Isomers, proportions

TABLE 4.2 Nitration of aromatic compounds isomer proportions and partial rate factors ... 

Substituents in pyridinium salt Relative rates Isomer proportions (partial rate factors) i 0 p-ratio... 

Cation Nitrating sjstemf Isomer proportions % Rate constantst/l mol s PartiaJ rate factors Ref. 

These isomer proportions were obtained for nitration with nitric acid at 0 to... 

II For the conditions under which the isomer proportions were determined the original paper should be consulted. ... 

Compound Nitrating system Isomer proportions/% 2/1 moF s t Relative rate /<, fm io p- ratio i tn p ratio Ref. 

I The rate constants given refer to the acidities quoted, but the accompanying isomer proportions usually refer to slightly different acidities. However, as noted, isomer proportions are not much affected by changes in acidity. Rate profiles are available for all of the compounds. ... 

The isomer proportions for the nitration of the chlorotoluenes, to be expected from the additivity principle, have been calculated from the partial rate factors for the nitration of toluene and chlorobenzene and compared with experimental results for nitration with nitric acid at o °C. The calculated values are indicated in brackets beside the experimental values on the following structural formulae. In general, it can be... 

The nitration of phenylpyridines and related compounds has attracted attention for a long time, and measurements of isomer proportions have been made for several compounds of this type. Nitration occurs in the phenyl ring. For 2-phenylpyridine and 2-phenylpyridine i-oxide measurements of the dependence of rate of nitration upon acidity in 75-81 % sulphuric acid at 25 °C show that both compounds are nitrated as their cations (table 8.1). The isomer distribution did not depend significantly upon the acidity, and by comparison with the kinetic data for quinolinium ( 10.4.2) the partial rate factors illustrated below were obtained.They should be compared with those for the nitration of 2-nitrobiphenyl ( 10.1). The protonated heterocyclic groups are much... 

The first quantitative studies of the nitration of quinoline, isoquinoline, and cinnoline were made by Dewar and Maitlis, who measured isomer proportions and also, by competition, the relative rates of nitration of quinoline and isoquinoline (1 24-5). Subsequently, extensive kinetic studies were reported for all three of these heterocycles and their methyl quaternary derivatives (table 10.3). The usual criteria established that over the range 77-99 % sulphuric acid at 25 °C quinoline reacts as its cation (i), and the same is true for isoquinoline in 71-84% sulphuric acid at 25 °C and 67-73 % sulphuric acid at 80 °C ( 8.2 tables 8.1, 8.3). Cinnoline reacts as the 2-cinnolinium cation (nia) in 76-83% sulphuric acid at 80 °C (see table 8.1). All of these cations are strongly deactivated. Approximate partial rate factors of /j = 9-ox io and /g = i-o X io have been estimated for isoquinolinium. The unproto-nated nitrogen atom of the 2-cinnolinium (ina) and 2-methylcinno-linium (iiiA) cations causes them to react 287 and 200 more slowly than the related 2-isoquinolinium (iia) and 2-methylisoquinolinium (iii)... 

Table 10.3. Isomer Proportions in the Nitration of Some Substituted Benzenes ...

Table 6 displays data for the isomer proportions formed in the nitration and halogenation of nitrobenzene224. As with all +/, +R substituents, the formation of the meta isomer predominates. The reactions are far slower than those of benzene itself. Partial rate factors for the reaction of nitrobenzene with HNO3-H2SO4 are as follows / , 1.08 x 10 8 fm,... 

The samples of unknown composition—21-23 and samples 1-20, 24-34 (Appendix I) were those of Aroclors of variable composition. Variables 5-73 are isomer concentrations (Variable 74, the total PCB concentration in ppm was not included in the analysis). Variables 5-73 represent the fractional composition or isomer proportional concentration values. Representative concentration histograms of the data set are presented in Figure 13. Four PLS components were extracted and then used to estimate the Aroclor content of the unknowns and of a standard sample (No. 24). The Aroclor standard is a mixture of three Aroclors in the ratio of 033 0.33 0 0.33. Chromatograms of the samples for which the PLS estimates were made (Table VI) were similar when compared to a chromatogram of a similar mixture of standards. 

Marziano et al., 1977). The use of this value and a value of ken of 7.7 x 109 mol-1 s-1 dm3 at 25 °C (cf. Table 1) gives the rate coefficient for the reaction of benzene with the electrophile as 1.2 x 107 mol-1 s 1 dm3. This is within the range of values found for reaction with the nitronium ion (see above). The assumption that the nitronium ion is the electrophile is also consistent with the relative reactivities and isomer proportions found in compounds that react at rates below the encounter rate (Ridd, 1966 Baas and Wepster, 1972). 

Compound Nitrating system Isomer proportions/ % fe2/l mol-1 s 4t Relative rate fo u h i o p-ratio i m p-ratio Ref. 

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