Nitration of substituted benzenes is a frequent experiment in the undergraduate organic curriculum. 4-Methylacetanilide gives only the 2-nitroproduct showing the acetamido group is a more powerful o-, p- director than methyl. In 1885, Gatterman observed that the m.p. of the product varied with the solvent used for crystallization, one white (m.p. 94-95o) and one yellow with m.p. 116o. Polymorphism has become a hot topic in the study of pharmaceuticals with the finding that the efficacy of certain drugs depends not only on chemical identity but also on the crystal structure of the product. As a result 4-methyl-2-nitroacetanilide has had its structure studied by X-ray crystallography and solid state NMR. The white and yellow polymorphs were distinguished by inter vs intramolecular H bonding. In previous studies of 2-nitroacetanilide we observed that the 1H and 13C NMR spectra was quite different in CDCl3 and DMSO-d6. It seems polymorphism can exist in solution as well as in the solid state. We are looking at 4-methyl-2-nitroacetanilide for the same type of evidence in solution as is found in the solid state. In addition, 2-nitroacetanilide also forms polymorphic crystals.

Polymorphism in solution observed by NMR spectroscopy

247th National Meeting (2014)

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