Regioselectivity of nucleophilic aromatic photosubstitution in the biphenyl series. Photohydrolysis of some dimethoxynitrobiphenyls

1987 ◽  
Vol 52 (10) ◽  
pp. 2482-2491 ◽  
Author(s):  
Ján Urban ◽  
Petr Kuzmič ◽  
David Šaman ◽  
Milan Souček
Keyword(s):  
Nitro Group ◽  
Steric Hindrance ◽  
The Other ◽  
Quantum Yields ◽  
Hydroxide Anion ◽  
Tert Butanol ◽  
Nitro Derivatives

Anaerobic photolysis of dimethoxynitrobiphenyls IIIa-VIa in aqueous alkaline tert-butanol gave products of nucleophilic photosubstitution of methoxyl by hydroxide anion, while the dimethoxybiphenyls Ia and IIa were found unreactive. Regioselectivity of the reaction was examined in view of a possible “extended meta activation” by the nitro group. The most reactive substrate IIIa gives both C-3 and C-4 substitution products with an unsubstantial preference for the latter, which opposes the “extended meta selectivity” rule. All of the other compounds obey the rule, and 3,4-dimethoxy-3'-nitrobiphenyl (IVa) even displayed absolute selectivity by yielding C-3 substituted compound as the only product. 2,5-Dimethoxy substituted compounds underwent photosubstitution which much lower quantum yields than their 3,4-substituted counterparts, most probably due to some steric hindrance of conjugation. Similarly, 3-nitro-substituted biphenyls exhibited much lower overall reactivity than 4-nitro derivatives.

scholarly journals Nitrogen NMR shieldings of 2-amino-5-nitro-6-methylpyridines

1997 ◽  
Vol 13 (4) ◽  
pp. 251-256 ◽  
Author(s):  
B. Palasek ◽  
A. Puszko ◽  
Z. Biedrzycka ◽  
W. Sicinska ◽  
M. Witanowski
Keyword(s):  
Nitro Group ◽  
Aromatic Ring ◽  
Steric Hindrance ◽  
Chemical Shifts ◽  
Amino Nitrogen ◽  
Point Of View ◽  
The Other ◽  
Amino Group ◽  
Alkyl Aryl ◽  
Pyridine Nitrogen

Nitrogen NMR shieldings (chemical shifts) of 2-amino-5-nitro-6-methylpyridine derivatives are assessed from the point of view of substituent-induced effects under conditions where alkyl, aryl, nitro, and nitroso moieties are substituents at the amino nitrogen. The nitro nitrogen shielding reveals only little variation upon varying the substituents, and this seems to indicate that steric hindrance which is likely to force the nitro group out of the plane of the aromatic ring reduces theπ-electron conjugation with the latter, and with the amino group as well. On the other side, the pyridine nitrogen shielding shows large effects of substituents at the amino moiety, which suggests a significant conjugation between the ring and the amino group. The latter effects produce a remarkable deshielding of the pyridine nitrogen in the case of nitro and nitroso substituents at the amino group.

scholarly journals N-(4-Ethoxy-2,5-dinitrophenyl)acetamide

IUCrData ◽  
2020 ◽  
Vol 5 (8) ◽  
Author(s):  
Sannihith N. Uppu ◽  
Ogad A. Agu ◽  
Curtistine J. Deere ◽  
Frank R. Fronczek
Keyword(s):  
Hydrogen Bond ◽  
Nitro Group ◽  
Benzene Ring ◽  
Title Compound ◽  
The Other ◽  
Ring Plane ◽  
Torsion Angles ◽  
Compound C ◽  
Bifurcated Hydrogen Bond

In the title compound, C10H11N3O6, the torsion angles about the bonds to the benzene ring are less than 4°, except for the nitro groups, which are twisted out of the ring plane by 25.27 (3) and 43.63 (2)°. The N—H group forms a bifurcated hydrogen bond, with an intramolecular component to a nitro group O atom and an intermolecular component to the other nitro group, thereby forming chains propagating in the [010] direction. Several weak C—H...O interactions are also present.

The Boger Synthesis of (+)-Complestatin

2013 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Nitro Group ◽  
The Other ◽  
Aryl Ether ◽  
Silyl Group ◽  
Model Studies ◽  
La Jolla ◽  
Indole Synthesis ◽  
Modular Nature

(+)-Complestatin 3 shows promising activity against HIV infectivity. Dale L. Boger of Scripps/La Jolla described (J. Am. Chem. Soc. 2010, 132, 7776) an elegant multicomponent assembly of 3, the key step of which was the atropisomer-selective intramolecular Larock cyclization of 1 to 2. The preparation of 1 began with the protected phenethylamine 5, prepared by Sharpless asymmetric aminohydroxylation of the styrene 4. Conversion of 5 to the areneboronic acid followed by coupling with 6 delivered 7. Acylation led to 8, with the stage set for nitro-assisted addition-elimination, to form the first bis-aryl ether of 3. The product was a mixture of atropisomers, subsequently symmetrized to 9 by removal of the nitro group. Acylation of 9 led to 1. The role of the silyl group on the alkyne of 1 was to direct the regioselectivity of the intramolecular Larock indole synthesis. Again, two atropisomers were possible from the cyclization. Earlier model studies had suggested some preference for one over the other. As it turned out, in this case the desired atropisomer was the only one observed. It is particularly striking that the coupling was efficient even in the presence of the readily reduced and unprotected chlorophenols. The modular nature of this route to (+)-complestatin 3 will make it possible to prepare a variety of analogues. As long as only the substituents on the periphery are changed, the atropisomer selectivity in the Larock cyclization should be maintained.

Polypyridines, Picrates, Lanthanides: A Plethora of Stacks?

2020 ◽  
Vol 73 (6) ◽  
pp. 529
Author(s):  
Eric J. Chan ◽  
Simon A. Cotton ◽  
Jack M. Harrowfield ◽  
Brian W. Skelton ◽  
Alexandre N. Sobolev ◽  
...  
Keyword(s):  
Nitro Group ◽  
The Other ◽  
Molar Ratio ◽  
Lanthanide Ion ◽  
X Ray ◽  
The Third ◽  
Group Oxygen ◽  
Structure Determinations ◽  
Lighter Lanthanides ◽  
Trigonal Prismatic

Reactions of the lanthanide(iii) picrates (picrate=2,4,6-trinitrophenoxide=pic) with 1,10-phenanthroline (phen) and 2,2′:6′,2′′-terpyridine (terpy) in a 1:2 molar ratio have provided crystals suitable for X-ray structure determinations in instances predominantly involving the lighter lanthanides. In all, the aza-aromatic ligands chelate the lanthanide ion, none being found as ‘free’ ligands within the lattice. The complexes of 1,10-phenanthroline have been characterised in two forms, one unsolvated (Ln=La, Sm, Eu; monoclinic, C2/c, Z 8), one an acetonitrile monosolvate (Ln=Gd; monoclinic, P21/a, Z 4), the latter being the only previously known form (with Ln=La). In both forms, the LnIII is nine-coordinate, in an approximately tricapped trigonal-prismatic environment, with two picrate ligands chelating through phenoxide and 2-nitro group oxygen atoms, the third being bound through phenoxide-O only. The 2,2′:6′,2′′-terpyridine complexes, all acetonitrile monosolvates defined for Ln=La, Gd, Er, and Y (monoclinic, C2/c, Z 4), are ionic, one picrate having been displaced from the primary coordination sphere. For Ln=La, the two bound picrates are again chelating, making the LaIII 10-coordinate in a distorted bicapped square-antiprismatic environment but in the other species they are bound through phenoxide-O only, making the LnIII ions eight-coordinate in a distorted square-antiprismatic environment. Stacked arrays of the ligands can be found in both series of complexes, with intramolecular picrate–picrate and picrate–aza-aromatic stacks being prominent features.

scholarly journals Phosphoreszenzeigensch aften von Methyl-, Chlor- und Brom-Derivaten des [2.2] Paracyclophans

1987 ◽  
Vol 42 (9) ◽  
pp. 1041-1042 ◽  
Author(s):  
H. Hopf ◽  
E. Hermann
Keyword(s):  
Triplet State ◽  
Fluorescence Spectra ◽  
Heavy Atom ◽  
The Other ◽  
Quantum Yields ◽  
Heavy Atom Effect ◽  
Chloro Derivatives ◽  
Derivatives Of ◽  
Atom Effect

Phosphorescence and fluorescence spectra, quantum yields of phosphorescence and fluorescence as well as phosphorescence lifetimes have been measured of six methyl-, chloro- and bromo-derivatives of [2.2] paracyclophane in ethanol at 77 K. While the chloro-derivatives as well as dibromo-paracyclophane exhibit a normal internal heavy-atom effect behaviour the momobromo-compound shows anomalies. These possibly indicate that in the monobromo-compound an additional pathway of the radiationless deactivation of the lowest triplet state is effective which does not occur with the other compounds.

The spectral properties and photosensitivities of analogue photopigments regenerated with 10- and 14-substituted retinal analogues

1988 ◽  
Vol 233 (1270) ◽  
pp. 55-76 ◽  
Keyword(s):  
Schiff Base ◽  
Binding Site ◽  
Steric Hindrance ◽  
Visual Pigment ◽  
Spectral Properties ◽  
The Other ◽  
Porichthys Notatus ◽  
Counter Ion ◽  
Two Systems ◽  
Retinal Analogues

Analogues of 11- cis - and 9- cis -retinal with substitutions at positions 10 and 14 were used to regenerate analogue photopigments with two opsins: that of the transmuted (cone-like) 521-pigment of Gekko gekko and that of the rhodopsin of Porichthys notatus . The spectral absorbances and photosensitivities of the regenerated photopigments were determined and compared, first, between the two systems of analogue photopigments, and second, in the responses to the two opsins. Unlike the 10-fluoropigments, the comparable 14-compounds were significantly redshifted by 19–30 nm and their sensitivity to light was similar to that of the parent 11- cis - and 9- cis -pigments. These were the results for both analogue pigments. In contrast, the 10-pigments were spectrally located close to the wavelengths of the parent compounds and the photosensitivity was significantly reduced, especially in the case of the 9- cis -analogues. Evidence was obtained for a steric hindrance effect at position 14, for no regeneration was obtained when methyl or ethyl groups were at this carbon. In the 10-substituted retinals, steric hindrance was noted only for the gecko; only the fluorosubstituted, but not the chloro-, the methyl- or the ethyl-substituted, retinals reacted. With the fish opsin, pigments were regenerated with all but the ethyl-substituted retinal. The gecko opsin appears to have a more restricted binding site. Another feature of the gecko was related to the chloride bathochromic and hyperchromic effects, in which the 521-pigment prepared in a chloride-deficient state has a blue-shifted spectrum compared with the spectrum obtained after the addition of chloride, and its extinction is raised by the addition of chloride to give a mean ratio of 1.23 for the two extinctions, one with, the other without, added chloride. The 11- cis -10-F-analogue pigment gave both chloride effects and the hyperchromic ratio was the same as that recorded for the native visual pigment. In contrast, the pigment formed with 11- cis -14-F-retinal gave a hyperchromic ratio significantly greater than 1.23. A similar contrast in the responses to chloride was obtained with the analogue photopigments regenerated with the 9- cis -10-F- and 9- cis -14-F-chromophores. This difference between the two systems is interpreted as the result of a specific configurational feature of the gecko opsin when in the chloride-deficient state that is relevant to the binding of the retinal analogue. Together, the results point to a different interaction with the visual protein on the part of the 10- and 14-substituted retinals. The latter adjust the pigment colour by acting specifically at the opsin site of the negative counter ion responsible for adjusting the degree of protonation of the Schiff base nitrogen.

The possibilities of polarography in the chemistry of nitroazoles

1984 ◽  
Vol 49 (6) ◽  
pp. 1342-1353 ◽  
Author(s):  
Dragica Dumanović ◽  
Janka Ćirić ◽  
Djuro Kosanović ◽  
Dragoslav Jeremić
Keyword(s):  
Nitro Group ◽  
Systematic Investigation ◽  
Nitro Compounds ◽  
The Other ◽  
Polarographic Method ◽  
Spectrophotometric Methods ◽  
Group Position ◽  
High Yields

Based on systematic investigation of mononitroimidazoles, selective polarographic and spectrophotometric methods for determination of nitrazole compounds in reaction mixture are proposed. It was proved that the selectivity is based on the different properties of the nitro group due to the effects of the nitro group position in the ring, the type and position of the other substituents and on the fact whether the compound is N-substituted or not. The proposed methods can be successfully used for monitoring the synthetic procedures and decreasing the number of experiments for optimization. Based on the anticipated and proved behaviour of the nitro compounds of pyrazole, novel mononitropyrazole derivatives were synthetized in a new way and with high yields. Applying the polarographic method it was discovered that during N-substitution of tautomeric mononitroimidazole and mononitropyrazole substrates other byproducts were obtained besides the main products and undesired isomers. The products were identified and then a correct and more complete N-substitution scheme could be given. Following quantitatively these N-substitution processes conclusions which directly concern the mechanism of reactions were drawn.

A three-dimensional cadmium(II) coordination polymer with unequal homochiral double-stranded concentric helical chains

2015 ◽  
Vol 71 (4) ◽  
pp. 289-293 ◽  
Author(s):  
Wei Shi ◽  
Jian-Jun Liu ◽  
Xiang-Ping Ou ◽  
Chang-Cang Huang
Keyword(s):  
Coordination Polymer ◽  
Hydrogen Bonds ◽  
Three Dimensional ◽  
Cadmium Acetate ◽  
The Other ◽  
Acetate Anion ◽  
Asymmetric Unit ◽  
Hydrothermal Conditions ◽  
Helical Channel ◽  
Hydroxide Anion

A homochiral helical three-dimensional coordination polymer, poly[[(μ2-acetato-κ3O,O′:O)(hydroxido-κO)(μ4-5-nicotinamido-1H-1,2,3,4-tetrazol-1-ido-κ5N1,O:N2:N4:N5)(μ3-5-nicotinamido-1H-1,2,3,4-tetrazol-1-ido-κ4N1,O:N2:N4:N5)dicadmium(II)] 0.75-hydrate], {[Cd2(C7H5N6O)2(CH3COO)(OH)]·0.75H2O}n, was synthesized by the reaction of cadmium acetate,N-(1H-tetrazol-5-yl)isonicotinamide (H-NTIA), ethanol and H2O under hydrothermal conditions. The asymmetric unit contains two crystallographically independent CdIIcations, two deprotonated 5-nicotinamido-1H-1,2,3,4-tetrazol-1-ide (NTIA−) ligands, one acetate anion, one hydroxide anion and three independent partially occupied water sites. The two CdIIcations, with six-coordinated octahedral and seven-coordinated pentagonal bipyramidal geometries are located on general sites. The tetrazole group of one symmetry-independent NTIA−ligand links one of the independent CdIIcations into 61helical chains, while the other NTIA−ligand links the other independent CdIIcations into similar but unequal 61helical chains. These chains, with a pitch of 24.937 (5) Å, intertwine into a double-stranded helix. Each of the double-stranded 61helices is further connected to six adjacent helical chains through an acetate μ2-O atom and the tetrazole group of the NTIA−ligand into a three-dimensional framework. The helical channel is occupied by the isonicotinamide groups of NTIA−ligands and two helices are connected to each other through the pyridine N and carbonyl O atoms of isonicotinamide groups. In addition, N—H...O and O—H...N hydrogen bonds exist in the complex.

Molekülinterne Dipolorientierung und dielektrische Absorption in verdünnter Lösung bei Mikro-und Submillimeterwellen. V.Acetyl-Verbindungen

1989 ◽  
Vol 44 (9) ◽  
pp. 853-865
Author(s):  
Gerhard Klages
Keyword(s):  
Fourier Transform ◽  
Dielectric Loss ◽  
Steric Hindrance ◽  
Loss Factor ◽  
The Other ◽  
Fourier Transform Spectrometer ◽  
Aromatic Rings ◽  
Molecular Laser ◽  
Aliphatic Compounds ◽  
Fast Relaxation

Abstract The dielectric loss of sixteen molecules, eleven with the acetyle group in aromatic bonds and five in aliphatic bonds, has been measured in very dilute solutions of cyclohexene at 20 °C. Five of these molecules are investigated in decalene solutions, too. The measurements have been made at wavenumbers in the range 0.08 to 140 cm -1 above 8 cm -1 making use of a pumped molecular laser. They are supplemented by the data of a Fourier transform spectrometer up to 300 cm -1. All microwave spectra of loss factor ε″ are analysed in terms of three absorption areas using the two variable Mori formalism. On the other hand, Lorentz curves are fitted to the FIR absorption spectra of α(v̄).The fast relaxation process of the aliphatic compounds is suggested to be due to intramolecular reorientation of the acetyle group itself, since in acetyle cyclohexene the remaining part of the molecule is rigid. To the contrary, the acetyle group is not able to reorientate swiftly, if bounded to aromatic rings. Presumably, it is fixed by mesomeric interaction with the dipole in the plain of the ring. However, 2-methyl acetophenone and 1-acetyle naphthone show some quick dipole reorientation, which coincides with a steric hindrance of the group in entering the plain of the ring.

Chloroazobenzenes: Studies on Syntheses

1969 ◽  
Vol 24 (8) ◽  
pp. 994-996 ◽  
Author(s):  
H. A. B. Linke ◽  
R. Bartha ◽  
D. Pramer
Keyword(s):  
Chlorine Atom ◽  
Steric Hindrance ◽  
Bond Formation ◽  
The Other

Thirteen chloroazobenzenes were synthesized by reduction of chloronitrobenzenes or by oxidation of their corresponding chloroanilines. Five of the compounds have not been previously prepared or described. Reduction by LiAlH4 was the method of choice, but it proved inadequate for the syntheses of chloroazobenzenes from o-chloronitrobenzenes. This reaction eliminated chlorine if ortho to the aniline nitrogen and an additional chlorine atom; in the other cases steric hindrance of azo bond formation resulted in low yields. Chromatographic systems for the separation of pure chloroazobenzenes from the crude reaction mixtures were developed and are described.

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