The Crystal-Structure of the Photosynthetic Inhibitors Dcmu and Dtpu

X‐ray diffraction studies have been carried out on a single crystal of the photosynthetic inhibitors N‐(3,4‐dichlorophenyl)‐N′‐dimethylurea (DCMU) and its newly synthesized spin‐labeled analog N‐(3,4‐dichlorophenyl)‐N′‐(3,3,5,5‐tetramethylpiperidine‐4‐oxyl)‐urea (DTPU). The synthesis of DTPU as well as its crystallographic data are reported. The crystal system of both compounds is monoclinic with a space group P 2 1 / c . The cell constants of DCMU are a = 7.759(1), b = 14.737(3), c = 9.233(2) Å, β = 100.99(6)°; of DTPU they are a = 6.976(1), b = 11.998(2), c = 23.585(3) Å, β = 91.38(5)°. Comparison of conformational parameters of DCMU and DTPU reveal differences in the dihedral angle between the aromatic ring and the ureido plane. The measured volumes of DCMU and DTPU are 259.1 and 493.3 Å 3 , respectively. These figures suggest the size of the binding site of the inhibitors in the photosynthetic membrane.