In 4,6-disubstituted N,N'-(1,3-phenylene)bispivalamides,
the ring hydrogen between the two amide groups is deshielded by both and
consequently shows its 1H nuclear magnetic resonance at extremely
low field. Preferential stabilization of a particular amide configuration by
dipole-dipole interactions gives rise to differential shielding effects in
N,N'-(4-chloro-1,3-phenylene)bispivalamide and to strong deshielding of the
aromatic C5-H in N,N'-(2-methylthiopyrimidine-4,6-diyl)bispivalamide.
