Rotational spectroscopy and molecular structure of the 1-chloro-1-fluoroethylene-acetylene complex

Abstract

Guided by ab initio calculations, Fourier transform microwave spectra in the 6-21 GHz region are obtained for seven isotopomers of the complex formed between 1-chloro-1-fluoroethylene and acetylene. These include the four possible combinations of (35)Cl- and (37)Cl-containing CH(2)CClF with the most abundant acetylene isotopic modification, HCCH, and its H(13)C(13)CH analogue, as well as three singly substituted deuterated isotopomers. Analysis of the spectra determines the rotational constants and additionally, the complete chlorine quadrupole hyperfine coupling tensors in both the inertial and principal electric field gradient axis systems, and where appropriate, the diagonal components of the deuterium quadrupole coupling tensors. The inertial information contained in the rotational constants provides the structure for CH(2)CClF-HCCH: a primary, hydrogen bonding interaction existing between the HCCH donor and the F atom acceptor on the 1-chloro-1-fluoroethylene moiety, while a secondary interaction occurs between the acetylenic bond on the HCCH molecule and the H atom cis to the hydrogen-bonded F atom on the substituted ethylene, which causes the hydrogen bond to deviate from linearity. This is similar to the structure obtained for 1,1-difluoroethylene-HCCH [H. O. Leung and M. D. Marshall, J. Chem. Phys. 126, 154301 (2006)], and indeed, to within experimental uncertainty, the intermolecular interactions in CH(2)CClF-HCCH and its 1,1-difluoroethylene counterpart are practically indistinguishable, even though ab initio calculations at the MP2∕6-311G++(2d, 2p) level suggest that the former complex is more strongly bound.

Microwave spectrum and molecular structure of the 1-chloro-1-fluoroethylene-hydrogen fluoride complex

“…1). Three are qualitatively similar to their HCCH counterparts [2]: with the acid hydrogen bonding to the F atom in the ethylene subunit and forming a secondary interaction with the H atom cis to the F atom [structure (a)]; a second structure with a hydrogen bond to the same F atom, but with the donor approaching from a different angle and with no secondary interaction [structure (b)]; and third, the acid hydrogen bonding to the Cl atom with a secondary interaction involving the H atom in the cis position [structure (c)]. It is interesting to note that relative energies of structures (b) and (c) are reversed as compared to the corresponding minima for CH 2 CClF-HCCH.…”

“…We have interpreted these results in terms of changes in F atom nucleophilicity caused by the differing degrees of substitution and the importance of attaining a balance between electrostatic and steric effects [1]. More recently, we have extended this work to consider not only fluorine, but also chlorine substitution in a study of the 1-chloro-1-fluoroethylene-acetylene complex, where we found that the intermolecular interactions in CH 2 CClF-HCCH were, within experimental uncertainty, indistinguishable from those of its 1,1-difluoroethylene counterpart, suggesting identical effects for geminal substitution of hydrogen in vinyl fluoride by either fluorine or the less electronegative, more polarizable chlorine [2]. This was at odds with theoretical predictions.…”

“…We restrict the different configurations of the complex to be planar, as observed spectroscopically for those of fluoroethylenecontaining complexes [1,[3][4][5][6][7][8][9][10][11][12] and for 1-chloro-1-fluoroethylene-HCCH [2]. The monomer geometries are held at their average values in the ground vibrational states [14,15].…”

“…In each case, as well as for trans-1,2-difluoroethylene-HF [1] and 1-chloro-1-fluoroethylene-HCCH [2], the complexes adopt a planar structure containing two non-covalent interactions: a primary, hydrogen bonding interaction between the protic acid and a fluorine atom on the substituted ethylene, and a secondary interaction, made possible by a deviation of the hydrogen bond from linearity, between a hydrogen atom in the substituted ethylene and the nucleophilic portion of the acid. Similarly, we expect that a determination of the structures of complexes of 1-chloro-1-fluoroethylene with additional protic acids will be valuable to our goal of a fuller understanding of the effects of chlorine substitution on intermolecular interactions.…”

A chirped pulse Fourier transform microwave study of the refrigerant alternative 2,3,3,3-tetrafluoropropene

“…We have recently extended this work to consider not only fluorine, but also chlorine substitution [19], and we also wish to investigate the effects of the increased degree of fluorine substitution that can occur in larger olefins. A complex formed between a protic acid and 2,3,3,3-tetrafluoropropene (TFP), when compared with the analogous vinyl fluoride or 1,1-difluoroethylene species, would show the consequences of replacing a hydrogen atom or a fluorine atom, respectively, by the -CF 3 moiety.…”