Calculations of the Effects of Substituents on the Conformations of Pbzt and Pbo Model Compounds

1988 ◽  
Vol 134 ◽  
Author(s):  
B. L. Farmer ◽  
Scott G. Wierschke ◽  
W. W. Adams
Keyword(s):  
Phenyl Ring ◽  
Critical Parameter ◽  
Molecular Orbital Calculations ◽  
Methyl Ethyl ◽  
Model Compounds ◽  
X Ray ◽  
Torsional Potential ◽  
Conformational Properties ◽  
Conformational Freedom ◽  
Conformational Energies

ABSTRACTSemiempirical energy calculations have been used to investigate the conformational properties of poly(p-phenylene benzobisthiazole) (PBZT) and poly(p-phenylene benzobisoxazole) (PBO) having various substituents on the phenyl ring. Substituents considered included methyl, ethyl, t-butyl, hydroxyl, phenyl, and benzthiazole groups. The torsional potential for rotation about the backbone bond joining the phenylene and heterocyclic rings has a significant influence on the conformational energies. X-ray structure data and results of semiempirical molecular orbital calculations were used to determine this critical parameter.The results show that most substituents have surprisingly little influence on the conformations of the molecules. In most cases, the substituent causes a rotation of the backbone rings away from coplanarity, but once the steric interactions are relieved, there is considerable latitude for further rotation. The substituents most effective in locking the molecules into specific conformations were hydroxyl and t-butyl, due, respectively, to the prospect for hydrogen bonding, and non-planarity. In most cases, the conformational freedom is such that packing considerations could significantly influence the conformations of the materials in the solid state.

Configuration on the C=N double bond of monosubstituted amidines and amidoximes

1989 ◽  
Vol 54 (12) ◽  
pp. 3245-3252 ◽  
Author(s):  
Bernard Tinant ◽  
Janine Dupont-Fenfau ◽  
Jean-Paul Declercq ◽  
Jaroslav Podlaha ◽  
Otto Exner
Keyword(s):  
Double Bond ◽  
Nitrogen Atom ◽  
Steric Effects ◽  
Model Compounds ◽  
X Ray ◽  
Analogous Model

Configuration on the C=N double bond of amidines and amidoximes is controlled by steric effects on the second nitrogen atom but there is a difference in the case of N’-monosubstituted derivatives: amidines prefer E configuration (conformation around the C-N bond sp) and amidoximes Z configuration (conformation ap). This was confirmed by the X-ray structures of two analogous model compounds N,N’-dimethyl-4-nitrobenzamidine (monoclinic, P21c, a = 10.855(3), b = 11.043(3), c = 8.593(3) Å, β = 105.69(2)°, V = 991.8(5) Å3, Z = 4, Dx = 1.29 g cm-3, CuKα, λ = 1.5418 Å, μ = 7.91 cm-1, F(000) = 408, T = 291 K, R = 0.065 for 1 265 observed reflections) and N’-methyl-4-nitrobenzamidoxime (monoclinic, P21/a, a = 6.699(2), b = 24.178(9), c = 6.075(2) Å, β = 106.20(3)°, V = 944.9(6) Å3, Z = 4, Dx = 1.37 g cm-3, CuKα, λ = 1.5418 Å, μ =9.22 cm-1, F(000) = 408, T = 291 K, R = 0.079 for 1 278 observed reflections).

A pairwise additivity scheme for conformational energies of substituted ethanes

1975 ◽  
Vol 343 (1632) ◽  
pp. 1-10 ◽  
Keyword(s):  
Large Deviations ◽  
Ab Initio ◽  
Dihedral Angle ◽  
Molecular Orbital ◽  
Methyl Groups ◽  
Molecular Orbital Calculations ◽  
Linear Combinations ◽  
Strongly Interacting ◽  
Conformational Energies

Ab initio molecular orbital calculations are used to explore additivity in the conformational energies of poly-substituted ethanes in terms of conformational energies of ethane and appropriate mono- and 1,2-di-substituted derivatives. Such relations would allow complex calculations for poly-substituted ethanes to be replaced by much simpler ones on a small number of parent molecules. General expressions for the linear combinations are derived from the assumption that interactions between vicinal substituents are pairwise additive and depend only on the vicinal dihedral angle. The additivity scheme is tested for 15 ethanes, di-, tri- or tetrasubstituted by cyano and methyl groups and for a smaller number of fluoroethanes. Additivity applies to within 0.1- 0.3 k J mol -1 in the methylethanes and mostly to within about 0.7- 0.8 kJ mol -1 in cyanoethanes. Large deviations are found among the geminally substituted fluoroethanes. It is suggested that the additivity approximation is most successful in the absence of strongly interacting geminal groups. Predictions are made of conformational energies of ten hexa(cyano- and methyl-) substituted ethanes.

ChemInform Abstract: Syntheses and X-Ray Structures for Model Compounds of a Pyrimidinediyl- Based Rigid-Rod Aromatic Polyamide.

ChemInform ◽  
2010 ◽  
Vol 23 (17) ◽  
pp. no-no
Author(s):  
A. G. OERTLI ◽  
W. R. MEYER ◽  
U. W. SUTER ◽  
F. B. JOHO ◽  
V. GRAMLICH ◽  
...  
Keyword(s):  
Aromatic Polyamide ◽  
Model Compounds ◽  
X Ray ◽  
Rigid Rod

W-Doped TiO2 Preparation and Photocatalytic Degradation of Guaiacol

2014 ◽  
Vol 513-517 ◽  
pp. 33-36 ◽  
Author(s):  
Zi Chang Xie ◽  
Ying Wang ◽  
Peng Wang ◽  
Lei Zhang
Keyword(s):  
Photocatalytic Activity ◽  
Visible Light ◽  
Photocatalytic Degradation ◽  
Degradation Rate ◽  
Amorphous State ◽  
X Ray Diffraction ◽  
Model Compounds ◽  
Plant Fibers ◽  
X Ray ◽  
Crystallite Structure

In this paper, W-doped TiO2 (W-TiO2) powder was prepared in hydrothermal method by mixing TiO2 and ammonium metatungstate. The catalysts were characterized by X-ray diffraction and ultraviolet spectrophotometer. The results displayed that W-TiO2 showed an anatase crystallite structure with 2 % W content. W-element in W-TiO2 was amorphous state. The guaiacol was degraded with the W-TiO2 in the visible light. It was a model compounds of lignin existed in the plant fibers. The degradation rate of guaiacol was increased with the photocatalytic time, as high as 88.21 % after 360 min irradiation. It was concluded that the W-TiO2 had an obvious photocatalytic activity under visible light. It can be used in the photocatalytic degradation of lignin.

Near edge X-ray absorption fine structure (NEXAFS) of model compounds for the humic acid/actinide ion interaction

2005 ◽  
Vol 148 (3) ◽  
pp. 151-157 ◽  
Author(s):  
Markus Plaschke ◽  
Jörg Rothe ◽  
Marcus Altmaier ◽  
Melissa A. Denecke ◽  
Thomas Fanghänel
Keyword(s):  
Fine Structure ◽  
Humic Acid ◽  
Model Compounds ◽  
X Ray ◽  
Absorption Fine ◽  
X Ray Absorption

Structure of macrophage migration inhibitory factor in complex with methotrexate

2021 ◽  
Vol 77 (3) ◽  
pp. 293-299
Author(s):  
Kei Fukushima ◽  
Minoru Furuya ◽  
Takashi Kamimura ◽  
Midori Takimoto-Kamimura
Keyword(s):  
Rheumatoid Arthritis ◽  
Dihydrofolate Reductase ◽  
Migration Inhibitory Factor ◽  
Macrophage Migration Inhibitory Factor ◽  
Inhibitory Factor ◽  
Molecular Orbital Calculations ◽  
Macrophage Migration ◽  
Affinity Matrix ◽  
Nucleotide Synthesis ◽  
X Ray

Methotrexate (MTX) is an anticancer and anti-rheumatoid arthritis drug that is considered to block nucleotide synthesis and the cell cycle mainly by inhibiting the activity of dihydrofolate reductase (DHFR). Using affinity-matrix technology and X-ray analysis, the present study shows that MTX also interacts with macrophage migration inhibitory factor (MIF). Fragment molecular-orbital calculations quantified the interaction between MTX and MIF based on the structure of the complex and revealed the amino acids that are effective in the interaction of MTX and MIF. It should be possible to design new small-molecule compounds that have strong inhibitory activity towards both MIF and DHFR by structure-based drug discovery.

SUPERSTRIPES BY ANOMALOUS X-RAY DIFFRACTION AND ANGLE RESOLVED PHOTOEMISSION IN BI2212

2000 ◽  
Vol 14 (29n31) ◽  
pp. 3649-3655 ◽  
Author(s):  
N. L. SAINI ◽  
A. BIANCONI
Keyword(s):  
Fermi Surface ◽  
Energy Distribution ◽  
Critical Parameter ◽  
Nearest Neighbor ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lattice Coupling

We show an evidence for the superconducting stripes (superstripes) in the Bi2212 system by joint x-ray diffraction and angle resolved photoemission. The kink observed at k y =0.4π in the energy distribution curves is shown to be related to a modulation of the Cu displacement out of the oxygen plane with a wavevector Q ~(0.4π, 0.4π) that modulates the next-nearest neighbor hopping integral t ′. The resulting Fermi surface reveals broken segments around the M points due to the modulation of the t ′, associated with modulation of the electron-lattice coupling λ(ε) that depends on the micro strain ε of the CuO 2 plane. The present findings further enlightens the fact that the micro-strain, controlling the electron-lattice coupling λ(ε) is a critical parameter for the superstripes.

Molecular motions of a tetraphenylethylene-derived AIEgen directly monitored through in situ variable temperature single crystal X-ray diffraction

CrystEngComm ◽  
2021 ◽  
Author(s):  
Wei Meng ◽  
Lin Du ◽  
Lin Sun ◽  
Lian Zhou ◽  
Xiaopeng Xuan ◽  
...  
Keyword(s):  
Single Crystal ◽  
Phenyl Ring ◽  
Functional Group ◽  
Variable Temperature ◽  
Molecular Motions ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray ◽  
Conformation Changes

One organic functional group was introduced to distinguish the four phenyl ring of tetraphenylethylene, and the In situ temperature-dependent crystal structures were determined to exhibit the conformation changes of tert-butyl...

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