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.

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 HR-DOSY and sulfoxide enantiomeric discrimination by cyclodextrin

2000 ◽  
Vol 14 (4) ◽  
pp. 203-213 ◽  
Author(s):  
Ricardo Batista Borges ◽  
Antonio Laverde Jr. ◽  
André Luiz Meleiro Porto ◽  
Anita Jocelyne Marsaioli
Keyword(s):  
Chiral Recognition ◽  
Chemical Shifts ◽  
Binding Constants ◽  
Chiral Selector ◽  
Point Of View ◽  
The Other ◽  
Stoichiometric Ratio ◽  
Enantiomeric Resolution ◽  
Rp Hplc ◽  
C Nmr

Racemic and chiral ethyl-phenylsulfoxide (solute) andβ-cyclodextrin (chiral selector) were used to compare two NMR methodologies to predict RP-HPLC enantiomeric resolution efficiency. One of them based on the classical approach involving apparent binding constants and complexation‒induced chemical shifts at saturation and the other based on13C NMR signal splittings (solute and chiral selector in stoichiometric ratio) and HR-DOSY of the same solution. We have concluded that the latter methodology is rather efficient and though more elaborate from the NMR point of view, the results are promising and constitute an alternative method to investigate chiral recognition and other supramolecular phenomena.

13C N.M.R. STUDIES: VIII. 13C SPECTRA OF SOME SUBSTITUTED ANISOLES

1966 ◽  
Vol 44 (23) ◽  
pp. 2855-2866 ◽  
Author(s):  
K. S. Dhami ◽  
J. B. Stothers
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Aromatic Ring ◽  
Steric Hindrance ◽  
Steric Effect ◽  
Chemical Shifts ◽  
Methoxyl Group ◽  
Side Chains ◽  
Nuclear Magnetic Resonance Spectra ◽  
Magnetic Resonance Spectra

The 13C nuclear magnetic resonance spectra of a series of 40 substituted anisoles have been obtained to investigate the effects of substitution on the aromatic and methoxyl carbon shieldings. This work extends our studies on the variations of chemical shifts of carbon nuclei in side chains of aryl derivatives. The question of steric hindrance to conjugative interaction of a methoxyl group with an aromatic ring is considered on the basis of the present results. Evidence of a steric effect in compounds in which both ortho positions are substituted is presented.

Embryonic Responses to Structurally Related Inhibitors

Development ◽  
1960 ◽  
Vol 8 (4) ◽  
pp. 445-456
Author(s):  
Kathe Liedke ◽  
H. B. Gillespie ◽  
Samuel Graff
Keyword(s):  
Nitro Group ◽  
Rana Pipiens ◽  
The Other ◽  
Amino Group ◽  
Inhibitory Effects ◽  
Tail Bud ◽  
Cytotoxic Effects ◽  
Other Hand

Substituted benzotriazoles (Bt) have been shown to bring about interesting inhibitory effects on Rana pipiens embryos of 2-cell to tail-bud stages (Liedke, Engelman, & Graff, 1954, 1955, 1957a, 1957b). These benzotriazoles did not have selective cytotoxic effects on sensitive embryonic structures as similarly substituted benzimidazoles (Bz) and quinoxalines (Q) invariably did. The latter compounds, Bz and Q, were most active against younger stages, especially those in cleavage. On the other hand, it was found that the susceptibility to the benzotriazoles increased with age of embryo; more differentiated stages were affected most. The type of response was determined by the parent structure, but certain substituents, the nitro group in particular, appeared to enhance the magnitude of the effect. The activating effect of the nitro group was in turn modified to varying degree by an accompanying methoxy, hydroxy, or amino group.

RING-PROTON CHEMICAL SHIFTS OF SOME SUBSTITUTED ANILINES IN CARBON TETRACHLORIDE AND TRIFLUOROACETIC ACID

1963 ◽  
Vol 41 (9) ◽  
pp. 2339-2345 ◽  
Author(s):  
W. F. Reynolds ◽  
T. Schaefer
Keyword(s):  
Carbon Tetrachloride ◽  
Steric Hindrance ◽  
Trifluoroacetic Acid ◽  
Electronic Spectra ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Amino Group ◽  
Substituted Anilines ◽  
Ring Proton ◽  
Proton Chemical Shifts

The chemical shifts of the ring-proton spectra of a series of substituted anilines are reported relative to internal benzene in the solvents carbon tetrachloride and trifluoroacetic acid. The substituent parameters in cyclohexane derived by Martin can be used together with our parameters for the para-fluoro and -ammonio (NH3+) groups to demonstrate additivity of the substituent effects in both carbon tetrachloride and trifluoroacetic acid. The somewhat puzzling ring-proton shifts in the latter solvent are attributed to counterion effects arising from a juxtaposition of the two centers of charge. Steric hindrance to π-overlap of the amino group with the ring is demonstrated in certain cases and a parallel behavior is found between the ring-proton shifts and the electronic spectra of these molecules.

Regioselective Nitration of Halogenated Benzo[c]cinnolines and Benzenoids

2015 ◽  
Vol 3 (8) ◽  
pp. 136-153
Author(s):  
Ayunna K Epps ◽  
Tonya M Horne ◽  
Sha Nese Jackson ◽  
Bridgette Sands ◽  
Ghislain R Mandouma
Keyword(s):  
Nitro Group ◽  
Aromatic Ring ◽  
Steric Hindrance ◽  
Mixed Acid ◽  
Ring Group ◽  
Temperature Conditions ◽  
Mild Temperature ◽  
Regioselective Nitration

Electrophilic nitration of halo-substituted benzo[c]cinnolines and benzenoids has been achieved regioselectively. The nitro group entry was always ortho to the halo group or/and the aromatic ring. This regioselective electrophilic ortho-nitration was accomplished in mixed acid/mild temperature conditions. Regioselectivity ortho to the halo/ring group(s) was observed with or without proximal steric hindrance. Chlorides and bromides worked equally well in directing these high-yielding ortho-selective reactions.

Determination of coupling constants of nitrogen in amino group of nitroanilines by means of relaxation times in rotating frame

1983 ◽  
Vol 48 (4) ◽  
pp. 984-988 ◽  
Author(s):  
Vladimír Mlynárik
Keyword(s):  
Nitro Group ◽  
Relaxation Times ◽  
Amino Nitrogen ◽  
Coupling Constants ◽  
Aromatic Nucleus ◽  
Amino Group ◽  
Rotating Frame

One-bond coupling constants of amino nitrogen in 2-, 3- and 4-nitroanilines have been calculated on the basis of 1H and 13C relaxation times in rotating frame (T1ρ) which are affected by interaction with rapidly relaxing 14N nucleus. A method has been suggested and tested for calculation of 14N-13C couplings with elimination of effects of other relaxation mechanisms. Dependence of 1J(14N13C) on position of nitro group in the aromatic nucleus has been observed.

Substituent-Dependent Nitration of 9-Substituted 9,10-Dihydro-9,10-ethanoanthracenes

1995 ◽  
Vol 48 (12) ◽  
pp. 1949 ◽  
Author(s):  
MC Harsanyi ◽  
RK Norris ◽  
G Sze ◽  
PK Witting
Keyword(s):  
Nitro Group ◽  
Aromatic Ring ◽  
The Other ◽  
Aromatic Rings

Mononitration of 9-substituted ethanoanthracenes, bearing Me, But, F, Br, I, OMe , NO2, CN, CHO or CO2Me substituents at the bridgehead carbon, was found to occur exclusively at the β-positions of the aromatic ring. The mononitro products were isolated, identified by 1H n.m.r. spectroscopy, and their relative proportions were estimated by quantitative g.l.c . and/or by 1H n.m.r. spectroscopy. For all the above substrates the proportion of nitration at the β-position meta to the bridgehead carbon bearing the substituent [to give compounds of the general form (4)] was greater than the proportion of nitration at the corresponding β-position para to the bridgehead substituent [to give compounds of the general form (3)]. Whilst the preferential nitration at the β-positions of the aromatic rings is consistent with the previously reported nitration of 9,10-dihydro-9,10-ethanoanthracene (2a) itself, no observations of this preferential meta attack have been made previously. No correlation could be made of this behaviour with available substituent parameters for the widely sterically and electronically disparate set of substituents used in this study, and the origin of this preferential attack remains unclear. Dinitration in this system was studied only superficially. The influence of the bridgehead substituent together with that of the nitro group already present on one aromatic ring appear to combine with quite unpredictable results in orienting the position of attack of the incoming nitro group onto the other (non-nitrated) aromatic ring.

Can the Academic Self-Concept be Positive and Realistic?

2005 ◽  
Vol 19 (3) ◽  
pp. 129-132 ◽  
Author(s):  
Reimer Kornmann
Keyword(s):  
Academic Performance ◽  
Opposite Effect ◽  
Self Esteem ◽  
Point Of View ◽  
The Other ◽  
Self Concept ◽  
High Ability ◽  
Self Image ◽  
Other Hand

Summary: My comment is basically restricted to the situation in which less-able students find themselves and refers only to literature in German. From this point of view I am basically able to confirm Marsh's results. It must, however, be said that with less-able pupils the opposite effect can be found: Levels of self-esteem in these pupils are raised, at least temporarily, by separate instruction, academic performance however drops; combined instruction, on the other hand, leads to improved academic performance, while levels of self-esteem drop. Apparently, the positive self-image of less-able pupils who receive separate instruction does not bring about the potential enhancement of academic performance one might expect from high-ability pupils receiving separate instruction. To resolve the dilemma, it is proposed that individual progress in learning be accentuated, and that comparisons with others be dispensed with. This fosters a self-image that can in equal measure be realistic and optimistic.

RHYNCHOLITES AND THE PROBLEM OF NARROW AND BROAD CONCEPTION OF TAXONS

2018 ◽  
pp. 12-17 ◽  
Author(s):  
I. R. Khuzina ◽  
V. N. Komarov
Keyword(s):  
Sexual Dimorphism ◽  
Morphological Characteristics ◽  
Mass Scale ◽  
Individual Variability ◽  
Point Of View ◽  
The Other ◽  
New Taxon ◽  
Artificial System ◽  
Broad Understanding

The paper considers a point of view, based on the conception of the broad understanding of taxons. According to this point of view, rhyncholites of the subgenus Dentatobeccus and Microbeccus are accepted to be synonymous with the genus Rhynchoteuthis, and subgenus Romanovichella is considered to be synonymous with the genus Palaeoteuthis. The criteria, exercising influence on the different approaches to the classification of rhyncholites, have been analyzed (such as age and individual variability, sexual dimorphism, pathological and teratological features, degree of disintegration of material), underestimation of which can lead to inaccuracy. Divestment of the subgenuses Dentatobeccus, Microbeccus and Romanovichella, possessing very bright morphological characteristics, to have an independent status and denomination to their synonyms, has been noted to be unjustified. An artificial system (any suggested variant) with all its minuses is a single probable system for rhyncholites. The main criteria, minimizing its negative sides and proving the separation of the new taxon, is an available mass-scale material. The narrow understanding of the genus, used in sensible limits, has been underlined to simplify the problem of the passing the view about the genus to the other investigators and recognition of rhyncholites for the practical tasks.

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