Key indicators Single-crystal X-ray study T = 293 K Mean '(C±C) = 0.003 A Ê R factor = 0.054 wR factor = 0.177 Data-to-parameter ratio = 12.3 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. # 2002 International Union of Crystallography Printed in Great Britain ± all rights reserved The title molecule, C 11 H 11 NO 3 , is nearly planar, with the mean planes through the p-tolyl and maleamic acid groups inclined at an angle of

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... 5 (3) . The glide-related molecules are linked by NÐHÁ Á ÁO and CÐHÁ Á ÁO intermolecular hydrogen bonds, forming in®nite one-dimensional chains, which are assembled to form layers parallel to the bc plane. Comment The structure of N-(p-tolyl)maleamic acid, (I), was reported previously by Prasad & Sinha (1978) , using photographic X-ray diffraction data, with an R value of 0.16. The structure has now been re®ned using single-crystal X-ray diffraction data and the results are presented here.