H-1 AND C-13 NMR CHEMICAL-SHIFTS AND N-SUBSTITUENT EFFECTS OF SOME UNSYMMETRICALLY N,N-DISUBSTITUTED ACETAMIDES

The H-1 and C-13 NMR chemical shift assignments of a series of (E)- an d (Z)-N,N-Dialkylacetamides (CH3C(O)NR1R2, with R1/R2 = Me/Et (1), Me/ n-Bu (2), Et/n-Bu (3), Et/t-Bu (4), Ne/Hydroxyethyl (5), Et/Hydroxyeth yl (6), Et/Acetylhydroxyethyl (7)] are reported. The H-1 chemical shif ts for the N-substituents of the amides 1-7 recorded in benzene-d6 and in chloroform-d1 are in agreement with the Hatton and Richards (ASIS) and Paulsen-Todt models, respectively. The C-13 chemical shifts for t he N-substituents of compounds 1-3 were compared with data of the corr esponding symmetrical amides, and the results can be explained by the reciprocal steric compression effect of one N-substituent on the other . The validity of this explanation is confirmed by C-13 spin-lattice r elaxation time (T1) measurements.