3-CENTER INTRAMOLECULAR HYDROGEN-BONDING IN OXAMIDE DERIVATIVES - NMRAND X-RAY-DIFFRACTION STUDY

This contribution describes the synthesis and structural investigation of the symmetric and non-symmetric oxamides N,N'-bis(2-hydroxyphenyl) oxamide 1, N,N'-bis(5-tert-butyl-2-hydroxyphenyl)oxamide 2, N,N'-bis(3 ,5-dimethyl-2-hydroxyphenyl)oxamide 3, N,N'-bis(2-hydroxybenzyl)oxamid e 4, N,N' -diphenethyloxamide 5, N-(2-hydroxyphenyl)-N'-(2-methoxyphen yl)oxamide 6, N-(2-hydroxyphenyl)-N'-phenethyloxamide 7, )-N-(2-hydrox yphenylcarbamoylcarbonyl)norephedrine 8, (1R,2S)-(-)-N-(2-hydroxypheny lcarbamoylcarbonyl) 9, ethyl N-(2-hydroxyphenyl)oxalamate 10 and ethyl N-(2-methoxyphenyl)oxalamate 11. The structures were established by H -1, C-13, N-15 and variable temperature NMR spectroscopy, Compounds 1- 4 and 6-11 are stabilized by intramolecular three-center hydrogen bond ing between the amide proton and two oxygen atoms, The H-1 NMR Delta d elta/Delta T value of the amide proton correlates with the N-15 NMR ch emical shift. The X-ray diffraction molecular structures of 1 and 11 s howed a planar conformation with trans configuration in the solid stat e, corresponding to the preferred conformation found in solution.