Benzene dilution shifts and steric interactions in N,N-dialkylamides

The NMR spectra of ten disubstituted amides have been recorded at 0°C in carbon tetrachloride and in benzene solutions. The benzene dilution shifts (ASIS) and proton spin decoupling were used to make the chemical shift assignments. A time-averaged solvent cluster model for the association between the amide and benzene is consistent with the observed ASIS values. The assignments for the N-methine and N-methyl resonance peaks in RCONCH(CH₃)₂]₂, where R is methyl, ethyl or propyl are inverted from the assignments for N,N-diisopropylformamide (R ? H).