Unusual H‐Bond Topology and Bifurcated H‐bonds in the 2‐Fluoroethanol Trimer

Abstract

By using a combination of rotational spectroscopy and ab initio calculations, an unusual H-bond topology was revealed for the 2-fluoroethanol trimer. The trimer exhibits a strong heterochiral preference and adopts an open OH⋅⋅⋅OH H-bond topology while utilizing two types of bifurcated H-bonds involving organic fluorine. This is in stark contrast to the cyclic OH⋅⋅⋅OH H-bond topology adopted by trimers of water and other simple alcohols. The strengths of different H-bonds in the trimer were analyzed by using the quantum theory of atoms in molecules. The study showcases a remarkable example of a chirality-induced switch in H-bond topology in a simple transient chiral fluoroalcohol. It provides important insight into the H-bond topologies of small fluoroalcohol aggregates, which are proposed to play a key role in protein folding and in enantioselective reactions and separations where fluoroalcohols serve as a (co)solvent.

A Direct Link from the Gas to the Condensed Phase: A Rotational Spectroscopic Study of 2,2,2‐Trifluoroethanol Trimers

“…[24] III,o n the other hand, exhibits an unusual H-bonding topology where the cyclic O À H···O À Hr ing opens up to accommodate an OÀH···FÀCb ond, similar to that observed for the FE trimer (see below). [19] Based on the good agreement between the predicted and experimental rotational constants and predicted and relative intensities of the a-, b-a nd c-type transitions,one can confidently assign the three observed sets of transitions to conformers I, II,and III.Simulated spectra of I, II,a nd III are compared to an experimental spectrum in Figure 1. In the simulation, we scaled the relative abundances of I, II,a nd III to 16:1:1 to best reproduce the relative experimental intensities.S ince I consists of one t and two g-TFE subunits whereas II and III are made of only g-TFE subunits,t he abundance of t:g is % 30:70 in aj et expansion, compared to 40:60 in the liquid phase.S urprisingly,e ven at this small cluster size, t-TFE is already an important constituent.…”

“…Examples are the trimers and tetramers of difluoromethane, [17] and the trimers of phenol [18] and 2-fluoroethanol (FE). [19] Here,w er eport adetailed FTMW spectroscopic and ab initio study of several conformers of the TFE trimer. Our study reveals its interesting H-bond topologies,more importantly the appearance of t-TFE, and the significant roles which the O À H···F À CH-bonds and C À F···F À Cc ontacts play in stabilizing the trimer containing the t-TFE subunit.…”

Trendbericht Physikalische Chemie 2017: Atomare und molekulare Tunnelprozesse

“…84) metrische Induktion durch isotope Markierung mit schweren Atomen wie 14 109) Benzosäure-Monohydrat 110) und das Trimer des Fluorethanols. 111) Weitere Tunnelsysteme wurden durch Tieftemperatur UV-Vis-und NMR-Spektroskopie untersucht mit dem Ziel, den Einfluss der Polarität auf die Isomerisierung von Carboxylaten und ähnliche Phänomene zu verstehen. 112,113) Anstrengungen wurden unternommen, die Mikrowellen-und Ferninfrarotspektren von H 2 O-Clustern in der Theorie zu verstehen.…”

Preise 2016 des Chemical Institute of Canada und der Canadian Society for Chemistry

“…Ihr Forschungsschwerpunkt ist die Charakterisierung intermolekularer Wechselwirkungen, die für die Erkennung und den Transfer von Chiralität wesentlich sind. Ihre Arbeit über die H‐Brücken‐Topologie im 2‐Fluorethanol‐Trimer wurde auf einem Titelbild der Angewandten Chemie vorgestellt …”