Halogens in Acetophenones Direct the Hydrogen Bond Docking Preference of Phenol via Stacking Interactions

Abstract

Phenol is added to acetophenone (methyl phenyl ketone) and to six of its halogenated derivatives in a supersonic jet expansion to determine the hydrogen bonding preference of the cold and isolated 1:1 complexes by linear infrared spectroscopy. Halogenation is found to have a pronounced effect on the docking site in this intermolecular ketone balance experiment. The spectra unambiguously decide between competing variants of phenyl group stacking due to their differences in hydrogen bond strength. Structures where the phenyl group interaction strongly distorts the hydrogen bond are more difficult to quantify in the experiment. For unsubstituted acetophenone, phenol clearly prefers the methyl side despite a predicted sub-kJ/mol advantage that is nearly independent of zero-point vibrational energy, turning this complex into a challenging benchmark system for electronic structure methods, which include long range dispersion interactions in some way.

Sniffing out camphor: the fine balance between hydrogen bonding and London dispersion in the chirality recognition with α-fenchol

“…Geometric parameters, which were found to correlate with differences in OH stretching wavenumbers between isomers of alcohol-ketone complexes, are the hydrogen bond donor attack angle to the carbonyl group a(C2QOÁ Á ÁH) and the outof-carbonyl-plane dihedral angle t(C3-C2QOÁ Á ÁH). [15][16][17] One might amend this with the hydrogen bond linearity angle b(OÁ Á ÁH-O). 68 In RR-A-a-(I), the values of all three angles are closer to their assumed respective optima (a = 1201, t = 01/1801, b = 1801) than in SR-A-b-(I).…”

“…This often energetically subtle isomerism for complexation can be used as an experimental benchmark for the predicted energy difference of electronic structure methods and can be tuned by modification of the donor or the acceptor molecule. [15][16][17] Here, we will also explore whether the preference might be influenced by simple mirroring of either interaction partner. Unlike chemical modifications, this does not change the intrinsic hydrogen bond acceptor or donor quality of the docking sites, therefore exposing geometric consequences from secondary interactions.…”

A litmus test for the balanced description of dispersion interactions and coordination chemistry of lanthanoids

“…The system under study represents a difficult balancing act between dispersion interactions and metal coordination in which pairwise semi-classical approaches like the D-models can lead to misleading results as previously observed, for example, in the study of cryogenic ion vibrational predissociation (CIVP), 133 bond dissociation energies 134 as well as energies, 135 prediction of vibrational spectra 136 and interconversion barriers. 137 We finally note that as shown in this work the inclusion of dispersion corrections, at least via the D3(BJ), D4, and VV10 approaches, although decisive for the description of the interaction energy between the stacked ligandpairs, represents only a necessary but not sufficient condition for an unambiguous prediction of the molecular structures. Therefore, including dispersion corrections of this kind is not always the preferred option when optimizing geometries with DFT.…”

NoisySignalIntegration.jl: A Julia package for uncertainty evaluation of numeric integrals

“…NoisySignalIntegration.jl was developed as a solution to this problem. While the package was developed specifically for the determination of band area uncertainties in the context of molecular spectroscopy (Gawrilow & Suhm, 2021;Karir et al, 2019;Zimmermann et al, 2021), it is applicable in any research area where signals (peaks, lines, bands, etc.) 1 in x-y data need to be integrated and a thorough uncertainty analysis is desired.…”