Molecular rearrangements zwitterion reactions

Under the experimental conditions [TNT] [DBU](I. the rate of formation of the second maximum (468 nm) is slow and the authors could make a quantitative evaluation of the first interaction attributed to the formation of a molecular complex (MC). The low reactivity under these conditions was interpreted as due to the fact that the MC has very little tendency to rearrange to the zwitterionic complex, since the amount of DBU complexed by TNB would be unavailable for the nucleophilic attack. Since in this system the base-catalysed step for departure of TIL does not exist, the small increase in k0bs values with the [DBU] was interpreted as evidence of the mechanism shown in Scheme 16. Similarly, the increase in k with [amine] observed in the reactions of FDNB with butylamine in... 

Organoboranes react with ethyl 4-nitrobenzenesulphonyloxycarbamate under basic two-phase conditions in the presence of benzyltriethylammonium chloride or Aliquat to yield ethyl (V-alkylcarbamates [38]. The reaction probably proceeds via the initial formation of the nitrene, which reacts with the borane to form a B -N+ zwitterion. Subsequent rearrangement and solvolysis leads to the product. Aliquat is the better catalyst for the higher-molecular-weight boranes. 

Nitroarenes are recognized from their characteristic neutral losses due to the NO2 substituent. Normally, all theoretically possible fragment ions, the plausible [M-N02] and [M-O] ions as well as the unexpected [M-NO] ion, are observed. It is worth noting that molecular ions are 1,2-distonic by definition, because nitroarene molecules are best represented as zwitterion (Chap. 6.3). The molecular ion may either dissociate directly by loss of an oxygen atom or a NO2 molecule or it may rearrange prior to loss of NO. For the latter process, two reaction pathways have been uncovered, one of them involving intermediate formation of a nitrite, and the other proceeding via a three-membered cyclic intermediate. [208]... 

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