Rotational spectroscopy and molecular structure of the 1,1-difluoroethylene-acetylene complex

Fourier transform microwave, rotational spectra in the 6-21 GHz region are obtained for the complex formed between 1,1-difluoroethylene and acetylene, including the normal isotopomer and each singly substituted (13)C species along with complexes derived from commercially available isotopic varieties of acetylene (HCCD, DCCD, and H(13)C(13)CH). Although two possible planar structures are consistent with the rotational constants derived from analysis of the spectra, ab initio calculations, as well as chemical intuition, support only one of the two as the structure of the complex. Nuclear quadrupole coupling constants for D-containing species show no evidence of electric field gradient perturbation and are consistent with the structures obtained from inertial data. The primary interaction between the two molecules is a 2.646(11) A hydrogen bond with acetylene as the donor and a 1,1-difluoroethylene fluorine as the acceptor that forms a 122.41(79) degrees C-Fcdots, three dots, centeredH angle. A secondary interaction between the acetylenic bond and the difluoroethylene hydrogen atom cis to the acceptor fluorine atom causes the hydrogen bond to deviate 53.25(24) degrees from linearity. Structural comparisons with the related complex, 1,1-difluoroethylene-hydrogen chloride [Z. Kisiel et al., J. Chem. Soc., Faraday Trans. 88, 3385 (1992)], suggest that the hydrogen bond in the acetylene complex is weaker, whereas comparisons with vinyl fluoride-acetylene [G. C. Cole and A. C. Legon, Chem. Phys. Lett. 369, 31 (2003)] indicate that the fluorine atoms in 1,1-difluoroethylene are less basic than the one in vinyl fluoride.     

Rotational spectroscopy and molecular structure of the 1,1,2-trifluoroethylene-acetylene complex

Guided by ab initio calculations, Fourier transform microwave rotational spectra in the 6-22 GHz region are obtained for the complex formed between 1,1,2-trifluoroethylene and acetylene, including the normal isotopomer, three of four singly substituted (13)C species obtained in natural abundance, and using commercially available isotopic varieties of acetylene, species containing HCCD and H(13)C(13)CH. Although the ab initio calculations suggest two possible low energy planar arrangements for the molecules in the complex, only a single, unique structure is obtained from a combined analysis of the rotational constants derived from the spectra and atomic positions determined using Kraitchman [Am. J. Phys. 21, 17 (1953)] substitution coordinates. This structure is similar to that obtained for the CF(2)CHF[Single Bond]HF complex [H. O. Leung and M. D. Marshall, J. Chem. Phys. 126, 114310 (2007)] in which both the primary and secondary interactions occur between the HCCH molecule and a F atom and a H atom bonded to the same carbon of CF(2)CHF. The 2.748(15) A hydrogen bond has acetylene as the donor and 1,1,2-trifluoroethylene as the acceptor and forms a 104.49(15) degrees C[Single Bond]Fcdots, three dots, centeredH angle. The 2.8694(9) A secondary interaction between the pi bond of acetylene and the H atom geminal to the acceptor F atom causes the hydrogen bond to deviate 69.24(67) degrees from linearity. This large deviation from linearity and the similarity of the two intermolecular bond lengths suggest that the two interactions are becoming comparable in importance.     

Rotational spectroscopy and molecular structure of 1,1,2-trifluoroethylene and the 1,1,2-trifluoroethylene-hydrogen fluoride complex

Fourier transform microwave rotational spectra in the 6-22 GHz region are obtained for the complex formed between 1,1,2-trifluoroethylene and hydrogen fluoride, including the normal isotopomer, the two singly substituted 13C species, and the complex obtained with DF. A unique planar structure for the complex is determined from a combined analysis of the rotational constants derived from the spectra and atomic positions obtained using Kraitchman [Am. J. Phys. 21, 17 (1953)] substitution coordinates. Consistent with this structure, no hyperfine splitting of rotational lines due to the nuclear quadrupole coupling interaction is observed for the D-containing species. Although the primary interaction in the complex is a hydrogen-fluorine hydrogen bond, as is the case for all previously studied Lewis acid-fluoroethylene complexes, the CF2CHF-HF complex adopts a distinctly different geometry in which both the primary and secondary interactions occur between the HF molecule and a F atom and a H atom, respectively, bonded to the same carbon of CF2CHF. The 2.020(41) A hydrogen bond has hydrogen fluoride as the donor and 1,1,2-trifluoroethylene as the acceptor and forms a 109.0(13) degrees C-F...H angle. The secondary interaction between the hydrogen fluoride F atom and the H atom geminal to the acceptor F atom causes the hydrogen bond to deviate 41.6(51) degrees from linearity. Structural comparisons with analogous complexes formed with mono- and difluorinated ethylenes suggest that the primary hydrogen bond strength and the fluoroethylene fluorine atom basicity both decrease with increasing fluorine substitution. In the course of this work, it was necessary to obtain additional rotational spectra for the 1,1,2-trifluroethylene monomer and to improve the precision of the values of the structural parameters for this molecule.     

Rotational spectroscopy of jet-cooled molecular ions and ion complexes

Rotational spectra of the molecular ions HOCO⁺ and HOCS⁺, and the ion complexes, D₃⁺Ar and sym-D₂H⁺Ar were observed in a supersonic-jet expansion by using a Fabry-Perot type Fourier-transform microwave spectrometer cooperated with a pulsed discharge nozzle. Ion-formation efficiency for HOCS⁺ relative to the parent molecule under applied conditions was estimated to be ≈ 10⁻⁴. Tunneling splitting in the lowest rotational transition of D₃⁺-Ar was not resolved within the experimental linewidth of ≈ 100 kHz.     

Crystal structure of the 1:2 molecular complex between thecis-anti-cis isomer of dicyclohexano-18-crown-6 and 3-chloro-6-methylbenzenesulphamide

Reaction of thecis-anti-cis isomer of dicyclohexano-18-crown-6 with a mixture of 2-chloro-5-methylbenzenesulphamide and 3-chloro-6-methylbenzenesulphamide gives a crystalline product which has been characterized using X-ray crystallography. The complex (I) contains both isomers in a 83.0 (0.6):17.0 (0.6) ratio in favour of the 3-chloro-6-methyl-isomer. The joint crystallization of the crown ether with the mixture of the guest isomers might serve as a route for the partial extraction of one of them. The complex with host: guest ratio 1:2 crystallizes in a triclinic space group ,a=13.087(4),b=9.217(2),c=8.120(2) Å, =92.05(3),=100.52(3), =80.64(2)°, withZ=1. The structure was refined toR=0.041. Each of two equivalent guest molecules interacts with the macrocyclic ring by two NH...O hydrogen bonds, with N...O distances of 2.912(5) and 3.040(5) Å. Supplementary Data relevant to this paper have been deposited with the British Libary as Supplementary Publication No. SUP 82180 (30 pp.).     

Crystal and molecular structure of 4-chloro-7-diethylaminocoumarin

An x-ray study of 4-chloro-7-diethylaminocoumarin was carried out. The introduction of an electron-withdrawing substituent at C⁴ leads to localization of the double bond in the pyran ring and equalization of the bond lengths in the benzene ring.A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. K. A. Timiryazev All-Union Agricultural Academy, 127550 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 445–448, February, 1992.     

Rotational viscosity and molecular structure of nematic liquid crystals

An electro-optical technique was used to measure the rotational viscosity of nematic liquid crystals, whose structures were chosen to investigate the effects of linking groups and lateral groups on rotational viscosity. These results are compared with the theory developed by Osipov and Terentjev. It is shown that the theory is useful in predicting rotational viscosity for specific molecular structures. The agreement between theory and experiment is found to be good for all the liquid crystals studied.     

Crystal and molecular structure of 2-chloro-1-methyl-4-phenyl-α-carboline hydrochloride

A compound with the composition C₁₈H₁₆Cl₂ON₂ was subjected to an x-ray diffraction study. All of the rings in themolecule are planar. Both of the six-membered rings of the carboline system are inclined slightly and identically with respect to the central pyrrole ring, forming angles of 3 ° with it and 6 ° with one another. The phenyl ring is turned at an angle of 52.7 ° relative to the average plane of the carboline system.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp, 779–782, June, 1984.     

Application of X-ray photoelectron spectroscopy for studying the molecular structure of corrosion inhibitor — Zinc complex of 1-hydroxyethylidene diphosphonic acid

The molecular structure of zinc complex of 1-hydroxyethylidene diphosphonic acid was studied by X-ray photoelectron spectroscopy. The obtained data were compared with IR absorption spectrum of the same substance to acquire new information on the molecular structure. It was shown that coordination of the phosphonate group by zinc atom retains the localization of P-O π bond, the phosphonate group does not have a third-order axis of symmetry, and Zn atom can occupy positions with different coordination. Thermal destruction of the complex is accompanied by decomposition of hetero-organic ligand with detachment of the hydrocarbon fragment along C-P bonds and formation of inorganic zinc salts.     

A study on the anisole-water complex by molecular beam-electronic spectroscopy and molecular mechanics calculations

An experimental and theoretical study is made on the anisole-water complex. It is the first van der Waals complex studied by high resolution electronic spectroscopy in which the water is seen acting as an acid. Vibronically and rotationally resolved electronic spectroscopy experiments and molecular mechanics calculations are used to elucidate the structure of the complex in the ground and first electronic excited state. Some internal dynamics in the system is revealed by high resolution spectroscopy.     

Rotational spectra of 1-chloro-2-fluoroethylene. II. Equilibrium structures of the cis and trans isomer

Equilibrium structures for the cis and trans isomer of 1-chloro-2-fluoroethylene are reported. The structures are obtained within a least-squares fit procedure using the available experimental ground-state rotational constants for various isotopic species of both forms. Vibrational effects were eliminated before the analysis using vibration-rotation interaction constants derived from computed quadratic and cubic force fields with the required quantum chemical calculations carried out using second-order Moller-Plesset perturbation as well as coupled-cluster (CC) theory. The semiexperimental or empirical equilibrium geometries obtained in this way agree well with the corresponding theoretical predictions obtained from CC calculations [at the CCSD(T) level] after extrapolation to the complete basis-set limit and inclusion of core-valence correlation corrections. The present results allow a detailed analysis of the geometrical differences between the two forms of 1-chloro-2-fluoroethylene. They are also compared to the structural data available for other halogenated ethylenes.     

3-chloro-1-butene: gas-phase molecular structure and conformations as determined by electron diffraction and by molecular mechanics and ab initio calculations

Gaseous 3-chloro-1-butene has been studied experimentally by electron diffraction (ED) at 20 and 180°C, and at these temperatures, 76(10)% and 62(10)%, respectively, of the most stable conformer i.e. the one having a hydrogen atom eclipsing the double bond, were found. The conformer with the chlorine atom eclipsing the C=C bond was also present. However, from the experimental data it was not possible to establish conclusive evidence for the conformer with an eclipsed CH₃ group. Molecular mechanics (MM) calculations and ab initio calculations using a 4-21 basis set were carried out with complete geometry optimization, and calculated parameters from each of the methods were used in combination with the ED data. Such calculations indicated the existence of all three conformers mentioned above. Least-squares analysis including constraints from the ab initio calculation gave as a result the following molecular structure (r_a distances and ??? angles) for the predominant conformer: r(C=C) = 1.337(6) Å, r(=C---C) = 1.503(4) Å, r(C---CH₃) = 1.522 Å, R(C---Cl) = 1.813(4) Å, <r(C---H)> = 1.089(18) Å, ???C=C---C = 122.9(2.1)°, ???C---C---C = 112.6(2.2)°, ???=C---C---Cl = 109.9(0.2)°, ???Cl---C---CH₃ = 109.3°. = 121.9° and = 110.0(1.3)°. The torsional angles were then τ(C=C---C---Cl> = −119.4° and τ(C=C---C---CH₃) = 120.3(2.1)°. Error limits are 2σ (σ includes estimates of systematic errors and correlations), parameters without quoted uncertainties are dependent or were constrained relative to another parameter. Combining the ED data with MM results yielded parameters consistent with those given above.