Meisenheimer

The very high rate of thiophenoxy substitution, compared with low stability of Meisenheimer-like sulfurated compounds, can explain the simple behavior of the ihiophenoxy-substitution reaction. 

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... 

Rearrangement, Aliphatic amine oxides without an ahphatic hydrogen atom P to the nitrogen undergo Meisenheimer s rearrangement when heated to give trisubstituted hydroxylamines. 

Isoprene (2-methyl-1,3-butadiene) can be telomerized in diethylamine with / -butyUithium as the catalyst to a mixture of A/,N-diethylneryl- and geranylamines. Oxidation of the amines with hydrogen peroxide gives the amine oxides, which, by the Meisenheimer rearrangement and subsequent pyrolysis, produce linalool in an overall yield of about 70% (127—129). 

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... 

MEISENHEIMER N-Oxide Rearrangement Chlormalion at pyridlnes via rearrangemeirt ol N-oxides. 

MEISENHEIMER JANOVSKY Corryilexes The adduct formed from a polynAroaromaiic compourxf in alkaline solution with RO, HO (Melsenheimer) or with acetone (Janovsky)... 

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... 

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