Db. Chesnut, The electron localization function signature of the amide bond exhibits nitrogen lone pair character, J PHYS CH A, 104(32), 2000, pp. 7635-7638
An electron localization function (ELF) study of the amide bond at the: B3L
YP/6-31+G(d,p)//MP2(FC)/6-31+G(d,p) level shows that the ELF isosurfaces ne
ar nitrogen resemble those found in planar ammonia where the lone pair is o
f necessity localized on the nitrogen atom. This suggests that in the plana
r form the neutral resonance structure is of considerable importance and gi
ves rise to a characteristic ELF signature for nitrogen in the amide bond a
nd similar settings where the nitrogen lone pair contributes to the bonding
.