Interaction Types in C₆H₅(CH₂)_nOH–CO₂ (n = 0–4) Determined by the Length of the Side Alkyl Chain

C₆H₅(CH₂)_nOH–CO₂ complexes have been investigated using rotational spectroscopy (n = 0–2) complemented by quantum chemical calculations (n = 0–4), which implies that the side alkyl chain length can determine the types of intermolecular interactions. Unlike the in-plane C···O tetrel bond in phenol–CO₂, the π*_CO2···π_aromatic interaction has been shown to link CO₂ to phenylmethanol and 2-phenylethanol, which is, to the best of our knowledge, the first time it has been demonstrated by rotational spectroscopy. Further elongations of the side alkyl chain gradually increase the energies of intramolecular hydrogen bonds in 3-phenylpropanol and 4-phenylbutanol so that CO₂ cannot break it. CO₂ will be pushed farther from the monomers and link with the -OH group through a dominating C···O tetrel bond. Our observations would allow, with the choice of the proper length of the side alkyl chain, new strategies for engineering C···π_aromatic-centered noncovalent bonding schemes for the capture, utilization, and storage of CO₂.