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CHAPTER XI

NITRO DERIVATIVES OF NAPHTHALENE

GENERAL INFORMATION

NAPHTHALENE is easier to nitrate than benzene, and one or two nitro groups

can be readily introduced into it. The first group enters the α− position, the second

takes the α− position on the ring having no substituents. An isomer with a nitro

group in position 3 to the first one, on the same ring, is also formed in an insignfic-

ant quantity. The introduction of the third nitro group leads to the formation

of several isomers.

Armstrong and Wynne [1] have established an empirical rule :

(a) a further group will not enter a position contiguous to a nitro group;

(b) a further group, other factors being equal, will tend to enter the nucleus

at a position peri to an α− nitro group.

Under drastic conditions of nitration a further nitro group can be introduced

into a naphthalene molecule.

By analogy with the rules of substitution in benzene based on the resonance

theory and by considering that the quinonoid positions in naphthalene relative

to 1 and 2 are 2,4,5,7 and 1,6,8 respectively a less empirical rule of substitution

can be established.

Donaldson [2] gives an example. In 1,8-dinitronaphthalene the 3- and 6-positions

are the least deactivated and nitration leads to 1,3,6,8-tetranitronaphthalene. Where

two positions remain open the α− position shows a greater activity because of the

nature of the naphthalene ring. An anomalous and important case is that of 1,5

dinitronaphthalene, in which only positions 3 and 7 are not deactivated. The main

product of nitration of 1,5-dinitronaphthalene is 1,4,5-trinitronaphthalene and

not 1,3,5- as would be expected. This led Hodgson and Ward [3] to conclude that

the predominant hybrid in 1,5-dinitronaphthalene is

It favours electrophilic substitution in position 4. Modern approach to substitution

rule consist in molecular orbital calculations [45].