Azide ions defined

The selectivity relationship merely expresses the proportionality between intermolecular and intramolecular selectivities in electrophilic substitution, and it is not surprising that these quantities should be related. There are examples of related reactions in which connections between selectivity and reactivity have been demonstrated. For example, the ratio of the rates of reaction with the azide anion and water of the triphenylmethyl, diphenylmethyl and tert-butyl carbonium ions were 2-8x10 , 2-4x10 and 3-9 respectively the selectivities of the ions decrease as the reactivities increase. The existence, under very restricted and closely related conditions, of a relationship between reactivity and selectivity in the reactions mentioned above, does not permit the assumption that a similar relationship holds over the wide range of different electrophilic aromatic substitutions. In these substitution reactions a difficulty arises in defining the concept of reactivity it is not sufficient to assume that the reactivity of an electrophile is related... 

Nitrilium ions are generally indicated as discrete intermediates in the Beckmann rearrangement of oximes (equation 37, Y = OH2) and in the Schmidt rearrangement (equation 37, Y = N2) of ketones and aldehydes with hydrogen azide. The first stage of these reactions has been defined as an ionization by rearrangement process through a transition state of type 183 (Smith, 1963). 

Although the mechanism of this reaction has yet to be fully established certain of its aspects have been defined. The intermediacy of the anion 269 is very probable, particularly since a solid which is presumably the intermediate (269 R = CgHs) has been isolated from the reaction of anilide ion with p-toluenesulphonyl azide. In support of the structural assignment this solid gave a mixture of phenyl azide (40%) and aniline when heated. The reaction sequence has been summarized as shown in equation (139). 

Two different groups of polymeric structures with nicotinate ions can be defined those containing additional neutral ligands, such as H2O, aromatic diamines, etc., and those with anionic ligands such as halides, thiocyanate, azide or nitrate. 

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