## Abstract

The crystal of meta-dinitrobenzene, C$_{6}$H$_{4}$(NO$_{2}$)$_{2}$, is orthorhombic pyramidal. The dimensions of the unit cell, which contains 4 molecules, are a = 13$\cdot $3 A, b = 14$\cdot $1 A, c = 3$\cdot $80 A and the space group is Pbn. The method of double Fourier series has been applied, and a projection of the electron density on the ab plane has been made. The plane of the benzene ring of the molecule is inclined at an angle of 20 degrees to the b-axis, and is parallel to the a-axis. Within the limits of experiment, the benzene ring is a regular hexagon of side 1$\cdot $41 A. The C$\chembond{1,0} $N links do not lie in the plane of the ring, but make an angle of 15 degrees with it. The C-N distance is 1$\cdot $54 A, the N-O distances have been assumed the same, 1$\cdot $20 A, and the O-O distance is 2$\cdot $17 A. The closest approach of O to CH in adjacent molecules is about 3$\cdot $0 A, that between O and O about 3$\cdot $2 A, and that between CH and CH is 3$\cdot $8 A. A discussion of the packing of the molecules in the structure is given.