On the polarity of the amide group and its impact on dipeptide conformation

Abstract Giving explicit consideration to the lone pairs of the carbonyl oxygen of the amide group it is found that the polarity of the amide group resides essentially in the lone pair. As a confirmation, the lone pairs of the ester group are also found to account for most of its polarity. This localization of amide dipole affects the dipeptide conformation map only in the unallowed regions of the map, but has significant impact on the dipole moment of the dipeptide in different conformations. The experimentally observed dipole moments of dipeptides in solution are in conformity with our assignment of polarity of the amide group.