urbaf2

178 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

The authors explain that the strong steric effect on o- nitro groups produced

by the halogens, particularly iodine, is superposed upon the induction effect of

the o- nitro groups. Hence a reduction in the frequency of p- nitro group vibrations
occurs. This is in agreement with an observation by Golder and Zhdanov [37] who

TABLE 24

Substances

Asymmetrical Position of the

vibrations, cm-1 nitro group

sym-Trinitrobenzene 1558 o- and p-

1550

Picrylchloride 1560

p-

o-

1543

Picryl iodide 1558 p-o-

found that the C-N bond in the para position in picryl chloride is considerably

shortened (1.38 Å), and thus approaches the value of a double bond. The ortho-

situated C-N bonds are of a normal length (1.46 Å).

In the case of 2,4,6-trinitrobenzoic acid, the frequency of all the nitro groups

remains unchanged (1553 cm-1). However, the presence of nitro groups increases

the C=O frequency of the carboxylic group to 1733 cm-1 (as against 1698 cm-1

TABLE 25

SPECTRAL CHARACTERISTICS OF MONO-, DI- AND TRINITRO COMPOUNDS

Nitro compounds Bands, cm-1

o- Mononitro containing any one of the following groups ortho to the nitro:
CH 3 , C 2 H 5 , CHO, NH 2 , COOH

787-781

p- Mononitro containing the same group as above para to the nitro^1111

m- Dinitro containing the following additional group: CH 3 , C 2 H 5 , OH, 930-922†
NH-NH 2 , COOH, CHO. OCH 3 , CH 3 NH, C 2 H 5 NH, NO 2 (trinitro) in
sym-trinitro compounds 939-909

m- Dinitro containing other additional groups ortho to the nitro 840-836

sym-Trinitro which have the additional groups: CH 3 , C 2 H 5 , OH, OCH 3 ,
OC 2 H 5 , COOH, NH

† These bands are the most important for diagnostic purposes.

1081†