Appraising the relative strengths of C-H***O=C and N-H***O=C interactions from cis-N-methylacetamide multimers
Résumé
The strength of C-H***O=C interactions relative to regular N-H***O=C hydrogen bonds is estimated from DFT quantum calculations on multimers of cis-N-methylacetamide (NMA). Assuming transferable hydrogen-bond increments, treatment of various constraint-free NMA dimers and trimers enables us to provide statistical values for (i) the direct energy difference between the two kinds of interaction (calculated around 5 kcal mol(-1)), and (ii) their associated binding energies, hence the ratio of their strengths. Combining the binding energies with other critically-analyzed observables, a relative strength of about 20%-say no more than one fifth-is finally proposed.