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180 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

The N-O angle for various compounds varies from 125° to 134°, and the

distances between nitrogen and oxygen atoms from 1.17 to 1.30Å

The structural configuration of p- dinitrobenzene was the one most fully examined

in investigations of the structures of aromatic compounds by X-rays. Among the

first to carry out this research were Hertel [41], Bannerjee [42] and James, King

FIG. 44. Electrons density of p- dinitrobenzene(Llewellyn [44]).

and Herrocks [43]. The last group of investigators determined the structure by

means of two-dimensional series and projections onto the principal planes. Be-

cause of limited accuracy attainable with the technique all that time the pattern

obtained was not clear enough. The molecule was not planar, the benzene ring

was distorted, and the N-O, bonds differed in length. It was only when Llewel-

lyn’s investigations [44] were published in 1947, in which a complete three-dimensional

Fourier synthesis was applied, that a definite pattern was obtained as shown in

FIG. 45. Bond distances and angles of p-dinitrobenzene (Llewellyn [44]).

Fig. 44. The accuracy of determination of the bond length was ±0.02Å and that

of the angles ±2°. The molecule proved to be exactly planar with the benzene

ring undistorted, and the lengths of the N-O. bond equal.
The structure of m-dinitrobenzene has been established by X-ray analysis

by Archer [45], utilizing Fourier analysis. The author proved the benzene ring
to be a regular hexagon with sides of 1.41Å. The C-N bonds do not lie in the

plane of the ring but make an angle of 15° with it. The C-N bond length is 1.54Å