The Crystal Structure of p-Chlorobenzamide - I. High Temperature Modification-

Crystalline p-chlorobenzamide exists in two modifications at room temperature, one is monoclinic with space group P2_1/a and the other triclinic with space group P1^^͡. The latter undergoes a phase transition at about 44℃. The crystal structure of the high temperature modification has been determined from two-dimensional X-ray data. The crystals of this phase are also triclinic with space group P1^^͡. The dimensions of a unit cell containing two molecules are; a=5.05, b=5.55, c=14.6A, α=96.5, β=111.7, γ=95.1°. An approximate arrangement of molecules in a unit cell is obtained by the use of the 'ellipsoid-model method'. It is found that two molecules form a centrosymmetrical dimer, and these dimers are linked by hydrogen bonds into endless chains extended along the a-axis.