Competitive and cooperative n → π* and n → σ* interactions in benzaldehyde–formaldehyde: rotational characterization

Abstract

The rotational spectrum of the 1 : 1 benzaldehyde–formaldehyde complex has been investigated by pulsed jet Fourier transform microwave spectroscopy combined with ab initio calculations. The two most stable isomers were observed, with the relative abundance ratio N_I/N_II ≈ 3/1 estimated with intensity measurements. Both observed isomers are stabilized by one dominating OC⋯O tetrel bond (n → π* interaction) and one secondary C–H⋯O hydrogen bond. Natural bond orbital analysis and electron localization function analysis were applied to characterize the nature of the noncovalent interactions in the target complex.