MICROWAVE SPECTROSCOPIC INVESTIGATIONS OF THE C--H⋯π\cdots\pi CONTAINING COMPLEXES CH2_2F2⋯_2\cdotsPROPYNE AND CH2_2ClF⋯\cdotsPROPYNE

Author Institution: Department of Chemistry, Eastern Illinois University, 600; Lincoln Ave., Charleston, IL 61920The spectra of the CH$_2$F$_2\cdots$propyne and CH$_2$ClF$\cdots$propyne complexes have been studied by chirped-pulse and resonant cavity Fourier-transform microwave spectroscopy and by {\em ab initio} calculations at the MP2/6-311++G(2d,2p) level. Both complexes contain C--H$\cdots\pi$ contacts, with the halogen atoms angled towards the methyl group end of the propyne. While CH$_2$F$_2\cdots$propyne has $C_s$ symmetry, CH$_2$ClF$\cdots$propyne has $C_1$ symmetry, with the fluorine and chlorine atoms straddling the propyne. \vspace{1em} Investigation of four single $^{13}$C and the DC$\equiv$CCH$_3$ isotopologues in CH$_2$F$_2\cdots$propyne has allowed a detailed structural determination, while only the $^{35}$Cl and $^{37}$Cl isotopologues have so far been assigned for CH$_2$ClF$\cdots$propyne. Experimental data will be compared with {\em ab initio} results and with the analogous acetylene complexes, both of which have $C_s$ symmetry structures, with double C--H$\cdots\pi$ interactions

Rotational Spectroscopic Studies of C–H···F Interactions in the Vinyl Fluoride···Difluoromethane Complex

Rotational spectra of the normal isotopic species and three ¹³C isotopologues of the 1:1 complex between vinyl fluoride (CH₂CHF) and difluoromethane (CH₂F₂) have been measured using 480 MHz bandwidth chirped-pulse Fourier-transform microwave spectroscopy in the 6.5–20 GHz region. A structure for this dimer has been determined by fitting the moments of inertia of all isotopologues and confirmed by calculation of Kraitchman single isotopic substitution coordinates. The structure is consistent with that determined by ab initio geometry optimization at the MP2/6-311++G­(2d,2p) level and has the difluoromethane subunit located on the CHF side of the vinyl fluoride subunit with three C–H···F contacts and with the hydrogen atoms of the CH₂F₂ straddling the vinyl fluoride symmetry plane

Characterization of Two Isomers of the Vinyl Fluoride···Carbon Dioxide Dimer by Rotational Spectroscopy

Rotational spectra of two different structural forms of the 1:1 weak complex between vinyl fluoride (C₂H₃F) and carbon dioxide were measured using 480 MHz bandwidth chirped-pulse and resonant cavity Fourier-transform microwave spectroscopy in the 5–17 GHz region. Both structures have the CO₂ molecule situated in the plane of the vinyl fluoride, such that the CO₂ is interacting either with a CHF side or with a HCCF edge of the vinyl fluoride subunit. Both observed structures are close to those predicted by <i>ab initio</i> geometry optimizations (corrected for basis set superposition error) at the MP2/6-311++G­(2d,2p) level. Dipole moment measurements and structural fits, including determinations of principal axis coordinates for all three carbon atoms, confirm the geometries of the assigned species

Alkynes as CH/π Acceptors: Microwave Spectra and Structures of the CH₂F₂···Propyne and CH₂ClF···Propyne Dimers

Rotational spectra of weakly bound complexes of chlorofluoromethane (CH₂ClF) and difluoromethane (CH₂F₂) with propyne (HCCCH₃) have been measured using chirped-pulse and resonant-cavity Fourier-transform microwave spectroscopy, adding to a relatively small body of high resolution spectroscopic data on propyne complexes. Both dimers contain CH/π contacts, as well as secondary contacts between one or both halogen atoms and the methyl group of propyne. A detailed structural determination for CH₂F₂···propyne has been made by study of the normal, one deuterated and four ¹³C substituted isotopologues, with the second lowest energy configuration predicted from <i>ab initio</i> calculations agreeing well with the observed structure. Experimental rotational constants for the most abundant isotopologue of CH₂F₂···propyne are <i>A</i>₀₀ = 5815.5858(15) MHz, <i>B</i>₀₀ = 1341.1191(5) MHz, <i>C</i>₀₀ = 1099.2040(4) MHz (uncorrected for internal rotation effects), and the dipole moment components, determined by Stark effect measurements, are μ_<i>a</i> = 1.568(2) D, μ_<i>b</i> = 0.587(2) D, and μ_tot = 1.674(3) D. For CH₂ClF···propyne, only ³⁵Cl and ³⁷Cl isotopologues have been assigned, providing rotational constants and chlorine atom coordinates consistent with the lowest energy structure from a series of <i>ab initio</i> predictions. Rotational constants for the ³⁵Cl isotopologue are <i>A</i> = 3423.639(7) MHz, <i>B</i> = 1253.7562(20) MHz, and <i>C</i> = 1200.4828(15) MHz and the diagonal and two off diagonal components of the quadrupole coupling tensor have also been determined