Appraising the relative strengths of C-H***O[double bond, length as m-dash]C and N-H***O[double bond, length as m-dash]C interactions from cis-N-methylacetamide multimers.
The strength of C-H***O[double bond, length as m-dash]C interactions relative to regular N-H***O[double bond, length as m-dash]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.
Mathieu
Simon
S
Laboratoire de Chimie et Physique Quantique (UMR-CNRS 5626), IRSAMC, Université Paul-Sabatier, 31062 Toulouse Cedex 9, France.
Trinquier
Georges
G