Electronic spectra and structures of protonated pyrazine and quinoxaline N-oxides

Dvoryantseva, G. G.; Kaganskii, M. M.; Musatova, I. S.; Elina, A. S.

doi:10.1007/bf01175101

Cited by 3 publications

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“…The first protonation of the mono-N-oxides of pyrazine and quinoxaline occurs at the unoxidized nitrogen atom [28,29], the unshared electron pair of which is not included in the conjugation chain (however the interaction of pyrazine mono-N-oxide with iodine proceeds at the oxygen atom of the N-oxide group [30]). …”

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The effect of electronic factors on the reactivity of heteroaromatic N-oxides

Andreev

2010

Chem Heterocycl Comp

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On the basis of an analysis of the reasons for the multiplicity of constants for substituents it has been concluded that they are variables, the absolute value and sign of which depend on the nature of the compounds being considered (in particular other substituents), the partner with which reaction occurs, and the medium (the aggregate state of participants of the interaction). The use of modifications of the Hammett equation is caused by the impossibility in principle of only varying the values and sign of to describe universally linear functions of the dependence of rate (or equilibrium) constants of chemical processes from the algebraic sum of the electronic, steric, and other factors, which differ in their nature.At the present time empirical equations of the Hammett and Taft type (log(k/k 0 ) = ) are widely used in organic chemistry in spite of the fact that the multiplicity of constants requires greater care in choosing them for making correlations, and the use for interpreting the structure of a transition state interferes with certain other resistant concepts [1-6]. Thus the Hammett equation is used for assessing the structure of a transition state (according to the size of ) among similar compounds by the variation of substituents and consequently by the change in reactivity. It is therefore assumed that is a constant (but is dependent on the nature of the second reactant and the reaction conditions), i.e. the nature ( ) of a substituent does not affect the structure of the transition state. However according to the Hammond postulate [5] in rapid reactions the transition state is more like the reactants, but in slow reactions it is more like the reaction products, i.e. on changing the reaction rate the structure of the transition state must also be changed.In the monograph [4] V. A. Palm notes that the problem of constructing a precise scale even for induction constants of substituents of the type of functional groups or containing functional groups has no solution. The assumption of even O. A. Reutov, A. L. Kurts, and K. P. Butin [5, Vol. 1, p. 288], that " and are not independent parameters, as suggested, but are linked to one another, while a parameter linking and is reduced in their product", does not only not clarify the situation, but also remains as an additional problem as to the nature of this parameter.

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The effect of electronic factors on the reactivity of heteroaromatic N-oxides

Andreev

2010

Chem Heterocycl Comp

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“…The point group There is some disagreement in the literature as to whether the nitrogen or the oxygen is protonated first in pyrazine-N-oxide. TWo reports suggest that the nitrogen atom is first to be protonated (67,68), while another suggests that the oxygen is first to be protonated, when a 2 so 4 is used as the acid (69). One of these investigations did find that pyrazine-di-N-oxide was only slowly protonated compared to the pyrazine-N-oxide, and it may be reasonable to assume therefore that the nitrogen atom is protonated first.…”

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High valent chromium (V) and chromium (VI) complexes

Davis¹

2000

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A new preparative route to the only neutral chromium CV> oxide fluoride, chromium oxide trifluoride, has been accomplished by the reaction of xenon difluoride with chromyl fluoride at high temperature. The chromium oxide trifluoride is produced as crystals which are suitable for single crystal studies. In reactions of chromium oxide trifluoride with alkali and alkaline metal fluorides in anhydrous hydrogen fluoride, new chromium(V) oxide fluoride salts were obtained; these salts were not of high purity due to unknown problems. An attempt to prepare chromium oxide tetrafluoride by the reaction of xenon difluoride with chromyl fluoride in anhydrous hydrogen fluoride failed to produce the desired product. 2The new chromiumCVI) complexes naphthyridinium chlorochromate CNapCC), pyrazinium chlorochromate CPzCC), pyrazinium-N-oxide chlorochromate CPzOCC), tripyridinium chlorochromate CTPCC), naphthyridinium dichromate CNapDC), pyrazinium trichromate CPzTC), and pyrazine chromiumCVI) oxide CPzCA) were prepared; the chlorochromates were readily produced as orange crystalline products in 6M HCl, the dichromate and trichromate complexes were produced in distilled water as crystalline products, and the chromium (VI) oxide complex was produced by the inert atmosphere reaction of pyrazine and chromium trioxide in dichloromethane.The chromiumCVI) complexes NapCC, PzCC, PzOCC, TPCC, and NapDC were all studied as oxidizing agents for the oxidation of alcohols. Except for PzOCC, all of these complexes are milder oxidants than pyridinium chlorochromate CPCC), and NapDC is highly selective for the oxidation of benzyl alcohol. Inf rared Spectrum of CC9H7N2>Cr03Cl . . HIGH VALENT CHROMIUM(V)AND X-Ray Powder Pattern of CC4H5N2>Cr03ClInf rared Spectrum of CC4H5N2>Cr03Cl . . X-Ray Powder Pattern of CC4H5N20>Cr03ClInf rared Spectrum of CC4H5N20)Cr03Cl . A number of oxotetrachloro and oxopentachloro pentavalent chromium salts have been prepared using this method, and a large number of publications on the spectroscopic properties have appeared in the literature during the last 25 years C3, Although PCC is a milder oxidant than sodium or potassium dichromate, and produces carbonyl compounds in good yields, it does not preferentially oxidize specific alcohols Ci.e.primary, secondary, benzylic, and allylic alcohols are not separately distinguished) and the need remains for selective oxidants.Since the report of the now well known PCC, several other chlorochromate and dichromate complexes having different heterocyclic cations have been reported. The pyridinium dichromate complex is easily prepared by the aqueous reaction of pyridine and chromium trioxide C33): 11The bipyridinium chlorochromate complex is formed in an analogous fashion to the pyridinium chlorochromate complex, while the bipyridine-chromium oxide complex is formed analogously to the dipyridine-chromiumCVI) oxide complex C34).Quite recently the 4-Cdimethylamino)pyridinium chlorochromate complex (35), as well as our own naphthyridinium and pyrazinium chlorochromate complexes (36...

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Quinoxaline Mono‐ and Di‐ N ‐Oxides

1979

Chemistry of Heterocyclic Compounds: A Series of Monographs

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Electronic spectra and structures of protonated pyrazine and quinoxaline N-oxides

Cited by 3 publications

References 5 publications

The effect of electronic factors on the reactivity of heteroaromatic N-oxides

The effect of electronic factors on the reactivity of heteroaromatic N-oxides

High valent chromium (V) and chromium (VI) complexes

Quinoxaline Mono‐ and Di‐ N ‐Oxides

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