Journal of Crystal and Molecular Structure, Vol. 8, No. 4, 1978 Crystal structure of 2-chloroacetamide form): A reinvestigation B. KALYANARAMAN, L. D. KISPERT, * AND J. L. ATWOOD Department of Chemistry The University of Alabama Tuscaloosa, Alabama 35486 (ReceivedApril 28, 1978) Abstract The crystal structure of the ~ form of 2-chloroacetamide, grown by sUb- limation, has been determined from three-dimensional counter data and refined by full-matrix least-squares techniques. The crystals belong to the monoclinic space group P21/c with a = 10.263(8), b = 5.142(5), c =7.458(6) ~, /3=98.72(4)°, and D~=l.60 gcm -a for Z=4. The final R factor for 518 observed reflections is 0.037. The molecule exists as a hydrogen-bonded dimer in the crystal structure. The configuration of atoms C(1), C(2), O, and N is planar to within 0.008 AI, and the CI-C(1)-C(2)-O dihedralangle equals 168 ° . The dimeric hydrogen bonding as well as the CH2 conformation favors the stabilization of a transient oxygen-centered radical. Introduction As part of a general ESR study of the radicals formed in irradiated crystals of carboxylic acids and amides, it was noted that an oxygen-centered n radical, was present in irradiated 2-chloroacetamide at 77 K that was not detected in irradiated 2-chloroacetic acid (Kalyanaraman and Kispert, 1978). Based on previous studies of irradiated carboxylic acid, this result seemed inconsistent since similar radicals should have been formed (Iwasaki, 1972). Assuming the difference to originate in the crystal structures of the two compounds, the crystal structure of the stable form of 2-chloro- 175 0308-4086/7810800-0175 $ 05.00 [0 © 1979 Plenum Publishing Corporation