Complexes Meisenheimer

The product of this reaction as its sodium salt is called a Meisenheimer complex after the Ger man chemist Jacob Meisenheimer who reported on their formation and reactions in 1902 A Meisenheimer complex corresponds to the product of the nucleophilic addition stage in the addition-elimination mechanism for nucleophilic aromatic substitution... 

A careful study of the reaction of 2 4 6 trinitroanisole with sodium methoxide revealed that two different Meisenheimer complexes were present Suggest reasonable structures for these two complexes... 

Perhaps the most convincing evidence for nucleophilic attack at an unexpected ring position comes from the direct observation of intermediate Meisenheimer complexes in the NMR spectrum. When 2-chloro-3,6-diphenylpyrazine is treated with KNH2 in liquid ammonia, the intermediate (29) was observed directly (Scheme 8). It was postulated that this initially formed complex rearranges to (30) which gives the observed product by elimination of a chloride ion (73RTC708). 

Benzo[6]thiophene, methoxynitro-Meisenheimer complexes, 4, 816 Benzo[6]thiophene, 2-methyl-cycloaddition reactions, 4, 793 protonation, 4, 47 sulfonation, 4, 764 synthesis, 4, 879, 915 Benzo[6]thiophene, 3-methyl-cycloaddition reactions, 4, 793 1-oxide... 

The addition intermediates ean frequently be detected spectroseopically and sometimes ean be isolated. They are ealled Meisenheimer complexes. Espeeially in the case of adducts stabilized by nitro groups, the intermediates are often strongly eolored. 

The benzene anion formed as shown by nucleophilic attack on an aromatic ring is called a Meisenheimer complex. 

Give an expression for the pseudo-first-order rate constant for Meisenheimer complex formation. 

Treatment of l,2-difluoro-3,5-dinitrobenzene with methoxide leads to a single isomer of fluorodinitroanisole. Obtain the energies of the possible Meisenheimer complexes and predict the structure of the product. Is this outcome consistent with the previously-established directing effect of the nitro group ... 

Dinitrobenzofuroxan dissolves slightly in water, giving an acid reaction, and forms a series of explosive - salts which were originally formulated as containing the anion (54). Acidification regenerates the dinitro compound. It has recently been shown that the anion is, in fact, the Meisenheimer-complex (55), on infrared, NMR, and chemical evidence, including the use of 0 and... 

The latter mechanism is characterized by a transition-state structure of type 64 and by its being (in part) analogous to the mechanism at a saturated carbon. The preference of a two-step mechanism to the apparently simpler one-step mechanism is suggested by the isolation of Meisenheimer complexes and by the kinetics of their formation. The experimental evidence on these... 

Meisenheimer complex (Section 16.7) An intermediate formed by addition of a nucleophile to a halo-substituted aromatic ring. 

Meerwein s reagent, 680 Meisenheimer, Jacob, 573 Meisenheimer complex, 573 Melmac, structure of, 1223 Melt transition temperature (Tm), 1215... 

In the first mechanism (equation 74) the nucleophile function attacks the aromatic ring in an ipso-type displacement involving a Meisenheimer complex intermediate243,244, and leads to the rearranged product after expulsion of sulfinate anion (X-). This mechanism should be favoured by the presence of an electron-withdrawing substituent in conjugation with the anion. The second mechanism (equation 75) involves a direct displacement of sulfinate anion (X ) by Y-, without involvement of the aromatic n electrons. 

McLafferty rearrangement 133, 163 Meisenheimer complexes 699, 702 Metal-chelated intermediates 838 Metal-halogen exchange 781, 784 Methionine, oxidation of 852-855 Methionine sulphone 853 Methionine sulphoxide 851-869 reduction of 1063 residues of... 

On heating primary amines react with [3, 13] TNBA to yield intensely colored Meisenheimer complexes. Amino acids also react. 

The y-lactone ring of the steroid skeleton forms an intermediate cardenohde anion in alkaline medium that nucleophilically adds to the 3,5-dinitrobenzoic acid in the position ortho to the two nitro groups. A mesomerically stabilized red-violet anion is produced (Meisenheimer complex). 

The reaction course has not been elucidated (cf. also sodium hydroxide reagent). Hydrolyzation reactions and aromatizations are probably primarily responsible for the formation of colored and fluorescent derivatives. Substituted nitrophenols - e.g. the thiophosphate insecticides — can probably be hydrolyzed to yellow-colored nitro-phenolate anions by sodium hydroxide or possibly react to yield yellow Meisenheimer complexes. Naphthol derivatives with a tendency to form radicals, e.g. 2-naphthyl benzoate, react with hydrolysis to yield violet-colored mesomerically stabilized 1,2-naph-thalenediol radicals. 

Behrend C, K Heesche-Wagner (1999) Formation of hydride-Meisenheimer complexes of picric acid (2,4,6-trinitrophenol) and 2,4-dinitrophenol during mineralization of picric acid by Nocardioides sp. strain CB 22-2. Appl Environ Microbiol 65 1372-1377. 

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