Hydrogen bonding in the carboxylic acid-aldehyde complexes

Carboxylic acids have been recognized as important precursor species in atmospheric new particle formation. To clearly understand how aerosols form at the molecular level we investigated the hydrogen bonding interactions in the complexes between carboxylic acids and aldehydes using density functional theory methods. The geometric optimization shows that the Z-type carboxylic acid and aldehyde sub-units are linked together through a classical O-H center dot center dot center dot O and a weak C-H center dot center dot center dot O hydrogen bond, which forms ring structures, and the E-type carboxylic acid and aldehyde subunits are linked through an O-H center dot center dot center dot O hydrogen bond with no ring structure. The binding energies and OH-stretching frequency calculations show that the carboxylic acid (Z)-aldehyde complexes are bonding stronger than the carboxylic acid (E)-aldehyde complexes. In addition, atoms in molecules (AIM) theory and natural bond orbital (NBO) analyses were performed to further interpret the intermolecular properties of the carboxylic acid-aldehyde complexes. This study helps to elucidate the nature of the hydrogen bond in these complexes and reveal their roles in atmospheric new particle formation. (C) 2016 Elsevier B.V. All rights reserved.