urbaf2

AROMATIC NITRO COMPOUNDS^223

He also studied the effect of the solvent and found that it should not be neg-

lected :

Heats of formation

in CC1 4 in C 2 H 2 Cl 4

anthracene-m-dinitrobenzene 2.2 kcal/mole 1.5 kcal/mole

anthracene-sym-trinitrobenzene 4.4 kcal/mole 3.6 kcal/mole

Ross and Labes [I34] determined the heats of formation of the addition com-

pounds: 1,3,5-trinitrobenzene-naphthalene and -aniline, and found them to be

3.3 and 5.1 kcal/mole respectively.

According to Kross and Fassel [135], addition compounds between nitro com-

pounds and amines can be formed through hydrogen bonds of the type:

This was based on the shift in frequency of the nitro group bands in the infra-
red absorption spectrum.
It has also been suggested that 1,3,5-trinitrobenzene and m- dinitrobenzene
may react with amines to form addition compounds by a proton transfer reaction
(Lewis and Seaborg [136], Farr, Bard, and Wheland [137]).
However, Field, W. G. Garner and Smith [138] had concluded earlier that proton
transfers do not occur in liquid ammonia solutions of m- dinitrobenzene. On the
basis of ultra-violet and visible absorption spectra and electrical conductance
measurements of the products of interaction of polynitroaromatic compounds
with a variety of amines, Miller and Wynne-Jones [139] came to the conclusion
that:
(a) Proton transfers do not appear to be involved in the formation of com-
plexes by 1,3,5-trinitrobenzene but electron transfers probably occur.
(b) Both proton transfers and electron transfers occur when 2,4,6-trinitro-
toluene and 2,4,6-trinitro-m-xylene react with amines.
Steric factors in addition compounds also ought to be referred to when con-
sidering formation of addition compounds. X-ray diffraction studies (e.g. Powell
and Huse [115], Rapson, Saunder and Stewart [116]) have shown that in general
the crystalline addition compounds consist of alternate layers of the two components.
The approach of the acceptor molecule can be sterically hindered if the donor
molecule is non-planar. Hence complex formation is difficult as the non-planarity
increases the distance between the components. For example, trans-stilbene forms
a picrate, but the cis-isomer does not. The planar molecule of 2-phenylnaphtha-
lene also forms a picrate, while its non-planar isomer, 1-phenylnaphthalene, fails
to do so.
Hammick and Sixsmith [140] found that indene (X) and dimethyl-4,6,4’,6’-tetra-
nitrodiphenate (XI) formed an addition compound at a relatively low rate, which

could be measured.