Halocarbons as hydrogen bond acceptors: a spectroscopic study of haloethylbenzenes (PhCH₂CH₂X, X = F, Cl, Br) and their hydrate clusters

Abstract

The electronic spectra of 2-bromoethylbenzene and its chloro and fluoro analogues have been recorded by resonant two-photon ionisation (R2PI) spectroscopy. Anti and gauche conformers have been assigned by rotational band contour analysis and IR-UV ion depletion spectroscopy in the CH region. Hydrate clusters of the anti conformers have also been observed, allowing the role of halocarbons as hydrogen bond acceptors to be examined in this context. The donor OH stretch of water bound to chlorine is red-shifted by 36 cm, or 39 cm in the case of bromine. Although classed as weak H-bond acceptors, halocarbons are favourable acceptor sites compared to π systems. Fluorine stands out as the weakest H-bond acceptor amongst the halogens. Chlorine and bromine are also weak H-bond acceptors, but allow for more geometric lability, facilitating complimentary secondary interactions within the host molecule. Ab initio and DFT quantum chemical calculations, both harmonic and anharmonic, aid the structural assignments and analysis.

Thiols as Hydrogen Bond Acceptors and Donors: Spectroscopy of 2-Phenylethanethiol Complexes

“…Thus, Gw 1 must therefore have a structure like is not shifted quite as far as in the analogous 2-phenylethylalcohol cluster ("hydrate F", 3519 cm −1 ), 67 because the sulfur is a slightly weaker acceptor. The ν 3 red-shift is larger than is typically observed in single-donor systems 64,65 but is closer to the analogous PEAL cluster ("hydrate F", 3721 cm −1 ), 67 where water is receiving two weak H-bonds from neighboring aliphatic and aromatic CH groups. In PET, these CH•••O bonds are shorter by ca.…”

“…This produces one mode ( r C2H – r C3H , equivalent to 13 + 7b) that is blue-shifted and another mode ( r C5H – r C6H , or 13 – 7b) that is red-shifted. The predicted separation of 11 cm –1 overestimates the observed experimental splitting, although similar compositional changes have been observed in the anti and gauche conformers of substituted ethylbenzene derivatives benzenepropanenitrile, and haloethylbenzenes …”

“…The predicted separation of 11 cm −1 overestimates the observed experimental splitting, although similar compositional changes have been observed in the anti and gauche conformers of substituted ethylbenzene derivatives benzenepropanenitrile, 64 and haloethylbenzenes. 65 The aliphatic CH stretch region is more useful in distinguishing the side-chain conformation, as the composition of the fundamental modes changes with respect to the coupling of the four internal CH stretch coordinates. It is clear from Figure 4 that the IR−UV spectra of Ag and Ggπ conformers exhibit significant variation in the CH stretch region.…”

Theoretical, Solid‐State, and Solution Quantification of the Hydrogen Bond‐Enhanced Halogen Bond

“…In contrast, the consideration of heavier halogens (that halogen bond: X=Cl, Br, I) has lagged. The few studies of heavy organohalogens as hydrogen bond acceptors have largely been theoretical, [9–11] with only a handful of experimental [12–18] and database [19, 20] studies reported. The importance of addressing this deficiency is underscored by the recent proliferation of halogen bonding materials, the ubiquity of the hydrogen bond, and a recent appreciation that hydrogen bonding can significantly influence halogen bonding (vide infra).…”

Conformer Specific Ultraviolet and Infrared Detection of Nicotine in the Vapor Phase

“…The R2PI setup used has been described previously. − The specifics relating to this study are as follows. (S)-Nicotine purchased from Sigma-Aldrich was used as received.…”