Abstract: The pharmacological results indicate that the N-monoalkyl substituted (E)-and (Z)-α-halocinnamamidcs display different actions on the central nervous system (CNS-depressant or CNS-stimulant activity). According to the results determined by NMR, the difference in the coupling constants of two olefinic protons (J_E > J_Z) between the two geometrical forms can be used for isomeric assignment for the unsubstituted compounds on the olefinic protons. The value of chemical shifts of β-olefinic H, (δ_H (Z) > δ_H (E)), and NH (δ_H (Z) > δ_H (E)), the difference of which are more than 1 ppm, can be used to distinguish the configuration of α-halocinnamamides^[10]. The coupling constants and β-olefinic proton can be utilized to distinguish α-halocinnamoyl piperidines, because there is no proton on the nitrogen of piperidine ring and the chemical shift difference of β-olefinic H between Z and E form is very small. Because determination is not very easy and has so many interfering factors, these piperidine Z or E compounds can be distinguished by conformation variation of piperidine^[11].
Comparing the aromatic parts of ¹H-NMR spectra of the whole series of α-halocinnamamides, we discovered that the chemical shifts and spectral patterns of aromatic protons are very different between Z and E, due to the difference in stcric-hindrance. Thus this method can be used to distinguish Z or E configuration of α-halocinnamamides.

Key words: NMR, α-halocinnamamidc, Chemical shift, Coupling constant, Configuration