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170 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

reason for this is the simultaneous twisting of both o-nitro groups out of plane.

Consequently the conjugation of the two nitro groups with the ring is reduced al-

most to zero.

Methyl groups in nitrotoluenes enhance the conjugation of the nitro groups,

except when they are situated in the ortho position.

The comparison of the absorption spectrum of p- nitrodimethylaniline with

those of its derivatives which substituted with the methyl group in the ortho posi-

tion to the nitro group, according to data reported by Remington [8], (see Fig. 39)

FIG. 39. Absorption spectra of N,N-dimethyl-p-nitroaniline (I) and its methyl deriv-

atives: 3-methyl- (II), 3,5-dimethyl-p-nitrodimethylaniliie (III) (Remington [S]).

is also of interest. The presence of one methyl group does not have a marked

effect upon the absorption spectrum of the nitro group (approx. 260 mμ), but the

presence of a second group causes a considerable fall in the intensity of the band.

Another band produced by these compounds, near 420 mμ, is less affected by

nitro groups.

The influence of aliphatic rings condensed with p- nitroaniline or p- nitrodi-

methylaniline has also been studied (Arnold and Richter [9], Arnold and Craig

[10]). They decrease the intensity of the nitro group band, and also that of a band

near 370-390 mμ.

According to T. Urbanski [l l] the band of cu. 270 mμ the nitro group in aliphatic

compounds can be considerably weakened or it can even disappear under the influ-

ence of hydrogen bonds which link the nitro group with two hydroxyl or one amino

I

group as is shown in schemes Ia and IIa.