structure)
Selected AbstractsAmino-substituted O6 -benzyl-5-nitrosopyrimidines: interplay of molecular, molecular-electronic and supramolecular structuresACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2002Antonio Quesada The structures of eight 2,4,6-trisubstituted-5-nitrosopyrimidines (one of which crystallizes in two polymorphs) have been determined, including seven O6 -benzyl derivatives which are potential, or proven, in vitro inhibitors of the human DNA-repair protein O6 -alkylguanine-DNA-transferase. In the derivatives having an amino substituent at the 4-position, an intramolecular N,H,O hydrogen bond with the nitroso O as an acceptor leads to an overall molecular shape similar to that of substituted purines. There is a marked propensity for these nitroso compounds to crystallize with Z, = 2. The structure of an analogue with no nitroso group is also reported for comparative purposes. Compounds containing the N -alkyl substituents ,NHCH2COOEt, ,NHCH2CH2COOEt and ,NHCH(CH2Ph)COOEt, derived from amino acid esters, exhibit a rich variety of conformational behaviour, and in all of the nitroso compounds the bond lengths provide strong evidence for a highly polarized electronic structure. Associated with this polarization is extensive charge-assisted hydrogen bonding between the molecules, leading to supramolecular aggregation in the form of finite (zero-dimensional) aggregates, chains, molecular ladders, sheets and frameworks. [source] 10-Benzyl-4-oxo-2,3,4,10-tetrahydropyrimido[4,5- b]quinolin-2-iminium chloride sesquihydrate: a polarized electronic structure within a complex hydrogen-bonded sheet structureACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Jorge Trilleras In the title compound, C18H15N4O+·Cl,·1.5H2O, one water site is fully ordered with unit occupancy while the other, which lies close to an inversion centre in the space group C2/c, has only 0.5 occupancy. The cation exhibits bond fixation in the fused carbocyclic ring and electronic polarization in the terminal heterocyclic ring. The components are linked into complex sheets by a combination of N,H...O, N,H...Cl, O,H...O, O,H...Cl and C,H...O hydrogen bonds. [source] (9E)-9-Benzylidene-3-methyl-2-methylsulfanyl-5-phenyl-5,6,7,8,9,10-hexahydropyrimido[4,5- b]quinolin-4(3H)-one: polarized molecules within hydrogen-bonded bilayersACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2010Diana Becerra The molecules of the title compound, C26H25N3OS, which was prepared by means of an acid-catalysed cyclocondensation reaction between a 6-aminopyrimidinone and 2,6-dibenzylidenecyclohexanone, exhibit a polarized electronic structure, namely (9E)-9-benzylidene-3-methyl-2-methylsulfanyl-5-phenyl-3,5,6,7,8,9-hexahydropyrimido[4,5- b]quinolin-10-ium-4-olate, involving charge separation in the vinylogous amide portion. Four hydrogen bonds, two each of the C,H...O and C,H...,(arene) types, link the molecules into bilayers comprising inversion-related pairs of sheets, each containing a single type of R43(36) ring. [source] 5-Amino-3-methyl-1-phenyl-1H -pyrazole-4-carbaldehyde hemihydrate: a polarized electronic structure within hydrogen-bonded sheets of R108(34) ringsACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2010Jairo Quiroga In the title compound, C11H11N3O·0.5H2O, the water molecule lies across a twofold rotation axis in the space group Pbcn. The bond distances in the organic component provide evidence for polarization of the electronic structure. The molecular components are linked into puckered sheets of R108(34) rings by a combination of O,H...N and N,H...O hydrogen bonds; adjacent sheets are weakly linked by an aromatic ,,, stacking interaction. Comparisons are made with some fused-ring analogues. [source] | ||||||||||