NUCLEAR MAGNETIC RESONANCE SPECTRA OF SOME 1-ALKYL-2-PHENYL-3-AROYLAZETIDINES AND RELATED COMPOUNDS . DISPERSION EFFECTS AND CONFORMATIONAL ANALYSIS

Chemical shifts and coupling constants for geminal and vicinal protons of the azetidine ring have been determined for several cis-1-alkyl-2-phenyl-3-aroylazetidines (IVa-f). Similarly, the chemical shifts of azetidine ring protons at C-2 and C-4 have been determined for the corresponding trans-3-deuterioazetidines (V′a-f). The geminal coupling, Ja′b′, from the spectra of V′ and the vicinal coupling, Jc′d′, from the spectra of V were also determined. The observed trend in the chemical shifts is rationalized in terms of a large contribution from intramolecular van der Waals dispersion effects. On the basis of the nmr spectral data of IVa-f, we suggest that the conformation of the azetidine ring is a function of the steric requirement of the N-alkyl substituent, and that the azetidines bearing the smaller N substituents are puckered to a greater extent. Even in the open-chain compounds, 2-[α-(N-triethylcarbinylamino)benzyl]-4′-phenylacrylophenone (IIIa) and the t-butylamino analog (IIIb), deshielding due to van der Waals interactions is apparently important. The preparations and characterizations of 12 new azetidines are described. © 1969, American Chemical Society. All rights reserved.