Migration aptitude

The migration aptitude iacreases ia the foHowiag order secondary alkyl < primary alkyl < allyl, ben2yl. 

For the reaction shown below the migration aptitudes appear to decrease in the order H> >CH8 86 But there may be a special chain mechanism for H. 

The rearrangement of IV-triarylmethylhydroxylamines gives the migration aptitudes -anisyl > phenyl > -chlorophenyl > -nitrophenyl.87... 

The acid catalyzed rearrangements of peroxides, in which the migrating groups show the same migration aptitudes as in carbonium ion rearrangements, may be represented as rearrangements of oxygen cations.89-91... 

In the presence of ferrous salts the hydroperoxide decomposition goes by way of an oxygen monoradical intermediate, with different migration aptitudes. Para nitrophenyl rather than phenyl migrates under the radical conditions. Although the oxygen cation resembles the carbonium ion both chemically and in charge type, it may also be a diradical ... 

The decomposition of the peroxide IX, which gives acetophenone when the conditions are such as to favor the radical mechanism, gives methyl ethyl ketone if the reaction is run in acid. This is because of the superior migration aptitude of phenyl groups in real or incipient oxygen cations.112... 

The decomposition of t.ert-bvA.y triarylmethyl peroxides is particularly well suited to the measurement of migration aptitudes in oxygen radicals because the nature of the product leaves no doubt that the reaction is in fact a rearrangement rather than a /9-cleavage. 

In cases where the pertinent configuration is a transition state rather than an intermediate, the importance of a charge-accepting structural feature will depend on the degree to which a charge is actually developed in the transition state. This means that even on electronic grounds alone it is not certain that migration aptitudes should be independent... 

Since it is not always known to what extent the departing group is still present at the rearrangement stage of the reaction, a detailed interpretation of migration aptitudes is difficult. The examples just discussed, however, should certainly not be compared with migration aptitudes within a fully formed carbonium ion. 

In the mildest of these reactions the hydroxylamine is refluxed in ether over phosphorus pentachloride and the same order of migration aptitudes is observed as in the pinacol rearrangement. The range in... 

In at least the first three of the high temperature reactions the migration aptitudes are not quite those to be expected of the analogous... 

The migration aptitudes in the reaction of ketones with peracetic acid in acetic acid as a solvent are in the order -anisyl > phenyl > >-nitro-phenyl.82 Cyclohexyl and phenyl are about equal in migration aptitude... 

The abnormal ozonolysis is chiefly observed when the group R is one that shows a high migration aptitude in carbonium ion rearrangements. 

The last reaction shows that the benzyl group has a superior migration aptitude in the Stevens rearrangement. It is more reactive in nucleophilic... 

The interplay of crystal packing, migrational aptitudes, and solid-state reactivity maybe demonstrated with the reactivities of the Diels-Alder cycloadducts of maleic anhydride and cyclopentadiene (1 and 2) or cyclohexadiene (3). 

In the case of unsymmetrical glycols the product formation depends mainly on which OH group is lost to leave behind the most stable carbocation, and thereafter which group migrates. The order of migrating aptitude is Ar > H > R. 

Table 2. Kinetic data for the thermolysis of -XC8H4(C6H5)2CN3 in dibutyl carbitol and migration aptitudes in absence of solvent ...

---