Collect. Czech. Chem. Commun. 1990, 55, 136-146

13C and 15N NMR spectra of oximes prepared by nitrosation of activated methylene group

Josef Jirmana, Antonín Lyčkaa and Miroslav Ludwigb

a Research Institute of Organic Syntheses, 532 18 Pardubice-Rybitví
b Institute of Chemical Technology, 532 10 Pardubice


15N and 13C NMR spectra have been measured of the compounds type XC(=NOH)Y, where X, Y = COCH3, CN, COOR, CONHR, and X +Y = C6H4(CO)2. The (E)-(Z) isomerism at the C=NOH bond has been studied by means of 15N labelling and stereospecific behaviour of the 2J(15N, 13C) coupling constants. The nitrosation of methyl cyanoacetate gives specifically the respective (E)-oxime, whereas that of acetoacetanilide gives the (Z)-isomer. The nitrosation of ethyl acetoacetate gives both (E)- and (Z)-oximes in a ratio of ca 1:10; the (E)-isomer is less stable and is transformed into the (Z)-isomer. The applicability of the 1J(13C, 13C) coupling constants and lanthanoid shift reagents to the study of (E)-(Z) isomerism of oximes with geminal carbonyl groups has also been verified. The 15N NMR chemical shifts of the oximes studied correlate with their respective pKa values measured in dimethyl sulfoxide according to the equation pKa = -0.11δ15N + 13.44.