On the interaction of propynal with HNO, HF, HCl, H2O, CH3OH, and NH3: Red- and blue-shifting hydrogen bonds and tetrel bonds

Abstract

The potential energy surfaces of the complexes of propynal, (propiolaldehyde, propargyl aldehyde, HCCCOH), with a series of small molecules (HNO, HF, HCl, H2O, CH3OH, and NH3) have been investigated theoretically at the MP2 and CCSD(T) levels using several extended basis sets. Thirty low-lying minima have been detected, eight for HCCCOH-HNO, four for each of the dimers HCCCOH-HF, HCCCOH-HCl, and HCCCOH-H2O, seven for the HCCCOH-CH3OH complex, and three for HCCCOH-NH3. The most stable HCCCOH-HNO complex has a non-planar, orthogonal structure with a tetrel bond and a hydrogen bond. In most cases the calculated intramolecular bond length changes as induced by complex formation are allegeable on the basis of the intramolecular harmonic force fields of propynal and the partner molecules. The vibrational frequency shifts, typical for formyl groups engaged in hydrogen bonding, red shifts of CO stretches and blue shifts of CH stretches, occur in most of the dimers, whereas the acetylenic CH and CC stretches are red-shifted when this CH bond is involved in hydrogen bonding. In almost all HCCCOH-HNO complexes, the NH stretching frequency is also blue-shifted. However, in case of the most stable HCCCOH-HNO complex a red-shift of the harmonic NH stretch is calculated. Inclusion of anharmonic contributions reduces this red shift substantially and even converts it to a blue shift. Conventional red shifts of X-H (X = F, Cl, O) stretching frequencies and blue shifts for formyl CH stretches are calculated for most of the complexes with HF, HCl, H2O, CH3OH, and NH3.