Intermolecular Interactions between Halothane and Dimethyl Ether: A Cryosolution Infrared and Ab Initio Study

Abstract

The complex of halothane (CHClBrCF(3)) and dimethyl ether has been investigated experimentally in solutions of liquid krypton using infrared spectroscopy and theoretically using ab initio calculations at the MP2/6-311++G(d,p) level. The formation of a 1:1 complex was experimentally detected. The most stable ab initio geometry found is the one in which the C--H bond of halothane interacts with the oxygen atom of dimethyl ether. The complexes in which the chlorine or the bromine atom of halothane interacts with the oxygen atom of the ether were found to be local energy minima and were less stable by 14.5 and 9.3 kJ mol(-1), respectively, than the global minimum. The formation of a single complex species was observed in the infrared spectra; the standard complexation enthalpy of this complex was determined to be -12.3(8) kJ mol(-1). Analysis of the observed complexation shifts supports the identification of the complex as the hydrogen-bonded species. The C--H stretching vibration of halothane was found to show a redshift upon complexation of 19(2) cm(-1). The infrared intensity ratios epsilon(complex)/epsilon(monomer) for the fundamental and its first overtone were measured to be 6.5(1) and 0.31(1). The frequency shift was analyzed using Morokuma-type analysis, and the infrared intensity ratios were rationalized using a model including the mechanical and electric anharmonicity of the C--H stretching fundamental.

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

“…The interferograms were averaged over 500 scans, Blackmann-Harris three-term apodized and Fourier transformed to yield spectra with a resolution of 0.5 cm . The experimental set-up to study the solutions in liquid noble gases has been described in detail before [31,32]. A liquid cell equipped with wedged Si windows and with a path length of 1 cm was used to record the spectra.…”

CX⋅⋅⋅O Halogen Bonding: Interactions of Trifluoromethyl Halides with Dimethyl Ether

“…[41,42] First, a BSSE-corrected value for the energy of a complex is calculated by completely relaxing the structure at the MP2/6-311 + + GA C H T U N G T R E N N U N G (d,p) level, and the complexation energy is obtained by subtracting the corresponding monomer energies. The obtained structure is then used in single-point calculations to obtain BSSE-corrected complexation energies at the MP2/aug-cc-pVXZ (with X = D, T and Q) level.…”

“…The plots are roughly linear, with correlation coefficients for the linear regression lines of 0.81, 0.58 and 0.79 for chloride, bromide and iodide. The presence of a clear correlation is taken, as before, [42] to lend support to the proposed structure of the complexes.…”

“…This study is a first contribution to fill this gap, by studying the infrared and Raman spectra of complexes of CF 3 X (X= Cl, Br, I) with dimethyl ether, in liquid rare gases, a technique that allows not only the straightforward detection of complex formation, but also allows the determination of complexation enthalpies as a measure of their stabilities. [41,42] The interest of the halogen bonding community in the Lewis bases proposed is reflected by a recent theoretical study into the origins of halogen bonding, [39] where it was shown that in the series CF 3 X, the surface electrostatic potential of the X-atom shows a positive region on the outermost portion of the surface, around its intersection with the CÀX axis, the socalled s-hole. The size and "depth" of the hole increase from X = Cl to X = I.…”

“…To the best of our knowledge, the present results on DME·CF 3 Cl are the first experimental confirmation of such a blue-shift. In principle, and in analogy to what was done for the blue-shifting hydrogen bonds, [42,54] an analysis of the possible origins of that shift in terms of the Buckingham model [55] could be made. However, the observed shift upon complexation is a mere +2.0 cm…”