Hydrazones structure

Acyl-, 4-alkoxycarbonyl- and 4-phenylazo-pyrazolin-5-ones present the possibility of a fourth tautomer with an exocyclic double bond and a chelated structure. The molecular structure of (138) has been determined by X-ray crystallography (Table 5). It was shown that the hydroxy group participates in an intramolecular hydrogen bond with the carbonyl oxygen atom of the ethoxycarbonyl group at position 4 (8OCSCII21). On the other hand, the fourth isomer is the most stable in 4-phenylazopyrazolones (139), a chelated phenyl-hydrazone structure. 

Diazo-coupling products of 1-substituted l//-pyrrol-3(2//)-ones have been shown by X-ray crystallography to adopt the hydrazone structure 115 [91JCS(P1)701]. 

Preliminary studies with a thio derivative of isatin (indole-2-thione-3-phenylhydrazone) also showed the hydrazone structure to be the favored tautomeric form (81JOC2764). 

The hydrazone structure 40 can be eliminated at once many examples of this class of compounds are known and their properties are completely different from the diaziridines. For example, 3,3-dimethyldiaziridine has a heat of combustion of about 35 kcal higher than the isomeric acetone hydrazone. Further pairs of isomers of diaziridines and hydrazones are known. The spectrum eliminates both the hydrazone structure and the betaine structure 41. The diaziridines do not absorb in the UV range. In the infrared spectrum, absorption is completely absent in the double-bond region. - The NMR spectrum of 3,3-dimethyldiaziridine is in agreement with a formulation that has two equivalent iV-protons. ... 

The aromatic nature of the SFB and SANH reactants create a hydrazone structure with unique absorptivity for monitoring the course of the ligation process. The aromatic hydra-zone bond has a maximal absorbance at 354nm and a molar extinction coefficient equal to... 

The phenylazonaphthols present a particularly interesting series. Despite the partial loss of aromaticity in the hydrazone structures that can be drawn for l-phenylazo-2-naphthol, 2-phenylazo-l-naphthol and 4-phenylazo-l-naphthol, these structures are not much higher in energy than the azo forms [50], so that there should be no significant preference for one form over the other. When the visible absorption curves of 4-phenylazo-l-naphthol are measured in a variety of solvents, they all pass through a common point (isosbestic point) as in Figure 4.1 [51,52]. l-Phenylazo-2-naphthol shows similar behaviour. This finding is clear evidence that in solutions of these compounds both tautomers are present. 

P.O.67 is a member of the pyrazolo-quinazolone pigment series. Its constitution is listed in the Colour Index under Constitution No. 12915. Coupling component is the heterocycle shown on p. 503. The diazonium component is 2-nitro-4-chloroani-line. Coupling affords the pigment, which was found to exhibit the hydrazone structure ... 

NMR studies have confirmed the enol tautomer 19 for the so-called tetrahydroisatins,81 and support the hydrazone structure for N-methylisatin- 3-phenylhydrazone.242... 

Permethylated tosylated a-cyclodextrin was coupled with aminohydroxyazo-benzene. The product was dimerized to Janus [2]pseudorotaxane, which in turn was bis-azo coupled with 2-naphthol-3,6-disulfonic acid. The product undergoes selfassociation as shown in Figure 14 [44], Note that the final product has o-quinone hydrazone structure. 

Common Name Mesityl oxide (1-phthalazinyl) hydrazone Structural Formula ... 

An early transition state is commonly assumed for exothermic radical addition reactions, and this enables approximation of the transition state geometry based on the ground-state structure. From this assumption, we hypothesized that a substituent above or below the plane of the C=N bond in the ground state hydrazone structure... 

A. A. Akhrem, A. M. Moiseenkov, M. B. Andaburskaya, and A. J. Strakov, J. Prakt. Chem. 314, 31 (1972). However, the at first sight more reasonable hydrazone structure is not ruled out, according to preliminary results from the laboratory of the Editors. 

Dichlorophthalazine-5,8-dione was obtained in low yield by oxidative chlorination of 5-aminophthalazine (86JMC1329). 1,4-Naphthoquinone reacts with hydrazine to give a black compound, for which the structure of a pentacyclic quinone (289) was establisheii (67T2911). The compound is identical with the product from treatment of binaphthoquinone with hydrazine and for which a hydrazone structure was postulated previously (39CB1623). 

It was found that compounds 39 and 42 exist almost completely as the tautomeric azo forms whereas compound 40 is completely in the hydrazone structure, and compound 41 exists predominantly in the hydrazone form. In that way, the annelation of the benzene ring in the active component has, contrary to the annelation of the benzene ring in the passive component, practically negligible influence on the azo-hydrazone equilibrium . 

The smaller coordination shift for the 15N nucleus in [73c] is consistent with its lone pair of electrons remaining free, whereas they are used for the coordination of the 15N atom in [73b]. The possibility of hydrazone structures [72] contributing to the molecule, rather than the azo-forms [73], is excluded on the basis that the hydrazine nitrogen... 

The hydrazone structure was preferred because of the ease with which S,S -dialkylation of N-aryl dithiocarbazates is known to take place and because acid hydrolysis of the product yields 1,3-dithio]sn-2-cne (CCXXIV) and the aryl hydrazine. The hydrazone (CCXXIII, R2=1 3=R.i=1 5 =H, Ri=CfiH5), independently prepared from 2-imino-1,3-dithiolane (CCX X. V ) 374 and phenylhydrazine 254), has the same melting point (94° C) and causes no lowering of the melting point when mixed with the product prepared from N-phenyl dithiocarbazate and 1,2-dibromoethane (m.p. 

The structure of sugar phenylosazones, derivatives first prepared by Fischer in 1884, has remained undefined. Besides Fischer s open-chain structure, a tautomeric azo-hydrazone structure and ring structures have been proposed. Although work in the last two decades involving ultraviolet spectra studies - and examination of the acetylated - and... 

Reactions of cyclic and acyclic 1,2,3-triones with phenylhydrazine give rise to mono- and bis-(phenylhydrazones). The central carbonyl group of a vicinal tricarbonyl system is electron-deficient and highly electrophilic,255 which is why treatment with an aryldiazonium ion affords 2-phenylhydrazones. The structure of such bis(phenylhydrazones) as cyclopentane-1,2,3-trione 1,3-bis(phenylhydrazone), dehydroascorbic acid 2,3-bis(phenylhydrazone), and cy-clobutanetetraone l,3-bis(phenylhydrazone) has been studied by UV, IR,1H-, 13C-, and 15N-NMR spectroscopy.265-268 Quantum-mechanical calculations to predict the most stable tautomeric forms of some 1,2- and l,3-bis(phenylhydrazones) revealed that the chelated bis(hydrazone) structure was usually more stable than the azoene-hydrazine structure.269-271 This does not mean that such structures do not exist, for example cyclobutanetetraone l,2,3-tris(phenylhydrazone) exists in a stable phenylazoene-hydrazine structure (see 49 Scheme 8).257-263... 

In contrast to the formation of an osazone from phenylhydrazine and the 2-bromo-2-deoxy-hexoses derived from the adduct of tri-O-acetylglucal with bromine, two isomeric products [jwhich were assigned the D-threo-3,4-diacetoxytetrahydro-2-furaldehyde (p-nitrophenyl)hydrazone structures (21)] were isolated from the reaction between 3,4-di-0-acetyl-2-bromo-2-deoxy-D-tAreo-pentose (20) and (p-nitrophenyl)hydrazine. The... 

The Occurrence of True Hydrazone Structures in the Sugar Series, M. L. Wolfrom and Clarence C. Christman, J. Amer. Chem. Soc., 53, 3413-3419 (1931),... 

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