Partial rate factors for nitration

Relative electrophilic localization energies vs. logarithms of partial rate factors for nitration (a) Hiickel, (6) PPP with fixed /3. (From Dewar Thompson. ) (iv) Plot of log K vs. AB c. (From Dewar. )... 

Using the partial rate factors for nitration of chlorobenzene, Ridd and de la Mare calculated the relative rates of nitration of the dichlorobenzenes, with respect to /)-dichlorobenzene, with the results shown below. Also given are results based on more recent nitrations in mixed... 

The partial rate factors for nitration of tert-butylbenzene are... 

All the ring positions of (trifluoromethyl)benzene are deactivated compared with benzene The meta position is simply deactivated less than the ortho and para positions The partial rate factors for nitration of (trifluoromethyl)benzene are... 

From this work the deactivation of pyridine to benzene was estimated as about 107. The partial rate factors for nitration of the 3 position of pyridine and the corresponding pyridinium ion were 101,7-2,5 and 1020 respectively. 2-Phenylpyridine was evaluated as 4.9 x 10"5 times less reactive than benzene. 

The partial rate factor for nitration of pyridine-N-oxide in the 4 position was estimated as 4x 10"6 which is, therefore, close to that found for the 3 position of pyridine, and 2-phenylpyridine-N-oxide was evaluated as 2xl0-4 times less reactive than benzene from rate measurements in 74.7-78.6 wt. % acid at 25 °C. 

RATE COEFFICIENTS AND PARTIAL RATE FACTORS FOR NITRATION OFPhXMe3+ IN... 

Thus for the nitration of toluene by nitric acid in acetic anhydride at 0° kCtHsMJkCiHt was found to be 27, and the isomer distribution (%) o-, 61-5 m-, 1-5 p-, 37 0 the partial rate factors for nitration, under these conditions, are thus ... 

Comparison of the partial rate factors for nitration of toluene with those for chlorination and bromination (above) show that these differ, both absolutely and relatively, with the attacking electrophile in other words relative directive effects in C6H5Y do depend on E as well as on Y. We notice above that the absolute values of the partial rate factors, i.e. fcY//cH, increase in the order,... 

These trends have been quantified for some reactions. Nitration studies showed carbazole to react 222,000 times faster than benzene, with nitric acid-acetic anhydride having partial rate factors of 32,100 (C-1), 1,100 (C-2), 77,600 (C-3), and too small to measure (C-4). Carbazole reacts about 20 times more slowly than diphenylamine. The partial rate factor for nitration at C-3 can be compared with a value of 50,100 found for the perchloric add protodesilylation of 3-trimethylsilylcarbazole. ... 

Fig. 7.1. Nitration of polynuclear hydrocarbons by nitric acid in acetic anhydride, (i) Plot of logio (KJKo) against N. , 9-Anthryl positions A,a-napthyl positions V, 4-phenanthryi positions O, other positions. (From Dewar et a/.286) (ii) and (iii) Relative electrophilic localization energies vs. logarithms of partial rate factors for nitration (a) Hiickel, (6) PPP with fixed p. (From Dewar Thompson.83 ) (iv) Plot of log K vs. AEiac- (From Dewar.23 )...

The quinolinium ion is at least 10s times more reactive in nitration than the pyridinium ion (63JCS4204). The ratio of the reactivity of quinolinium to benzene and to naphthalene has been derived as 1.2 x 10 7 and 1 x 10 l0, respectively [63CI(L)1283 68ZC201], A detailed study of the products of nitration of quinoline by nitric acid in 80 wt% sulfuric acid at 25°C yielded the partial rate factors shown in 11.63 [71 JCS(B) 1254] so that the positional reactivity order for the quinolinium ion is 5 > 8 > 6 > 7 > 3, which is almost exactly that which applies to the free base, although the relative differences are much greater (Section 7). Likewise, partial rate factors for nitration on the isoquinolinium ion are given in... 

The ct+ values show that the position in quinoline should be between 10 and 2 x 106 times less reactive than naphthalene toward nitration. The observed value is 10 °, confirming that, under these conditions, nitration takes place on the conjugate acid and not on the free base [71JCS(B)2382], Likewise, the partial rate factors for nitration of the 5-and 8-positions in isoquinoline require a+ values of 0.77 and 0.92, confirming that reaction takes place on the conjugate acid [75JCS(P2) 1783]. 

These reactions demonstrate not only the strong 7r-donor ability of cyclopropyl but also the conformational dependence of this effect Thus the partial rate factors for nitration of 117 and 119 as compared to the models 118 and 120 reveal that the spiro-cyclopropyl in 117, which is fixed in the bisected conformation, is considerably more... 

Comparable stabilization of the intermediate leading to meta substitution is not possible. Thus, resonance involving halogen lone pairs causes electrophilic attack to be favored at the ortho and para positions but is weak and insufficient to overcome the electron-withdrawing inductive effect of the halogen, which deactivates all the ring positions. The experimentally observed partial rate factors for nitration of chlorobenzene result from this blend of inductive and resonance effects. 

Figure 1. The relationship between the partial rate factors for nitration...

As already discussed, the product distributions and the partial rate factors for nitration do not depend importantly on the character of the supplied reagent. A similar pattern of reactivity is observed for Friedel-Crafts acylation. In both re-... 

TABLE 8.18 Partial Rate Factors for Nitration with Nitric Acid in Nitromethane at 25°C... 

FIGURE 5.31. Plot of logarithms of partial rate factors for nitration of even AHs in acetic anhydride (a) against reactivity numbers AT, (a) against energies of reaction calculated by an SCF MO method [data from (a) Ref. 10 (b) Ref. 3]. 

Nitration.—Whereas a plot of localisation energies versus partial rate factors for nitration of toluene, m- and p-xylene, and mesitylene is curved, other electrophilic substitutions (e.g. halogenation) yield linear correlations. The curvature has been ascribed to a shift of the nitration transition state from resemblance of the intermediate towards resemblance of the reactant with increasing ring substitution. ... 

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