Intermolecular amide and aldehyde interactions: rotational spectroscopy of the complexes of formaldehyde with 2-azetidinone and formamide.

The binary intermolecular complexes of amides and formaldehyde can be taken as suitable models to investigate the non-covalent interactions of a peptide with the carbonyl group. We herein studied the rotational spectra of the model complexes of 2-azetidinone-H 2 CO and formamide-H 2 CO generated in a helium supersonic jet. For each complex, one rotational spectra featuring hyperfine structures caused by the 14 N quadrupole coupling effect was observed and assigned to its global minimum conformation. The detected isomers of both studied complexes are stabilized by a dominant amide hydrogen bond N-H⋯OC and a weaker C-H⋯O interaction, preferring the C s symmetry. NBO and SAPT analyses provide quantitative estimation of the non-covalent interactions stabilizing the complexes.