The 1-Naphthol Dimer and Its Surprising Preference for π–π Stacking over Hydrogen Bonding

Abstract

Using chirped-pulse Fourier transform microwave spectroscopy, we have experimentally identified the most abundant dimer of an alcohol analogue of naphthalene, 1naphthol. The 1-naphthol dimer features a V-shaped, partially overlapping π−π stacked structure with no canonical hydrogen bonds between the subunits. This structural assignment is in contradiction to an earlier study of the 1-naphthol dimer using UV-IR dip double resonance spectroscopy in the O−H stretch region, which assigns a π-stacked but also canonically hydrogen-bonded structure. We use an improved theoretical analysis to resolve this discrepancy and show that the new, V-shaped structure is also consistent with the previously measured UV-IR data. These new computational and spectroscopic results shed light on the complicated nature of evaluating energetics and structures for larger, dispersionbound systems.

Automated exploration of the low-energy chemical space with fast quantum chemical methods

“…The rotational constants for the seven predicted complexes of the and none of the seven isomers is the most energetically favored complex of the ensemble at the semiempirical level. However, the trend in the aggregate stability identified by Jäger et al, 358 that the V-shaped forms are more stable compared to the stacked and hinge forms is reproduced for the GFN2-xTB ensemble. Comparing directly to the experimental rotational constants (see Tab.…”

“…In fact, the most stable of them is the V-shaped complex that was identified by the authors Ref. 358 and is shown in Fig. 3.23.…”

“…In the literature seven conformations were proposed based on a comparison of the experimental and theoretical rotational constants. 358 With the default NCI-iMTD mode, geometries calculated at a semiempirical level have larger relative deviations compared with geometries calculated by DFT. 359 Therefore, the GFN2-xTB geometries are not expected to reproduce the hybrid DFT rotational constants very well but rather serve as a guideline for the structure evaluation.…”

Rovibronic signatures of molecular aggregation in the gas phase: subtle homochirality trends in the dimer, trimer and tetramer of benzyl alcohol

“…[60][61][62] Strong dispersion interaction between the residues, conformational rigidity and/or steric crowding can also lead to further motifs in which hydrogen bonds are reduced in number and/or strength. Further examples, beyond the already mentioned phenol dimer, are the dimers of 1-naphthol, 63 propofol, 64 3-chlorophenol 65 and racemic (but not enantiopure) methyl mandelate. 66 For benzyl alcohol such structures are calculated to be either high in energy or no minimum at all, and are not observed.…”

Dynamic chiral self-recognition in aromatic dimers of styrene oxide revealed by rotational spectroscopy

“…Here, we report an in-depth structural study centred around chiral self-recognition of SO. We use high-resolution rotational spectroscopy, which provides us definite assignments of complex molecular geometries, including clusters, in the gas phase [44][45][46][47][48][49][50][51][52][53][54][55] . Because of the direct correspondence between the unique moments of inertia of the molecules and their 3D structures, geometries of cluster topologies can be identified from their rotational spectrum and directly compared with theoretical structure calculations.…”