Abstract. C:6H~4NBr, M= 300.20, orthorhombic, Pbca, a=14.207(3), b=16.107(6), c=11.560(4) A, V= 2645 (1) Aa, Z=8, Dx= 1"508, D,,= 1"52 g cm -3. The conventional R was 0.032 for the 1368 reflections [I> 2o'(1)] measured with a Syntex PI diffractometer.The X-ray analysis confirms that the title compound is the product of the cyclization of 3,4-diphenylbut-3-en-2-one oxime benzoate in nitrobenzene solution.Introduction. X-ray diffraction data were measured with graphite-monochromated Mo Kc~ radiation. A crystal 0.34 x 0.39 x 0.44 mm was used. The unit-cell dimensions were obtained from a least-squares fit of the 20, 09, 2' and ~0 values for 15 reflections. A variable speed (1 to 24 ° min -1) 0-20 scan technique was used in measuring all the independent reflections to a maximum 20 of 45 °. The scan range was 1 ° on either side of the e:-e2 peaks. The 1368 reflections with I>2.0a(I) were used in the analysis. The intensities were reduced to a set of structure amplitudes on an