Appraising the relative strengths of C–H⋯OC and N–H⋯OC interactions from cis-N-methylacetamide multimers

Abstract

The strength of C–H⋯OC interactions relative to regular N–H⋯OC 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.