London Dispersion and Hydrogen‐Bonding Interactions in Bulky Molecules: The Case of Diadamantyl Ether Complexes

Abstract

Diadamantyl ether (DAE, C20H30O) represents a good model to study the interplay between London dispersion and hydrogen‐bond interactions. By using broadband rotational spectroscopy, an accurate experimental structure of the diadamantyl ether monomer is obtained and its aggregates with water and a variety of aliphatic alcohols of increasing size are analyzed. In the monomer, C−H⋅⋅⋅H−C London dispersion attractions between the two adamantyl subunits further stabilize its structure. Water and the alcohol partners bind to diadamantyl ether through hydrogen bonding and non‐covalent Owater/alcohol⋅⋅⋅H−CDAE and C−Halcohol⋅⋅⋅H−CDAE interactions. Electrostatic contributions drive the stabilization of all the complexes, whereas London dispersion interactions become more pronounced with increasing size of the alcohol. Complexes with dominant dispersion contributions are significantly higher in energy and were not observed in the experiment. The results presented herein shed light on the first steps of microsolvation and aggregation of molecular complexes with London dispersion energy donor (DED) groups and the kind of interactions that control them.

Do Docking Sites Persist Upon Fluorination? The Diadamantyl Ether‐Aromatics Challenge for Rotational Spectroscopy and Theory

“…After geometry optimization, no structures with the aromatic ring interacting directly with the ether oxygen, C−H⋅⋅⋅O or C−F⋅⋅⋅O, were found among the lowest‐energy isomers (Δ E =6.6 kJ mol −1 for DAE‐C 6 H 6 ‐O). This is contrary to the complexes with water and several alcohols, which bind to DAE mainly via hydrogen bonding [21] . The computed rotational parameters for all the possible complexes in these positions are collected in Tables S1–S5.…”

“…The oxygen atom is partially shielded by the two bulky adamantyl moieties, but it influences the electron density in its immediate environment. Hydrogen bonding with the ether oxygen atom, O−H⋅⋅⋅O, was previously observed to be the main interaction for polar molecules R‐OH (R=H, Et, and t Bu) [21] . A conformational search using the GFN‐xTB program [22] suggested that the aromatic ring can interact with the ether oxygen or with any alkyl group from DAE, resulting in about 15 non‐redundant minima for each of the DAE‐aromatic systems.…”

“…Diadamantyl ether is not commercial;i tw as synthesized and characterized as described in ref. [21].Itw as placed in the heatable reservoir of the pulsed nozzle of our spectrometer and heated to ca. 180 8Ct oi ncrease its vapor pressure and thus the number of molecules in the gas phase.…”

“…Hydrogen bonding with the ether oxygen atom, OÀ H•••O, was previously observedt ob et he main interaction for polar molecules R-OH (R = H, Et, and tBu). [21] Ac onformational search using the GFN-xTB program [22] suggested that the aromatic ring can interact with the ether oxygen or with any alkyl group from DAE, resulting in about 15 non-redundant minima for each of the DAE-aromatic systems. During geometry optimizationa tt he B3LYP-D3(BJ) [23a,b] /def2-TZVP [23c] level of theory, three distinct arrangements turned out to be especially favorable for all the systems.…”

“…This is contrary to the complexesw ithw ater and several alcohols, which bind to DAE mainly via hydrogen bonding. [21] The computed rotational parameters for all the possible complexes in these positions are collected in Ta bles S1-S5. In the following, we summarize the rotational spectroscopy analysisf or the three DAE-aromatic speciesa nd discuss their structures and intermolecular interactions based on the spectroscopic and quantum-chemical results.P ortions of the experimentalrotational spectra and the experimental and theoretical rotational parameters are collected in the Supporting Information and in Table 1a nd Ta ble 2, respectively.T he spectrao ft he observedDAE complexes were too weak (vide infra) to observe the singly substituted 13 C-or 18 O-isotopologuesi nn atural abundance,w hich would have provided us with the experimental structureso fthe complexes.…”