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This contribution describes the synthesis and structural investigation of the symmetric and nonsymmetric oxamides N,N Ј-bis(2-hydroxyphenyl)oxamide 1, N,N Ј-bis(5-tert-butyl-2-hydroxyphenyl)oxamide 2, N,N Ј-bis(3,5-dimethyl-2-hydroxyphenyl)oxamide 3, N,N Ј-bis(2-hydroxybenzyl)oxamide 4, N,N Ј-diphenethyloxamide 5, N-(2-hydroxyphenyl)-N Ј-(2-methoxyphenyl)oxamide 6, N-(2-hydroxyphenyl)-N Ј-phenethyloxamide 7, (1S,2R)-(؊)-N-(2-hydroxyphenylcarbamoylcarbonyl)norephedrine 8, (1R,2S)-(؊)-N-(2-hydroxyphenylcarbamoylcarbonyl) 9, ethyl N-(2-hydroxyphenyl)oxalamate 10 and ethyl N-(2-methoxyphenyl)oxalamate 11. The structures were established by 1 H, 13 C, 15 N and variable temperature NMR spectroscopy. Compounds 1-4 and 6-11 are stabilized by intramolecular three-center hydrogen bonding between the amide proton and two oxygen atoms. The 1 H NMR / T value of the amide proton correlates with the 15 N NMR chemical shift. The X-ray diffraction molecular structures of 1 and 11 showed a planar conformation with trans configuration in the solid state, corresponding to the preferred conformation found in solution.

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The structure and conformation of N,N'-bis[(2-hydroxy)phenyl]oxamide (1 ); N,N'-bis[(2-methoxy)phenylloxamide (2); NN-bis(pheny1)oxamide (3); N,N'-bis[(l R,2S)-( -)-norephedrineloxamide (4); N,N'-bis[ (1 R,2R)-( -)-norpseudoephedrine]oxamide ( 5 ) ; N-[(2-hydroxy)phenyl]methylamide (6); N-[ (2-methoxy)phenyl]methylamide (7); N-phenylmethylamide (8); N-[ ( -) -norephedrine1methylamide ( 9 ) and N-[( -) -norpseudoephedrine]methylamide (1 0) were unambiguously established by 'H, 13C, 15N, 2 0 and variable temperature NMR spectroscopy. A careful NMR investigation of the conformational behaviour in these systems was relevant. It has been found that the dicarbonylic group in compounds 1-5 has a trans geometry, stabilized by intramolecular hydrogen bonding and that they possess a C2 axis. Compounds 1 and 2 are planar and compounds 1,2,4 and 5 present the amidic proton coordinated by two oxygen atoms.

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