The role of secondary interactions on the preferred conformers of the fenchone–ethanol complex

Abstract

Three conformers of the complex formed between fenchone, a natural common odorant, and ethanol, a mimic of serine's side chain, have been identified using high resolution rotational spectroscopy. All conformers show a main O⋯H–O hydrogen bond and C–H⋯O secondary weak interactions, which drive the relative arrangement of the two moieties.

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

“…Although for the ethanol monomer the trans form (EtOH t ) is more stable than the gauche conformer (EtOH g ), both species are observed in complexes. A preference for the EtOH g conformer is observed for complexes where ethanol interacts with partners through additional weak attractive interactions next to the hydrogen bond . In the acetone–EtOH system, for example, only the EtOH gauche complex was observed, which was attributed to relaxation processes between the trans and the gauche complexes .…”

Binding Site Switch by Dispersion Interactions: Rotational Signatures of Fenchone–Phenol and Fenchone–Benzene Complexes

“…This arrangementc ontrasts with the preferred binding site of the 1:1c omplexes of fenchone with water [17] and ethanol. [15] In these two complexes, water and ethanol locate themselveso nt he other side of fenchone, with their -OH groups in the plane bisecting the C9-C1-C10 angle and binding through OÀH•••O hydrogen bonds to the oxygen in fenchone (see Figure S5 in the Supporting Information). This arrangement is similart ot hat in FPHE2 (Figure 1) and allows full overlap of the -OH group of phenol with the carbonyl oxygen lone pair.I nF PHE1, the C8 methyl group of fenchone forces the OÀH•••O bond to be out-of-plane, thereby weakening the hydrogen bond and decreasing electrostatic contributions.…”

“…This was also observed for the fenchone-ethanol complex. [15] There are considerable discrepancies between the B3LYP-D3BJ and MP2 predictions, which are discussed in the following sectioni nt he context of competing intermolecular interactions.…”

“…The structures of odorant receptors and odorant binding sites have not been resolved, [8] but modelling studieshavepredictedt he existence of hydrogen bonding and hydrophobic (dispersive) interactions mediated by the amino acid residues of serine, tyrosine and phenylalanine, among others. [9][10][11][12] We have started investigating the interactions of common odorants with mimics of amino acid residues and recently reported the interactions of the odorant fenchone, present in natural essential oils [13,14] and widely used in household products, with ethanol, [15] chosen as am imic of the side chain of serine. Fenchoneh as ar igid structure, [16] whichm akes it easier to analyse its interactions with different partnersa si ts conformational flexibility does not need to be considered.…”

“…The presence of an aro-matic ring introduces the possibility of forming CÀH•••p interactions andc hanges the potential dispersion interactions. Benzene sharest he presence of an aromatic ring with phenol but lacks an -OH group, which allows us to determine the influence of not having as trong OÀH•••O hydrogen bond on structural preferences.P henola nd benzene are models for tyrosine and phenylalaniner esidues, respectively.B ys tudying their complexes,a nd comparing them with those of fenchone with ethanol [15] and water, [17] we will obtain information on the interplay between the different hydrogen-bonding and dispersion interactions.…”