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NITRATION THEORIES 69

From these data Wibaut calculated the ratio of the substitution rate influenced

by the CH 3 and Cl groups to be:

CH 3 : Cl = 1 : 1.475

To obtain the ratio of nitration rates when the CH 3 or Cl group was present

alone in a nitrated compound, Wibaut nitrated a mixture of toluene and chloro-

benzene with only a small quantity of concentrated nitric acid. It was found that

contrary to all expectations based on earlier observations, toluene was nitrated

much faster than chlorobenzene. From this it must be concluded that the ratio

of the nitration rates influenced by the two groups present together differed com-

pletely from that when only one of the groups was present in the ring.

Taking that into account, Holleman [55] calculated which isomers were formed

when nitrating bromotoluenes. These calculations were based on the following

experimental data of his own:

(1) the ratio of the isomeric nitrotoluenes, resulting from the nitration of tolu-

ene,

(2) the ratio of the isomeric bromonitrobenzenes, resulting from the nitration

of bromobenzene,

(3) the ratio of the substitution rates influenced by the bromine and the methyl

group present in the benzene ring simultaneously. This was calculated by Holle-

man from the ratios: Cl : Br = 1 : 0.88 (Holleman [54]) and CH 3 : Cl = 1 : 1.475

(given by Wibaut), from which he obtained CH 3 : Br = 1 : 1.3.

Since toluene, when nitrated, yields the ortho- and meta- isomers in the quan-

tities shown in diagram IV, and bromobenzene in those shown in diagram V,

for p- bromotoluene the quantities can be calculated. They are shown in diagram VI.

IV V VI
The percentage is shown in diagram Via. Diagram VIb shows the values found
experimentally. It can be seen that they differ only slightly from the calculated ones: