The complexes of halothane with benzene: the temperature dependent direction of the complexation shift of the aliphatic C–H stretching

Abstract

The formation of C-H...π bonded complexes of halothane with benzene(-d(6)) has been studied using infrared and Raman spectroscopy of solutions in liquid krypton, in supersonic jet expansions and in room temperature vapour phase. The formation of complexes with 1 ∶ 1 and 2 ∶ 1 stoichiometry was observed. The complexation enthalpy in liquid krypton for the 1 ∶ 1 complex was determined to be -9.8(2) kJ mol(-1) and the enthalpy for the addition of a second halothane molecule to the 1 ∶ 1 complex was determined at -7.0(3) kJ mol(-1). The stretching mode of the halothane C-H bond involved in the formation of the complex in the jets was observed to blue shift by 7.7(10) cm(-1). In contrast, for the solutions of liquid krypton and the room temperature measurements a small red shift was observed. Supported by ab initio calculations and Monte Carlo simulations, this shift was explained by the differences in thermal populations of the van der Waals vibrations of the complex in the different experiments.

Infrared and Raman Measurements of Halogen Bonding in Cryogenic Solutions

“…The blue shifts of + 2.6 cm À1 for the CF 3 Br complex and + 4.6 cm À1 for CF 3 I are in line with ab initio complexation shifts and agree favorably with data reported in earlier studies showing that the C-H out of plane bending mode in benzene is largely perturbed by C-H proton donors such as halothane, CF 3 CBrClH [67], and sevoflurane, (CF 3 ) 2 CHOCH 2 F [64], and other Lewis acids such as hexafluorobenzene, C 6 F 6 [136].…”

“…Solutions in LRGs have also proven to be an ideal medium to study the spectroscopic and thermodynamical properties of complexes held together by weak red-or blue-shifting C-H. . .X hydrogen bonds, typical Lewis acids studied so far [31,64,67, being CHF 3 , CHF 2 Cl, CHFCl 2 , CHCl 3 , CF 2 CFH, C 2 H 2 , and CF 3 CCH.…”

Exploring the C-X…π Halogen Bonding Motif: An Infrared and Raman Study of the Complexes of CF3X (X = Cl, Br and I) with the Aromatic Model Compounds Benzene and Toluene

“…Analysis of the data in the different panels of Figure 4 reveals that for both CF 3 Br and CF 3 I a new band appears on the high frequency side of the 674.8 cm for CF 3 I are in line with the ab initio complexation shifts, presented in Table 4, and agree favorably with data reported in earlier studies showing that the C-H out of plane bending mode ν 4 (A 2u ) in benzene is largely perturbed by C-H proton donors such as halothane, CF 3 CBrClH [20], and sevoflurane, (CF 3 ) 2 CHOCH 2 F [21], and other Lewis acids such as hexafluorobenzene, C 6 F 6 [24].…”

“…These trends are in line with earlier observations showing that also for other complexes involving the aromatic model compounds including, amongst others, the complexes of benzene with the anesthetics halothane [20] and sevoflurane [21], MP2/aug-cc-pVTZ (-PP) ab initio calculations tend to seriously overestimate the complexation energies and the corresponding complexation enthalpies. The overestimation, most likely, is due to imperfections related to the MP2 second order perturbation approach used.…”

“…The vibrational spectra of the trifluorohalomethanes CF 3 Cl, CF 3 Br and CF 3 I and of benzene dissolved in liquid rare gases have been studied in detail before [10,13,20,21] and are not commented here. The observed frequencies for toluene dissolved in LKr and their assignments, based on literature data for the vapor and liquid phases [19] and on the harmonic vibrational frequencies derived at the MP2/aug-cc-pVDZ and MP2/aug-cc-pVTZ levels, are summarized in Table S7.…”