Key indicators Single-crystal X-ray study T = 293 K Mean (C-C) = 0.004 Å R factor = 0.047 wR factor = 0.132 Data-to-parameter ratio = 12.6 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. # 2005 International Union of Crystallography Printed in Great Britain -all rights reserved An X-ray diffraction study of the title compound, C 13 H 15 NO 4 , has demonstrated that the formation of intramolecular O-HÁ Á ÁO C hydrogen bonds

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... s to the lengthening of the carbonyl C O bonds, shortening of the (C )C-O(-H) bond and delocalization of the electron density within the dihydropyridine ring.