Chlorine Nuclear Quadrupole Coupling Constants Research Articles

Internal rotation and chlorine nuclear quadrupole coupling in 2-chloro-4-fluorotoluene explored by microwave spectroscopy and quantum chemistry.

2-Chloro-4-fluorotoluene was investigated using a combination of molecular jet Fourier transform microwave spectroscopy in the frequency range from 5 to 21GHz and quantum chemistry. The molecule experiences an internal rotation of the methyl group, which causes fine splittings of all rotational transitions into doublets with separation on the order of a few tens of kHz. In addition, hyperfine effects originating from the chlorine nuclear quadrupole moment coupling its nuclear spin to the end-over-end rotation of the molecule are observed. The torsional barrier was derived using both the rho and the combined-axis-method, giving a value of 462.5(41) cm-1. Accurate rotational constants and quadrupole coupling constants were determined for the 35Cl and 37Cl isotopologues and compared with Bailey's semi-experimental quantum chemical predictions. The gas phase molecular structure was deduced from the experimental rotational constants supplemented with those calculated by quantum chemistry at various levels of theory. The values of the methyl torsional barrier and chlorine nuclear quadrupole coupling constants were compared with the theoretical predictions and with those of other chlorotoluene derivatives.

Observation of a double C–H⋯π interaction in the CH2ClF⋯HCCH weakly bound complex

The structure of the CH(2)ClF···HCCH dimer has been determined using both chirped-pulse and resonant cavity Fourier-transform microwave spectroscopy. The complex has C(s) symmetry and contains both a double C-H···π interaction, in which one π-bond acts as acceptor to two hydrogen atoms from the CH(2)ClF donor, and a weak C-H···Cl interaction, with acetylene as the donor. Analysis of the rotational spectra of four isotopologues (CH(2)(35)ClF···H(12)C(12)CH, CH(2)(37)ClF···H(12)C(12)CH, CH(2)(35)ClF···H(13)C(13)CH, and CH(2)(37)ClF-H(13)C(13)CH) has led to a structure with C-H···π distances of 3.236(6) Å and a C-H···Cl distance of 3.207(22) Å, in good agreement with ab initio calculations at the MP2/6-311++G(2d,2p) level. Both weak contacts are longer than those observed in similar complexes containing a single C-H···π interaction that lies in the C(s) plane; however, this appears to be the first double C-H···π contact to be studied by microwave spectroscopy, so there is little data for direct comparison. The rotational and chlorine nuclear quadrupole coupling constants for the most abundant isotopologue are: A = 5262.899(14) MHz, B = 1546.8074(10) MHz, C = 1205.4349(7) MHz, χ(aa) = 28.497(5) MHz, χ(bb) = -65.618(13) MHz, and χ(cc) = 37.121(8) MHz.

Microwave spectra of eight isotopic modifications of 1-chloro-1-fluoroethylene

The rotational spectra of eight isotopomers of 1-chloro-1-fluoroethylene in the 6–22 GHz region have been collected and analyzed. Each rotational transition is split into hyperfine components by the chlorine (either 35Cl or 37Cl) nuclear quadrupole coupling interaction and additionally, one or more smaller interactions such as the spin–rotation interaction due to the fluorine atom, hydrogen–hydrogen spin–spin coupling interactions, and in appropriately substituted species, the deuterium nuclear quadrupole hyperfine interaction. The rotational constants derived from these isotopomers allow the determination of average and Kraitchman substitution structures for 1-chloro-1-fluoroethylene, whereas the availability of the diagonal chlorine nuclear quadrupole coupling constants for all the isotopomers provides complete quadrupole coupling tensors for both 35Cl and 37Cl. In the course of this work, the rotational spectrum of an excited vibrational state of the normal isotopomer was observed, which ab initio calculations suggest should be assigned to ν 9 = 1 , an in-plane bending motion at the CFCl end of the molecule.

The pure rotational spectrum of pivaloyl chloride, (CH 3) 3CCOCl, between 800 and 18 800 MHz

A search accelerated correct intensity Fourier transform microwave (SACI-FTMW) spectrometer has been used to rapidly record the rotational spectrum of pivaloyl chloride between 8 and 18 GHz. Both a radio frequency and regular cavity-based instrument have then been used to obtain high resolution measurements below 4 GHz and in the 4–18 GHz regions, respectively. Rotational constants, centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants have been determined for both the 35Cl and 37Cl isotopologues. The spectrum provides no evidence concerning internal rotation in the molecule.

Conformation and Intramolecular Hydrogen Bonding of 2-Chloroacetamide as Studied by Microwave Spectroscopy and Quantum Chemical Calculations

The microwave spectrum of 2-chloroacetamide (ClCH2CONH2) has been investigated at room temperature in the 19-80 spectral range. Spectra of the 35ClCH2CONH2 and 37ClCH2CONH2 isotopomers of one conformer, which has a symmetry plane (Cs symmetry), were assigned. The amide group is planar, and an intramolecular hydrogen bond is formed between the chlorine atom and the nearest hydrogen atom of the amide group. The ground vibrational state, six vibrationally excited states of the torsional vibration about the CC bond, as well as the first excited state of the lowest bending mode were assigned for the 35ClCH2CONH2 isotopomer, whereas the ground vibrational state of 37ClCH2CONH2 was assigned. The CC torsional fundamental vibration has a frequency of 62(10) cm(-1), and the bending vibration has a frequency of 204(30) cm(-1). The rotational constants of the ground and of the six excited states of the CC torsion were fitted to the potential function Vz = 16.1(<z4> + 2.3<z2>) cm(-1), where z is a dimensionless parameter. This function indicates that the equilibrium conformation has Cs symmetry. Rough values of the chlorine nuclear quadrupole coupling constants were derived as chi(aa) = -47.62(52) and chi(bb) = 8.22(66) MHz for the 35Cl nucleus and chi(aa) = -34.6(10) and chi(bb) = 6.2(11) MHz for the 37Cl nucleus. Ab initio and density functional theory quantum chemical calculations have been performed at several levels of theory to evaluate the equilibrium geometry of this compound. The density functional theory calculations at the B3LYP/6-311++G(3df,2pd) and B3LYP/cc-pVTZ levels of theory as well as ab initio calculations at the MP2(F)/cc-pVTZ level predict correct lowest-energy conformation for the molecule, whereas the ab initio calculations at the QCISD(FC)/6-311G(d) and MP2(F)/6-311++G(d,p) levels predict an incorrect equilibrium conformation.

Hyperfine Interactions in HSiCl

The J = 1−0 transitions of the microwave spectra of H28Si35Cl, H28Si37Cl, H29Si35Cl, and H30Si35Cl were measured at 14−15 GHz. The effective rotational constants are obtained, and the chlorine nuclear quadrupole coupling constants and nuclear spin-rotation constants of the four isotopomers are determined for the first time. These constants are compared with their values obtained from ab initio calculations.

Residual 31P, 35,37Cl Dipolar Coupling in 31P MAS Spectra of Chlorocyclophosphazenes

In 31P MAS NMR spectra of chlorocyclophosphazenes, characteristic splittings have been observed for PCl or PCl2 groups. At different applied magnetic fields, the fine structure and total width of the patterns change in a characteristic way, demonstrating that the splittings are due to indirect spin–spin and residual dipolar interactions with the chlorine nuclei directly bonded to phosphorus. For trans-nongeminal N3P3Cl3(NMe2)3 and N3P3Cl6 as examples, the spectra have been analyzed to obtain information on chlorine nuclear quadrupole coupling constants and 35,37Cl, 31P indirect spin–spin coupling constants. Neglect of these interactions may result in misinterpretations of the multiplicity in 31P MAS spectra of chlorophosphazenes.

Microwave Spectrum, Structure, and Hyperfine Constants of Kr–AgCl: Formation of a Weak Kr–Ag Covalent Bond

The pure rotational spectrum of the complex Kr–AgCl has been measured between 8–15 GHz using a cavity pulsed-jet Fourier transform microwave spectrometer. The complex was found to be linear and relatively rigid, with a Kr–Ag bond length of ∼2.641 Å. The Kr–Ag stretching frequency was estimated to be 117 cm−1. Ab initio calculations performed at the MP2 level of theory gave the geometry, vibration frequencies, Kr–Ag bond dissociation energy, and orbital populations. The Kr–Ag bond dissociation energy was estimated to be ∼28 kJ mol−1. The Kr–Ag force constant and dissociation energy are greater than those of Ar–Ag in Ar–AgCl. The chlorine nuclear quadrupole coupling constants show slight changes on complex formation. Ab initio orbital population analysis shows a small shift in σ-electron density from Kr to Ag on complex formation. The combined experimental and ab initio results are consistent with the presence of a weak Kr–Ag covalent bond.

Structure of the chlorobenzene–argon dimer: Microwave spectrum and ab initio analysis

The rotational spectra of the Cl35 and Cl37 isotopes of the chlorobenzene–argon van der Waals dimer have been assigned using Fourier transform microwave spectroscopy techniques. Rotational constants and chlorine nuclear quadrupole coupling constants were determined which confirm that the complex has Cs symmetry. The argon is over the aromatic ring, shifted from a position above the geometrical ring center towards the substituted carbon atom, and at a distance of about 3.68 Å from it. This distance is 0.1–0.2 Å shorter than the similar distance in the benzene–argon and fluorobenzene–argon complexes. Experimental results are confirmed and explained with the help of second-order Mo/ller–Plesset perturbation calculations using a VDZP+diff basis set. The complex binding energy of the chlorobenzene–argon complex is 1.28 kcal/mol (fluorobenzene–argon, 1.17; benzene–argon, 1.12 kcal/mol) reflecting an increase in stability caused by larger dispersion interactions when replacing one benzene H atom by F or by Cl. The structure and stability of Ar⋅C6H5–X complexes are explained in terms of a balance between stabilizing dispersion and destabilizing exchange repulsion interactions between the monomers.

Rotational Spectrum and Structure of 1,2-Dichloro-3,3,4,4-tetrafluorocyclobutene: Comparison of Spectroscopy, Diffraction, and ab Initio Results

The rotational spectra of four isotopomers of 1,2-dichloro-3,3,4,4-tetrafluorocyclobutene have been measured with a Fourier transform microwave spectrometer. The ring parameters determined from the inertial data were r(C1C2) = 1.311(15) Å, r(C2C3) = 1.487(15) Å, and r(C3C4) = 1.551(15) Å, with the angles (C1C2C3) = 94.6(6)° and (C2C3C4) = 85.4(6)°. The C3C4 bond is found to be shorter by 0.05 Å than the value obtained from an electron diffraction study, although consistent with a previous microwave study of the closely related molecule hexafluorocyclobutene. The C1C2 bond is also 0.04 Å shorter than the electron diffraction data and about 0.02−0.03 Å shorter than microwave spectroscopy studies of other tetrafluorocyclobutenes. The reasons for these differences are unclear. The chlorine nuclear quadrupole coupling constants were determined; the axis of the principal nuclear quadrupole coupling tensor is essentially parallel to the carbonchlorine bond axis. Comparisons with theoretical calculations and electron diffraction results are made, along with comparisons with similar molecules.

Inter- and intramolecular electron transfer in the complex OC···ICl determined from iodine and chlorine nuclear quadrupole hyperfine structure in its rotational spectrum

The ground-state rotational spectra of three isotopomers O12C···I35Cl, O12C···I37Cl and O13C···I35Cl of a linear (or quasi-linear) complex formed by carbon monoxide and iodine monochloride were observed by using a pulsed-nozzle, Fourier transform microwave spectrometer. The spectroscopic constants B0, DJ, χaa(I), χaa(Cl) and Mbb(I) were determined for each isotopomer. Simple models were used to interpret the spectroscopic constants to give details of the geometry, binding strength and electric charge redistribution in OC···ICl. It was concluded that the nuclei lie in the order OC···ICl with the distance r(C···I)=3.011(1) A, that the quadratic intermolecular stretching force constant kσ=8.00(3) N m-1, and that, when CO achieves its equilibrium position in the complex, the changes in the iodine and chlorine nuclear quadrupole coupling constants of ICl are consistent with the transfer of a fraction δ1=0.025(2) of an electronic charge from C to I and an intramolecular transfer of a fraction δ2=0.048(2) from I to Cl. A comparison of the r(C···X), kσ and δ2 values for the series of complexes OC···XY, where XY=ClF, Cl2, BrCl, Br2 and ICl is presented. The order of kσ is ICl>ClF>BrCl>Br2>Cl2, while the order of δ2 is Cl2∽ClF<Br2∽BrCl<ICl. It is deduced that ICl is ‘snub-nosed’, i.e. the I atom has a smaller van der Waals radius along the ICl internuclear axis than perpendicular to it.

The Microwave Spectrum of 2-Chloro-1,1,1,2-Tetrafluoroethane

The microwave spectrum of 2-chloro-1,1,1,2-tetrafluoroethane has been analyzed in the frequency region 12–52 GHz using waveguide Fourier transform and Stark modulation microwave spectrometers. The spectra of35Cl and37Cl isotopomers and of the two lowest excited states of the CF3torsional vibration of35Cl species have been measured up toJ= 58. Chlorine nuclear quadrupole coupling constants have been determined from a first-order analysis of the observed hyperfine components. Rotational constants and quartic centrifugal distortion constants have been determined from the calculated central frequencies. Relative intensity measurements give a value of 4.0 ± 1.8 kcal mole−1for the barrier to internal rotation of CF3group.

The Millimeter-Wave Spectrum of cis-1,2-Dichloroethylene

The rotational spectra of the 35Cl 35Cl, 35Cl 37Cl, and 37Cl 37Cl isotopomers of cis- 1,2-dichloroethylene have been observed in the frequency range 12.4-246 GHz. Accurate rotational constants and all the quartic and sextic centrifugal distortion constants have been obtained from semirigid rotor fits to the central line frequencies corrected for the chlorine nuclear quadrupole coupling. The chlorine nuclear quadrupole coupling constants of the 35Cl 35Cl, 35Cl 37Cl, and 37Cl 37Cl isotopomers have been determined.

The Millimeter-Wave Spectra of 1-Chloro-1-fluoroethylene and cis-1-Chloro-2-fluoroethylene

The ground vibrational state microwave spectra of the 35Cl and 37Cl isotopomers of 1-cbloro-1-fluoroethylene and cis-l-chloro-2-fluoroethylene have been studied in the frequency range 26-245 GHz. Chlorine nuclear quadrupole coupling constants have been obtained from first-order analyses of the frequencies of 100 hyperfine components for each isotopomer. Rotational constants and quartic and sextic centrifugal distortion constants have been determined from fits to large numbers of central transition frequencies. A brief description of the computer-controlled source modulation millimeter-wave spectrometer used in this work is given.

Identification and characterisation of the gas-phase complex HCN⋯Cl2by rotational spectroscopy

The ground-state rotational spectra of three isotopomers, HC15N⋯35Cl2, HC15N⋯37Cl35Cl and HC15N⋯35Cl37Cl, of the linear complex HCN⋯Cl2 have been observed by the pulsed-nozzle, Fourier-transform microwave technique and analysed to give the rotational constant B0, the centrifugal distortion constant DJ, and the chlorine nuclear quadrupole coupling constants χ(Cli) and χ(Clo) in each case. A B0 value has also been estimated for the isotopomer HC 14N⋯35Cl2. The distances r(N⋯Cli), r(N⋯Clo) and r(Cl—Cl) have been determined from the rotational constants (i denotes ‘inner’, o, ‘outer’). The small value of kσ, the intermolecular stretching force constant, estimated from DJ, and the small difference Δχ(35Cl)=χ(35Cli)–χ(35Clo) are interpreted in terms of only a small perturbation of the Cl2 subunit on complex formation. A comparison of the properties of the four dimers B⋯Cl2, where B = CO, HF, PH3 and HCN, with those of the corresponding series B⋯HCl of hydrogen-bonded complexes indicates a parallel behaviour in the two series. The propensity of Cl2 to form complexes with B, as measured by its gas-phase electrophilicity E, is compared with that of HCl.

Cl-nuclear quadrupole coupling in the microwave spectra of 1-chloroadamantane and t-butyl chloride

The nuclear quadrupole hyperfine structure in each of the species 1- 35,37Cl-chloroadamantane and (CH 3) 3C- 35,37Cl is analysed to give chlorine nuclear quadrupole coupling constants, rotational constants and centrifugal distortion constants.

Deuterium Quadrupole Coupling Constants in Deuterochloroacetylene

Abstract The deuterium and chlorine nuclear quadrupole coupling constants have been determined for both of the chlorine isotopomers of deuterochloroacetylene (DCCC1), along with the rotational, centrifugal distortion, and chlorine spin-rotation coupling constants. The values are B = 5186.97631 (22) MHz, DJ= 1.13(2) kHz, eQq(Cl)= -79.7358(19) MHz, cI(Cl) = 1.10(31)kHz, and eQq(D) = 207.0(28)kHz for DCCCl-35, and B = 5084.17839(30) MHz, DJ = 0.99(2) kHz, eQq(Cl)= -62.8451(27) MHz, cI(CI) = 0.76(43) kHz, and eQq(D) = 205.8(39)kHz for DCCCl-37.

The microwave spectrum, harmonic force field and structure of chlorodifluoromethane, CHF 2Cl

Rotational spectra of four isotopic species of chlorodifluoromethane, CHF 2 35Cl, CHF 2 37Cl, CDF 2 35Cl and CDF 2 37Cl, have been extensively measured, and have been analysed for rotational constants, centrifugal distortion constants and chlorine nuclear quadrupole coupling constants. The distortion constants have been combined with vibrational wavenumbers from the literature and with ab initio force constants calculated in the present work to refine the harmonic force field. Ground state effective ( r 0), substitution ( r s) and ground state average ( r z) structures have been evaluated for the molecule.

The microwave spectrum, harmonic force field, and structure of carbonyl chlorofluoride, OCCIF

Rotational spectra of three isotopic species of carbonyl chlorofluoride, OCCIF, have been extensively measured, and have been analyzed for rotational constants, quartic centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants. Ab initio calculations of the harmonic force field have been made using several different sets of basis functions, and their relative cost efficiency has been assessed. The measured distortion constants have been combined with vibrational wavenumbers (both from the literature and from the present work) and with the ab initio force constants to refine the force field. Ground state effective ( r 0) and average ( r z ) structures have been evaluated for the molecule.

The microwave and millimeter-wave spectra of hypochlorous acid

To permit atmospheric monitoring of the molecule, the microwave spectra of two isotopic species of hypochlorous acid, HOCl, have been measured in the frequency range 8–650 GHz. Three b-type branches and an a-type Q branch have all been measured for the first time; improved measurements have been made for the a-type R branches. The analysis has included combination differences of earlier high-resolution infrared spectra to give accurate values for all rotational constants, five quartic and five higher degree centrifugal distortion constants, as well as the chlorine nuclear quadrupole and spin-rotation coupling constants. From the Stark effect, accurate values have also been obtained for both components of the molecular dipole moment. A table of transition frequencies of potential use in atmospheric monitoring is presented.