Interaction with Carboxylic Acid and Ester

The energetics, too, illustrate the cooperative nature of the two H-bonds. As reported in Table 2.48, the formamide and formic acid molecules are bound together in the cyclic complex by some 12.6 kcal/mol at the MP2/DZP level. The (OH--0) H-bond of structure (b) contributes 7.0 kcal/mol while 3.8 kcal/mol more arises from the (NH 0) interaction. Together, these two separate H-bonds add up to less than the full interaction in the cyclic structure. (Structures (b) and (c) do not represent true minima on the potential energy surface.) It is interesting to note that correlation plays little apparent role in the computed binding energies of this particular complex. 

The studies of formic acid and formamide suggest that the CH group can act as a proton donor. While there is some question as to whether it constitutes a true H-bond, there are clearly certain stabilizing interactions present. 

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