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172 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

primary amino group and one secondary amino group can produce the same

effect as two nitro groups and one nitro group respectively.

In other words one N-hydrogen atom which is able to form a six-membered

ring with one nitro group is sufficient to produce an effect similar to that caused

by two hydroxylic hydrogen atoms.
The difference between the ability of a hydroxyl and an amino group to reduce

the intensity of the maximum produced by a nitro group may be due to the stronger

electron repelling power of amino groups. The much stronger influence of the

amino group may serve (according to T. Urbanski) as one of the arguments that

the hydrogen bond has mainly an electrostatic character.

FIG. 41. Absorption spectra of p-halogen derivatives of β− nitroalcohols, e.g.

[(CH 3 ) 2 CHCH 2 CH(OH)] 2 CXNO 2 : I-X = H, II-X = Cl, III-X = Br (Eckstein,

Sobótka and T. Urbanski [12, 13]).

Eckstein, Sobótka and T. Urbanski [12,13] have also found that in β− halogen

derivatives of β− nitroalcohols, the shape of the absorption curve depends on the

halogen attached to the carbon combined with the nitro group. The increase of

the van der Waals radius of the halogen produces a decrease in the intensity of

the band characterizing the nitro group. The same rule was observed

by the authors when comparing some nitro- and halogenonitro-diols (Fig. 41).

This is probably due to the steric effect of shielding the nitro group by a halogen

atom.

The influence of a solvent on the absorption spectra of nitro compounds has

been examined by several authors. When studying the spectrum of nitromethane,

Bayliss and Brackenridge [14] stated that under the influence of a polar solvent

the nitro group band underwent a hypsochromic shift (Table 21).