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The Microwave Spectrum and Molecular Structure of (Z)-1-Chloro-2Fluoroethylene-Acetylene: Demonstrating the Importance of the Balance Between Steric and Electrostatic Interactions in Heterodimer Formation Helen O. Leung, Mark D. Marshall, and Nazir D. Khan J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b05101 • Publication Date (Web): 10 Jul 2017 Downloaded from http://pubs.acs.org on July 17, 2017

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The Journal of Physical Chemistry

The Microwave Spectrum and Molecular Structure of (Z)-1-Chloro-2Fluoroethylene− −Acetylene: Demonstrating the Importance of the Balance Between Steric and Electrostatic Interactions in Heterodimer Formation Helen O. Leung,* Mark D. Marshall,* and Nazir D. Khan Department of Chemistry, Amherst College, P.O. Box 5000, Amherst, MA 01002-5000

Address for correspondence: Prof. Mark D. Marshall Department of Chemistry Amherst College P.O. Box 5000 Amherst, MA 01002-5000 Telephone: (413) 542-2006 Fax: (413) 542-2735 E-mail: [email protected] *

Corresponding authors. Fax: +1-413-542-2735; e-mail addresses: [email protected] (H.O. Leung), [email protected] (M.D. Marshall). The authors declare no competing financial interest. -1ACS Paragon Plus Environment


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Abstract The structure of the gas-phase heterodimer formed between (Z)-1-chloro-2fluoroethylene and acetylene is determined via Fourier transform microwave spectroscopy from 5.5 to 20.8 GHz. In the first instance where in the presence of both a fluorine atom and a chlorine atom on the haloethylene the protic acid binds to the chlorine atom, the acetylene adopts a configuration similar to that in the analogous complex with vinyl chloride. Positioned in a manner to interact favorably with both the chlorine atom and the hydrogen atom geminal to it, the acetylene molecule is able to maximize the overall electrostatic stabilization even though other regions of the haloethylene offer individual sites of greater positive or negative electrostatic potential. Detailed comparison with the vinyl chloride-acetylene complex suggests that the presence of the fluorine atom weakens the hydrogen bond, but strengthens the interaction between the geminal hydrogen atom and the triple bond.

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1.


Introduction To understand the differences in the manners in which fluorine and chlorine moderate intermolecular interactions, we have been examining molecular complexes between vinyl chloride and protic acids and comparing them to their vinyl fluoride counterparts. The acids of interest are HF, HCl, and HCCH and the structures of their vinyl fluoride complexes have been reported by the Legon group.1-3 The binding mode for these effectively planar complexes are identical: the acid forms a hydrogen bond with fluorine in vinyl fluoride, and a bend in the bond allows the nucleophilic portion of the acid to forge a secondary interaction with the hydrogen located cis to fluorine. We term this configuration “top” binding. On the other hand, the complexes of vinyl chloride do not share a common motif. Two of them are planar; but while HF binds across the double bond of vinyl chloride, interacting with the F and H pair4 much like its vinyl fluoride counterpart (top binding), HCCH interacts with the F and H pair bonded to the same carbon atom (“side binding”).5

The complex vinyl chloride-HCl adopts a nonplanar

configuration and exhibits tunneling motion.6-7 The structures of these planar complexes can be explained by a consideration of electrostatic and steric effects. (Work on the nonplanar vinyl chloride-HCl is on-going.) Mapping the electrostatic potential of vinyl fluoride onto its electron density surface, as shown in Fig. 1a, shows that the H atom geminal to the F atom is much more electropositive than that located in the cis position; thus, from a purely electrostatics consideration, a stronger secondary interaction would result when it is formed by the acid and the geminal H atom. To achieve such an interaction, however, the hydrogen bond must bend by a much greater extent than one where the secondary interaction is formed with the H atom in the cis position. The fact that it is not



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observed indicates that the more favorable electrostatic interaction in the secondary bond is not sufficient to compensate for a sterically unstable side binding configuration. This conclusion is supported by our work on trans-1,2-difluoroethylene-HF.8 Because of the symmetry in trans1,2-difluoroethylene, both top and side binding modes are electrostatically equivalent. The observed top binding mode thus indicates that it is sterically more favorable. Nevertheless, side-binding configurations are observed in another class of fluoroethyleneprotic acid complexes: those involving 1,1,2-trifluoroethylene. Even though 1,1,2trifluoroethylene offers the possibility for binding across the double bond, all three acids – HF,9 HCl,10 and HCCH11 – interact with the F and H atoms connected to C-2. Because there is only one possible H atom for the secondary interaction, the observed structures of these complexes suggest that the primary hydrogen bond formed with the F atom connected to C-2 must be stronger than that formed with the F atom located cis to the H atom. Indeed, the mapped electrostatic potential of 1,1,2-trifluoroethylene onto its total electron density surface (Fig. 1b) shows that the F atom forming the hydrogen bond is the most negative of all the F atoms. For these complexes, the electrostatically more stable primary hydrogen bond can overcome the unfavorable steric factors in the side-binding configuration. In addition to decreasing nucleophilicity, the substitution of an F atom by a Cl atom also changes the electron density distribution about the halogen atom in vinyl halide. While the most negative potential points away from the F atom along the C–F bond in vinyl fluoride, it is concentrated on a band centered about the Cl atom more or less perpendicular to the C–Cl bond in vinyl chloride.5 As a result, the hydrogen bond can form a smaller angle with a C–Cl bond than with a C–F bond. Unlike vinyl fluoride complexes, both top and side binding modes are observed for vinyl chloride complexes, as we mentioned earlier. Once again, as in vinyl


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fluoride, the H atom geminal to the halogen atom in vinyl chloride is more electropositive than the one in the cis position.5 The acid HF binds to vinyl chloride in the top binding configuration, indicating that, as in the case of vinyl fluoride-HF, the cost for a sterically strained side binding configuration is too high to be compensated by an electrostatically more favorable secondary interaction. On the other hand, HCCH is a weaker acid and the hydrogen bond can therefore be distorted more easily, allowing the acid to form the secondary interaction with the more electropositive H atom geminal to Cl. When both F and Cl atoms are present in the same ethylene subunit, we can study the interplay among the different electrostatics and steric factors offered by the halogen atoms. In the case of 1-chloro-1-fluoroethylene-HCCH,12 the ethylene subunit offers two possible top binding modes, each involving a halogen and a hydrogen atom located cis to each other. The observed complex is fluorine bound; the preference of fluorine over chlorine is likely a result of the greater electronegativity of fluorine. Interestingly, the structural parameters of this complex are the same to within experimental uncertainties as those of its 1,1-difluoroethylene counterpart.13 Thus, replacement of a F atom in 1,1-difluoroethylene by Cl has little effect on the nature of intermolecular interactions involving the F, H pair located cis to each other. This is somewhat surprising as one might expect Cl, a less electronegative atom, would affect the nucleophiciity of the F atom to a lesser extent than another F atom, and therefore, would make the primary bond stronger and shorter. The fact that this is not observed is perhaps a consequence of Cl withdrawing electrons in the ethylene subunit through resonance while a second F atom does so through induction, an issue that we are investigating by furthering our work on chlorofluoroethylene complexes.



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We report here our work on (Z)-1-chloro-2-fluoroethylene-HCCH. This time, F and Cl are located cis to each other, leaving only two side binding modes possible for HCCH. Since F is more electronegative than Cl as can be seen in Fig. 1c, the H atom geminal to F is more electropositive. Consequently, a side binding configuration involving this F, H pair should be more electrostatically favorable. On the other hand, the sets of atoms at the two ends of the double bond offer different steric factors. Indeed, as we show below, the favorable sterics offered by the Cl, H pair outweighs the electrostatic advantage of the F, H pair for HCCH. 2.

Ab Initio Calculations To aid our search for the spectrum of (Z)-1-chloro-2-fluoroethylene-HCCH, we carried out ab initio calculations at the MP2/6-311++G(2d,2p) level with GAUSSIAN 0914 to locate the minima on the interaction potential surface of the two subunits. The structures of the subunits are fixed to the average structures of the free monomers.15-16 We located four minima; their relative energies, without and with basis set superposition error (BSSE) correction, and rotational constants are listed in Table 1 and the corresponding structures are shown in Fig. 2. (The

principal coordinates of the atoms in each structure are available as supplementary material.) The global minimum corresponds to a side binding planar configuration where the hydrogen bond is formed between acetylene and Cl in (Z)-1-chloro-2-fluoroethylene [Structure (c) in Fig. 2]. When BSSE correction is not taken into account, the next higher energy structure is a nonplanar structure, where three interactions are apparent [Structure (b)]: HCCH forms a hydrogen bond to each halogen atom in the ethylene subunit with dispersion interactions between the electron densities of the acetylene triple bond and the ethylene double bond (the distance between the centers of these bonds is 3.815 Å). The H...Cl hydrogen bond is 0.286 Å longer than the H...F bond, which is similar to the 0.28 Å difference between the van der Waals


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radii of the Cl and F.17 When BSSE correction is included, Structure (b) has the highest energy of the four structures. Structures (d) and (a) have similar energies, with the former 8 cm−1 lower in energy (with or without BSSE correction). Structure (d) is another nonplanar structure, with the ethylene subunit bisecting the acetylene, which interacts with the two H atoms of the ethylene and is normal to the ethylene plane. It is interesting to note that the interaction length with the H atom bonded to C-2 is 0.052 Å shorter than that bonded to C-1, suggesting that the former H atom is more electropositive, likely because of its proximity to the electronegative F atom. Because Structure (c) is significantly lower in energy than the other structures, we expect that it is the only one observable under our experimental conditions. The calculated dipole moment components are quite large: µa = 1.38 D, and µb = 1.94 D, and by virtue of the planarity of the structure, µc = 0. 3.

Experiment Both a broadband, chirped pulse18-20 and a narrow band, Balle-Flygare,19, 21 Fourier transform microwave spectrometer are employed for this work. These spectrometers have been described previously and only specific experimental details are reported here. The complex is formed by expanding a gas mixture containing 1% each of (Z)-1-chloro-2-fluoroethylene (SynQuest Laboratories, Achala,FL, lot Q115-85) and an appropriate isotopologue of HCCH in Ar, with a backing pressure of 1 – 2 atm. The Balle-Flygare spectrometer uses one pulsed valve with a 0.8 mm diameter nozzle, while the chirped pulse spectrometer uses two. The rotational spectrum of the complex (formed with the most abundant isotopologue of HCCH) is first collected in the broadband spectrometer in 3.5 to 4.0 GHz segments from 5.6 to 18.1 GHz. The chirped microwave polarization pulse duration is 4 µs with 20 – 25 W of power, and the resulting



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FID is digitized at 50 Gs s–1 for 10 µs beginning 0.5 µs after the end of the excitation pulse. 10 FIDs are collected during each 700 µs opening of the two pulsed valves which typically operate at 4 Hz, although this is reduced to 0.8 Hz for overnight operation. 426,000 to 564,000 FIDs are averaged for each segment, and as described previously,19 the average is Fourier transformed to give a frequency domain spectrum with a resolution element of 23.84 kHz and typical line widths (FWHM) of 225 kHz. Using Kisiel’s AABS package,22 transitions for (Z)-CHFCH35Cl– HCCH and (Z)-CHFCH37Cl–HCCH are identified and fit (as described more fully below) to give spectroscopic constants, which are used to predict other transitions. We then measure the transitions using the high resolution Balle-Flygare spectrometer in the 5.5 – 20.8 GHz region. In addition to the spectra for (Z)-CHFCH35Cl–HCCH and (Z)-CHFCH37Cl–HCCH, we obtain the spectrum for (Z)-13CHFCH35Cl–HCCH in natural abundance. We also use H13CCH (Icon Isotopes) and H13C13CH (Cambridge Isotopes) to collect the spectra for (Z)-CHFCH35Cl– H13CCH, (Z)-CHFCH35Cl–HC13CH, (Z)-CHFCH35Cl–H13C13CH, (Z)-CHFCH37Cl–H13CCH, and (Z)-CHFCH37Cl–H13C13CH. (Because of the limited H13CCH sample, the spectrum for (Z)CHFCH37Cl–HC13CH was not obtained.) The background-corrected time domain signals for the narrowband spectra are digitized for 1024 data points and zero-filled to a 2048-point record length before Fourier transformation to give a frequency domain signal with a resolution element of 4.8 kHz. 4.

Results

A.

Spectral Analysis Although the chirped pulse spectrum is congested with the presence of transitions arising

from the isotopologues of (Z)-1-chloro-2-fluoroethylene and of their argon complexes, we are readily able to assign transitions to (Z)-CHFCH35Cl–HCCH and (Z)-CHFCH37Cl–HCCH. A


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portion of the spectrum is shown in Fig. 3a and 3b, with 6 rotational transitions indicated. Each transition is split by the quadrupolar chlorine nucleus in (Z)-1-chloro-2-fluoroethylene. The hyperfine components in the b-type transitions are well separated but those in a-type transitions are not. In fact, for the 616 – 515 transition in the chirped pulse spectrum, only one line is observed, which, when examined using the Balle-Flygare spectrometer, is resolved into 4 Doppler-doubled hyperfine components spread over a 330 kHz range as shown in Fig 3c for the most abundant isotopologue. Using the higher resolution instrument, we observe 78 – 156 rotational transitions for the four isotopologues of (Z)-1-chloro-2-fluoroethylene-HCCH that contain the most abundant HCCH and the H13C13CH subunits, and 28 – 32 transitions for the three isotopologues containing H13CCH. Because 13CHFCH35Cl–HCCH was studied in natural abundance, we are able to measure only 11 transitions for this species and none for CHF13CH35Cl–HCCH, for which the substitution is additionally very close to the center of mass for the complex. All of the observed transitions are a- and b-type, and no c-type transitions are observed, which is consistent with a planar geometry for the complex. Large J and Ka ranges are sampled, especially in the most abundant isotopologue, but for the rest of the species, the J values range from 0 or 1 to at least 7, and the Ka values from 0 to at least 2. The spectrum of each isotopologue is analyzed using the Watson A-reduced Hamiltonian23 with the inclusion of nuclear quadrupole coupling interactions due to the chlorine nucleus. Using Pickett’s nonlinear SPFIT program24 for each species, we fit 3 rotational constants, 4 – 5 quartic centrifugal distortion constants, and for the most abundant species and its 37Cl isotopologue, 2 to 3 sextic centrifugal constants. Additionally, we determine the diagonal components of the chlorine nuclear quadrupole coupling tensor. These constants are tabulated in Tables 2 and 3. We have also included tables of observed and calculated



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transition frequencies with assignments for all isotopologues studied as Supporting Information. The rms deviation of each fit is less than 2 kHz, smaller than the resolution element of 4.8 kHz. While the S-reduced Watson Hamiltonian provided fits with a very small value for d2 (−0.0314 kHz) compared to the somewhat larger 5.26 kHz for δK in the A reduction, the qualities of the fits are essentially identical, and the precisions to which these constants are determined is likewise comparable. B.

Structure Determination (Z)-1-chloro-2-fluoroethylene-HCCH is a near prolate asymmetric top, with an

asymmetry parameter value between −0.913 and −0.901 for the isotopologues. The slightly negative inertial defect (between −0.209 and −0.185 u Å2 for the isotopologues) is characteristic of a planar complex where out-of-plane vibrational contribution is dominant. The experimental rotational constants for the most abundant species agree with those for the theoretical equilibrium structure of the lowest energy isomer [Structure (c)], differing by no more than 4%, confirming that the average structure of the complex has a side binding configuration, with HCCH interacting with Cl and H bonded to C-1. Using the four isotopologues that contain a single substitution in (Z)-CHFCH35Cl–HCCH (the 37Cl containing species and three species singly substituted with 13C), we calculate the absolute values of the Kraitchman coordinates25 for C-2 and Cl in the ethylene subunit, and the C atoms in HCCH. These are listed in Table 4 together with their Costain error.26 To more precisely determine the geometric parameters, we fit them to the moments of inertia of the isotopologues. Because the complex is planar, only two of three moments of inertia are independent. We determine the structure by fitting the distance between the two subunits and their angular orientations to Ia and Ic of each of the eight isotopologues using Schwendeman’s

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STRFTQ program.27 The rms deviation of the fit is 0.035 u Å2. Here we give the chemically relevant parameters: the hydrogen bond between HCCH and Cl forms an angle of 87.843(97)o with the C–Cl bond; it has a length of 3.0690(89) Å and bends by 62.44(43)o to allow the H geminal to Cl in the ethylene subunit to interact with the acetylenic bond. This interaction has a length of 2.7815(8) Å (Fig. 4). The coordinates for the C-2 and Cl atoms in the ethylene subunit and the C atoms in the HCCH subunit are listed in Table 4. They agree very well with the Kraitchman coordinates. C.

Nuclear Quadrupole Coupling Constants Both the (Z)-1-chloro-2-fluoroethylene monomer and its HCCH complex are planar and

therefore, their c axes point in the same direction. A comparison of the values of χ cc due to chlorine nuclear quadrupole coupling interactions [33.3403(82) MHz for 35Cl in the monomer19 and 32.82630(59) MHz for the dimer with similar agreement seen for 37Cl] shows that the value in the dimer is 1.5% smaller than that of the monomer. This difference may indicate that the electric field gradient at the Cl nucleus is slightly perturbed, or more likely, it demonstrates that the zero point motion of the (Z)-1-chloro-2-fluoroethylene subunit in the complex is different from that on its own as a the monomer. Although we were unable to determine experimentally the values of χ ab for any of the isotopologues of (Z)-1-chloro-2-fluoroethylene-HCCH, they can be estimated using the quadrupole coupling tensor of of the (Z)-1-chloro-2-fluoroethylene monomer. We will consider the most abundant isotopologues of the monomer and the dimer here. When the matrix that rotates the inertial tensor of the monomer to that of the dimer is applied to the nuclear quadrupole coupling tensor of the monomer, we can obtain the tensor of the dimer assuming that the two species exhibit the same zero point vibrational motion. The values of χ aa and χ bb for - 11 ACS Paragon Plus Environment


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the dimer thus determined are 40.6561 and −73.9964 MHz, respectively, differing from the experimental values by only 2%. The value of χ ab is −2.2281 MHz, with sign as appropriate for the atomic arrangement of the complex and the directionality of the principal inertial axes shown in Fig. 4. The small magnitude of this value indicates that the principal electric field gradient axes in the molecular plane of the dimer are almost parallel to the inertial axes. As we have observed in other chloroethylene complexes,28-29 one of the principal electric field gradient axes is more or less along the C–Cl bond and we expect this to be so here, too. Indeed, using structural parameters given in the last section, the C–Cl bond makes an angle of only 0.68o with the b inertial axis. 5.

Discussion The experimental structure of (Z)-1-chloro-2-fluoroethylene-HCCH agrees excellently

with the theoretical global minimum structure [Structure (c)]. The experimentally observed and theoretically predicted values of the CCl...H angle and of the C–Cl bond length are identical to within experimental uncertainties. The hydrogen bond in the experimental structure bends by 62.44(43)o, which is 3.5o smaller than that in the equilibrium structure. As a result, the secondary interaction length between H in the ethylene subunit and the acetylenic bond in the experimental structure is longer than the equilibrium structure by 0.10 Å. It is interesting to note that this so-called secondary interaction is shorter than the hydrogen bond by 0.29 Å in the experimental structure. A comparison between the structure of (Z)-1-chloro-2-fluoroethylene-HCCH and its vinyl chloride counterpart5 shows that the values of the CCl...H angle are very similar, differing by only 0.9o. This ~88o angle is consistent with the location of the most negative potential at the Cl atom. The hydrogen bond of the (Z)-1-chloro-2-fluoroethylene complex is longer by 0.06 Å,


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suggesting that the presence of a F atom in the ethylene subunit decreases the nucleophilicity of the Cl atom, making the hydrogen bond weaker, and therefore, it bends more (by 3.9o) from linearity. The secondary interaction between the geminal H and the acetylenic bond in the (Z)-1chloro-2-fluoroethylene is shorter by 0.16 Å than in its vinyl chloride counterpart, indicating that it plays a more significant role in stabilizing the complex. This is the first complex observed where in the presence of both F and Cl in the ethylene subunit, the acid prefers to bind to the Cl atom. We can gain some insight into this mode of bonding by considering the ab initio results (Fig. 2). We do not observe the higher energy side binding configuration involving the F, H pair connected to C-2 [Structure (a)]. This configuration is much higher in energy than Structure (c), which corresponds to the experimental structure. A comparison between these two side binding structures shows that the Cl...H hydrogen bond in Structure (c) is 3.071 Å, which is 0.50 Å longer than the F...H hydrogen bond in Structure (a). This is 1.8 times the difference between the van der Waals radii of Cl and F, indicating that the hydrogen bond in Structure (c) is weaker. On the other hand, the secondary interaction between the acetylenic bond and H atom in Structure (c) is 2.683 Å, which is 0.20 Å shorter than its counterpart in Structure (a). To achieve this secondary interaction, the hydrogen bond in Structure (c) has to bend by 65.9o from linearity, somewhat greater than the 61.2o in Structure (a). The greater distortion in Structure (c) is likely made possible because it has a weaker hydrogen bond. Judging from the differences between bond lengths, it appears that although the secondary bond in Structure (c) is stronger than that in Structure (a), it is not likely to be strong enough to make up for the significantly weaker Cl...H interaction compared to the F...H interaction. The fact that Structure (c) is significantly lower in energy therefore suggests that the CCl...H angle in Structure (c) is closer to its ideal value than is the CF...H angle in



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Structure (a). Thus, even though it is a smaller angle, there is less strain in the CCl...H angle in Structure (c) than in the CF...H angle in Structure (a). When we map the electrostatic potential of (Z)-1-chloro-2-fluoroethylene onto its electron density surface (Fig. 1c), the most negative portion of the molecule is found to be between the two halogen atoms in the ethylene. Indeed, an H atom of HCCH in Structure (b) is attracted to this part of the molecule. The fact that it has a much higher energy than Structure (c) suggests once again, the most electrostatically stable configuration cannot compete with the loss of a secondary interaction and possibly the steric constraints associated with achieving the bifurcated hydrogen bonds.

6.

Conclusions As the first chlorofluoroethylene-protic acid complex observed for which the lowest

energy structure has the acid bonding to the less electronegative Cl atom, the structure of the gasphase heterodimer formed between (Z)-1-chloro-2-fluoroethylene and acetylene demonstrates quite nicely the role steric interactions plays in determining the overall best compromise among competing electrostatic interactions. Undoubtedly, as the weakest gas-phase acid among HF, HCl, and HCCH, the electrostatic interaction between the HCCH hydrogen bond donor and its acceptor is most subject to the effects of the other interactions responsible for the stability of the complex. A comparison with the structure of vinyl chloride-acetylene,5 where the side-binding arrangement was seen to provide the “best fit,” shows qualitatively similar geometrical parameters for the two species. Upon closer examination, a longer hydrogen bond and a greater deviation from linearity suggest that the hydrogen bond in (Z)-1-chloro-2-fluoroethyleneacetylene is weaker than that of its vinyl chloride counterpart. Additionally, a shorter distance between the H atom geminal to Cl and the center of the C≡C triple bond indicates that this - 14 ACS Paragon Plus Environment

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interaction plays a more significant role in stabilizing (Z)-1-chloro-2-fluoroethylene-acetylene than it does in vinyl chloride-acetylene. Taken together, these two interactions provide stronger bonding than would the single interactions between the two most complementary electrostatic regions of each molecule. One of two such possibilities is represented in Structure (b) of Fig. 2, where the electropositive hydrogen atom of the acetylene is positioned close to the most negative region of the haloethylene (Fig. 1c) and the second in Structure (d) of Fig. 2, where the electron-rich triple bond of acetylene interacts with the two hydrogen atoms of (Z)-1-chloro-2-fluoroethylene at its most positive site. Finally, with the top-binding arrangement of vinyl fluoride-acetylene3 or 1,1-difluoroethyleneacetylene13 blocked by the Cl atom, the two interactions afforded by the fluorine-bound Structure (a) of Fig. 2 cannot compensate for the better fit of the observed structure. Acknowledgements This material is based on work supported by the National Science Foundation under Grant No. CHE-1465014. Supporting Information Available: Tables of observed and calculated transition frequencies for all isotopologues of (Z)-1-chloro-2-fluoroethylene-acetylene that are reported in this study are available as supplementary material, as are the atomic coordinates for the structures shown in Fig. 2 and the complete citation for Gaussian 09. This material is available free of charge via the Internet at http://pubs.acs.org



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References 1.

Cole, G. C.; Legon, A. C. A Characterisation of the Complex Vinyl Fluoride•••Hydrogen Fluoride by Rotational Spectroscopy and Ab Initio Calculations. Chem. Phys. Lett. 2004, 400, 419-424.

2.

Kisiel, Z.; Fowler, P. W.; Legon, A. C. Rotational Spectrum, Structure, and Chlorine Nuclear Quadrupole Tensor of the Vinyl Fluoride-Hydrogen Chloride Dimer. J. Chem. Phys. 1990, 93, 3054-3062.

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Cole, G. C.; Legon, A. C. Non-Linearity of Weak B ••• H-C Hydrogen Bonds: An Investigation of a Complex of Vinyl Fluoride and Ethyne by Rotational Spectroscopy. Chem. Phys. Lett. 2003, 369, 31-40.

4.

Leung, H. O.; Marshall, M. D. The Effect of Acid Identity on the Geometry of Intermolecular Complexes: The Microwave Spectrum and Molecular Structure of Vinyl Chloride-HF. J. Phys. Chem. A 2014, 118, 9783-9790.

5.

Leung, H. O.; Marshall, M. D.; Feng, F. The Microwave Spectrum and Molecular Structure of Vinyl Chloride-Acetylene, a Side-Binding Complex. J. Phys. Chem. A 2013, 117, 13419-13428.

6.

Messinger, J. P.; Leung, H. O.; Marshall, M. D. The Effect of Protic Acid Identity on the Structures of Complexes with Vinyl Chloride: Fourier Transform Microwave Spectroscopy and Molecular Structure of the Vinyl Chloride-Hydrogen Chloride Complex. The 69th International Symposium on Molecular Spectroscopy, Talk TE07, Urbana-Champaign, IL, 2014.


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7.

Leung, H. O.; Marshall, M. D.; Messinger, J. P. Chlorine Nuclear Quadrupole Hyperfine Structure in the Vinyl Chloride-Hydrogen Chloride Complex. The 70th International Symposium on Molecular Spectroscopy, Talk WJ06, Urbana-Champaign, IL, 2015.

8.

Leung, H. O.; Marshall, M. D.; Amberger, B. K. Fourier Transform Microwave Spectroscopy and Molecular Structure of the Trans-1,2-Difluoroethylene–Hydrogen Fluoride Complex. J. Chem. Phys. 2009, 131, 204302.

9.

Leung, H. O.; Marshall, M. D. Rotational Spectroscopy and Molecular Structure of 1,1,2Trifluoroethylene and the 1,1,2-Trifluoroethylene-Hydrogen Fluoride Complex. J. Chem. Phys. 2007, 126, 114310.

10.

Leung, H. O.; Marshall, M. D.; Ray, M. R.; Kang, J. T. Rotational Spectroscopy and Molecular Structure of the 1,1,2-Trifluoroethylene-Hydrogen Chloride Complex. J. Phys. Chem. A 2010, 114, 10975-10980.

11.

Leung, H. O.; Marshall, M. D.; Cashion, W. T.; Chen, V. L. Rotational Spectroscopy and Molecular Structure of the 1,1,2-Trifluoroethylene-Acetylene Complex. J. Chem. Phys. 2008, 128, 064315.

12.

Leung, H. O.; Marshall, M. D.; Grimes, D. D. Rotational Spectroscopy and Molecular Structure of the 1-Chloro-1-Fluoroethylene-Acetylene Complex. J. Chem. Phys. 2011, 134, 034303.

13.

Leung, H. O.; Marshall, M. D. Rotational Spectroscopy and Molecular Structure of the 1,1-Difluoroethylene-Acetylene Complex. J. Chem. Phys. 2006, 125, 154301.

14.

Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Revision B.01; Gaussian, Inc.: Wallingford, CT, 2009.



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Puzzarini, C.; Cazzoli, G.; Gambi, A.; Gauss, J. Rotational Spectra of 1-Chloro-2Fluoroethylene. II. Equilibrium Structures of the Cis and Trans Isomer. J. Chem. Phys. 2006, 125, 054307.

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Herman, M.; Campargue, A.; El Idrissi, M. I.; Vander Auwera, J. Vibrational Spectroscopic Database on Acetylene X1Σ+g. J. Phys. Chem. Ref. Data. 2003, 32, 9211360.

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Bondi, A. Van Der Waals Volumes and Radii. J. Phys. Chem. 1964, 68, 441-451.

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Marshall, M. D.; Leung, H. O.; Scheetz, B. Q.; Thaler, J. E.; Muenter, J. S. A Chirped Pulse Fourier Transform Microwave Study of the Refrigerant Alternative 2,3,3,3Tetrafluoropropene. J. Mol. Spectrosc. 2011, 266, 37-42.

19.

Marshall, M. D.; Leung, H. O.; Calvert, C. E. Molecular Structure of the Argon-(Z)-1Chloro-2-Fluoroethylene Complex from Chirped-Pulse and Narrow-Band Fourier Transform Microwave Spectroscopy. J. Mol. Spectrosc. 2012, 280, 97-103.

20.

Leung, H. O.; Marshall, M. D.; Messinger, J. P.; Knowlton, G. S.; Sundheim, K. M.; Cheung-Lau, J. C. The Microwave Spectra and Molecular Structures of 2-Chloro-1,1Difluoroethylene and Its Complex with the Argon Atom. J. Mol. Spectrosc. 2014, 305, 25-33.

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Leung, H. O.; Gangwani, D.; Grabow, J. U. Nuclear Quadrupole Hyperfine Structure in the Microwave Spectrum of Ar-N2O. J. Mol. Spectrosc. 1997, 184, 106-112.

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Kisiel, Z.; Pszczólkowski, L.; Medvedev, I. R.; Winnewisser, M.; deLucia, F. C.; Herbst, E. Rotational Spectrum of Trans–Trans Diethyl Ether in the Ground and Three Excited Vibrational States. J. Mol. Spectrosc. 2005, 233, 231-243.


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Watson, J. K. G. In Aspects of Quartic and Sextic Centrifugal Effects on Rotational Energy Levels; Durig, J. R. Ed.; Elsevier Scientific Publishing: Amsterdam, 1977; pp 189.

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Pickett, H. M. The Fitting and Prediction of Vibration-Rotation Spectra with Spin Interactions. J. Mol. Spectrosc. 1991, 148, 371-377.

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Kraitchman, J. Determination of Molecular Structure from Microwave Spectroscopic Data. Am. J. Phys. 1953, 21, 17-24.

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Costain, C. C. Determination of Molecular Structures from Ground State Rotational Constants. J. Chem. Phys. 1958, 29, 864-874.

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Schwendeman, R. H. In Critical Evaluation of Chemical and Physical Structural Information; Lide, D. R.; Paul, M. A. Eds.; National Academy of Science: Washington, DC, 1974.

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Leung, H. O.; Marshall, M. D.; Lee, A. J. The Microwave Spectrum and Molecular Structure of (E)-1-Chloro-2-Fluoroethylene−HF: Revealing the Balance Among Electrostatics, Sterics, and Resonance in Intermolecular Interactions. J. Phys. Chem. A 2016, 120, 7935-7946.

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Leung, H. O.; Marshall, M. D. The Microwave Spectrum and Molecular Structure of (E)1-Chloro-2-Fluoroethlyene-Hydrogen Chloride. J. Phys. Chem. A 2016, 120, 7955-7963.



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Table 1. The relative energies, without and with BSSE correction and rotation constants for four isomers of (Z)-1-chloro-2fluoroethylene-HCCH (shown in Fig. 2) obtained from ab initio calculations.

Structure

Relative energy/cm−1 no BSSE correction

with BSSE correction

A/MHz

B/MHz

C/MHz

a

115

80

11482

807

754

b

86

150

3286

1475

1184

c

0

0

4813

1096

893

d

107

72

3782

1128

914


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


Table 2. Spectroscopic constants (in MHz, unless as otherwise noted) for isotopologues of the (Z)-1-chloro-2-fluoroethylene−HCCH complex containing the most abundant and doubly substituted HCCH.a,b

CHFCH35Cl−HCCH

CHFCH35Cl−H13C13CH

CHFCH37Cl−HCCH

CHFCH37Cl−H13C13CH

A

4885.649228( 99)

4844.133223(90)

4742.466900(91)

4702.44026(10)

B

1057.174187(18)

1009.347259(33)

1056.557046(22)

1008.547284(51)

C

869.413273(16)

835.578516(29)

864.330083(17)

830.692831(49)

1.07966(19)

1.15677(12)

1.07287(30)

∆ J / 10-3

1.164334(94)

∆ JK / 10-3

−0.8488(22)

−0.8306(17)

−0.5401(32)

−0.5240(32)

∆ K / 10-3

69.855(14)

68.0776(94)

65.6213(87)

63.931(12)

δ J / 10-3

0.252150(37)

0.22633(11)

0.255032(56)

0.22912(14)

δ K / 10

5.2568(29)

4.987(11)

5.1816(48)

4.928(20)

Φ JK / 10-6

0.192(13)

0.192c

0.197(26)

0.197d

Φ KJ / 10-6

−1.891(96)

−1.891c

Φ K / 10-6

4.18(61)

4.18c

-3

−1.72(17) 4.18c

χaa (Cl)

39.83583(52)

39.85303(72)

31.40525(55)

χ bb (Cl)

−72.66213(65)

−72.67851(87)

−57.27398(65)

χ cc (Cl)

32.82630(59)

32.82549(77)

25.86873(58)

−1.72d 4.18c 31.41735(96) −57.2854(10) 25.86803(96)

No. of rotational transitions

156

99

123

78

No. of a type

69

48

57

38

No. of b type

87

51

66

40



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

No. of hyperfine components

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906

548

641

386

J range

0 – 12

0 – 11

0 – 11

0 – 10

Ka range

0–5

0–3

0–4

0–3

rms / kHz

a

1.68

1.79

1.74

1σ standard deviations in the parameters are given in parentheses.

b

The nuclear quadrupole coupling constants of chlorine are fitted as 1.5 χaa and ( χ bb − χ cc )/4, and the Laplace condition is used to

calculate the individual hyperfine constants. c

1.37

Fixed to the value appropriate for CH35ClCHF−HCCH.

d



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Table 3. Spectroscopic constants (in MHz, unless as otherwise noted) for isotopologues of the (Z)-1-chloro-2-fluoroethylene−HCCH complex containing a singly substituted 13C.a,b

13

CHFCH35Cl −HCCH

CHFCH35Cl−HC13CH

CHFCH35Cl−H13CCH

CHFCH37Cl−H13CCH

A

4822.9238(18)

4845.88104(16)

4884.42333(16)

4741.49292(17)

B

1052.27422(55)

1028.866544(68)

1036.106107(72)

1035.423877(82)

C

864.10317(37)

848.952452(41)

855.087226(42)

850.115187(48)

1.1127(88)

1.13659(62)

1.10508(67)

1.09794(69)

∆ J / 10-3 ∆ JK / 10-3

−0.986(86)

−1.025(10)

−0.6663(86)

−0.346(11)

∆ K / 10-3

67.63(42)

68.427(25)

69.591(25)

65.372(28)

δ J / 10-3

0.2288(39)

0.24293(35)

0.23374(38)

0.23723(40)

δ K / 10

5.2568c

5.2568c

5.2568c

5.1816d

Φ JK / 10-6

0.192c

0.192c

0.192c

0.197d

Φ KJ / 10-6

−1.891c

−1.891c

−1.891c

−1.72d

Φ K / 10-6

4.18c

4.18c

4.18c

4.18c

-3

χaa (Cl)

39.8319(81)

39.8622(12)

39.8278(12)

31.4007(17)

χ bb (Cl)

−72.6702(36)

−72.6824(12)

−72.6581(12)

−57.2709(15)

χ cc (Cl)

32.8383(60)

32.8201(11)

32.8302(11)

25.8702(15)

No. of rotational transitions

11

29

32

28

No. of a type

2

12

13

12

No. of b type

9

17

19

16



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

No. of hyperfine components

Page 24 of 31

30

152

171

120

J range

1–7

0–8

0–8

0–8

Ka range

0–2

0–3

0–3

0–3

rms / kHz

a

1.41

1.46

1.41

1σ standard deviations in the parameters are given in parentheses.

b

The nuclear quadrupole coupling constants of chlorine are fitted as 1.5 χaa and ( χ bb − χ cc )/4, and the Laplace condition is used to

calculate the individual hyperfine constants. c

1.61

Fixed to the value appropriate for CH35ClCHF−HCCH (see Table 2).

d



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Table 4. The coordinates of four atoms determined from a Kraitchman analysis and a structural fit. C-2 labels the carbon atom bonded to F in the (Z)-1-chloro-2-fluoroethylene subunit whereas C-3 and C-4 label the two carbon atoms in the HCCH subunit, with C-3 connected to the hydrogen that forms an interaction with Cl. C-2

Cl

C-3

C-4

(i) Substitution coordinatesa

a /Å

1.4938(10)

0.3759(40)

3.12715(48)

3.63357(41)

b /Å

1.1669(13)

1.2627(12)

0.1637(92)

0.9402(16)

0.3713

−3.1362

−1.2659

−0.1534

−3.6416 0.9441

(ii) From structural fit a/Å 1.4998 b/Å 1.1693 a

Costain errors26 in the parameters are given in parentheses.



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Figure 1. The electrostatic potential, mapped onto a total electron density isosurface for (a) vinyl fluoride, (b) 1,1,2-trifluoroethylene, and (c) (Z)-1-chloro-2-fluoroethylene. The same value of electron density is used for the isosurface in all molecules and identical color scales are used. Blue color represents positive electrostatic potential and red, negative electrostatic potential.


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Figure 2. The lowest-energy structures of (Z)-1-chloro-2-fluoroethylene–HCCH as determined by ab initio calculation. (See text for details.) The carbon atoms are dark gray, hydrogen atoms are light gray, the fluorine atom is light blue, and the chlorine atom is green.



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Figure 3. (a) A portion of the chirped pulse spectrum showing transitions from (Z)CHFCH35Cl−HCCH (red) and (Z)-CHFCH37Cl−HCCH (blue). The transitions that are not marked are mostly due to (Z)-CHFCH35Cl, Ar-(Z)-CHFCH35Cl−HCCH, and Ar-(Z)-


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CHFCH37Cl−HCCH. The hyperfine components of the HCCH complexes are connected by a comb and labeled with J′ Ka’ Kc’ – J″ Ka″ Kc″. The blue star identifies the 616 – 515 transition in (Z)-CHFCH37Cl−HCCH. The boxed region is expanded in (b), where the red stars identify the hyperfine components due to the 422 – 413 transition in (Z)-CHFCH35Cl−HCCH. Those for the 616 – 515 transition of the same isotopologue are not resolved in this spectrum. (c) A 0.75 MHz Balle-Flygare spectrum showing four Doppler doubled hyperfine components of the 616 – 515 transition [purple, unresolved in (b)] and one component of the 422 – 413 transition (green), both in (Z)-CHFCH35Cl−HCCH.



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Figure 4. The structures of (a) (Z)-1-chloro-2-fluoroethylene-HCCH (this work) and (b) vinyl chloride-HCCH.5 The carbon atoms are dark gray, hydrogen atoms are light gray, the fluorine atom is light blue, and the chlorine atom is green.


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