Marabeth S. LaBarge

Microwave spectrum, structure, barrier to internal rotation, dipole moment, and deuterium quadupole coupling constants of the ethylene-sulfur dioxide complex

The microwave spectra of the complex between ethylene and sulfur dioxide and nine of its isotopic species have been observed in a Fourier transform microwave spectrometer. The spectra exhibit a and c dipole selection rules; transitions of the normal species and several of the isotopically substituted species occur as tunneling doublets. The complex has a stacked structure with Cs symmetry; the C2H4 and SO2 moieties both straddle the mirror plane with the C2 axis of SO2 crossed at 90 ° to the carbon–carbon bond axis (i.e., only the S atom lies in the symmetry plane). The distance between the centers of mass (Rcm) of C2H4 and SO2 is 3.504(1) A and the deviation of their planes from perpendicular to Rcm is 21(2) ° and 12(2) °, respectively. The tunneling splittings arise from a rotation of the ethylene subunit in its molecular plane. The barrier to internal rotation is 30(2) cm−1. The dipole moment of the complex is 1.650(3)D. The deuterium nuclear quadrupole coupling constants for C2H3D⋅SO2 are χaa=−0.119(1) MHz, χbb=0.010(1) MHz, and χcc=0.109(1) MHz. The binding energy is estimated to be 490 cm−1 from the pseudo‐diatomic approximation. A distributed multipole electrostatic model is explored to rationalize the structure and binding energies.The microwave spectra of the complex between ethylene and sulfur dioxide and nine of its isotopic species have been observed in a Fourier transform microwave spectrometer. The spectra exhibit a and c dipole selection rules; transitions of the normal species and several of the isotopically substituted species occur as tunneling doublets. The complex has a stacked structure with Cs symmetry; the C2H4 and SO2 moieties both straddle the mirror plane with the C2 axis of SO2 crossed at 90 ° to the carbon–carbon bond axis (i.e., only the S atom lies in the symmetry plane). The distance between the centers of mass (Rcm) of C2H4 and SO2 is 3.504(1) A and the deviation of their planes from perpendicular to Rcm is 21(2) ° and 12(2) °, respectively. The tunneling splittings arise from a rotation of the ethylene subunit in its molecular plane. The barrier to internal rotation is 30(2) cm−1. The dipole moment of the complex is 1.650(3)D. The deuterium nuclear quadrupole coupling constants for C2H3D⋅SO2 are χaa=−0.119(1...

Fragmentative and stereochemical isomerization probes for homolytic carbon to phosphorus bond scission catalyzed by bacterial carbon-phosphorus lyase

Three bacterial strains, Agrobacterium radiobacter, Klebsiella oxytoca, and Kluyvera ascorbata, isolated by enrichment culture for carbon to phosphorus bond cleavage ability, were analyzed for the mode of C-P bond fission. The cleavage of alkyl phosphonic acids to alkanes and inorganic phosphates proceeded both aerobically and anaerobically, and growth on trideuteromethylphosphonic acid yielded trideuteromethane as product. These data indicate that functionalization of the organic moiety does not precede carbon to phosphorus bond cleavage. As probes for radical intermediates, cyclopropylmethylphosphonic acid and cis-1,2-dideutero-1-propenylphosphonic acid were used in growth experiments and the gaseous hydrocarbon products were examined. With the cyclopropylmethylphosphonic acid probe, all three bacteria produced methylcyclopropane, but only K. oxytoca and K. ascorbata also generated the acyclic olefin I-butene, and then only in very low quantity (0.6 and 0.3% versus methylcyclopropane, respectively). With the propenylphosphonic acid probe, cis-1,Zdideuteropropene was formed with greater than 98% retention of configuration with each bacterial strain. Only for K. oxytoca was the alternate product, in this case trans-1,2dideuteropropene, clearly detected at 1.5%. Thus, C-P bond fission may yield radical intermediates that are trapped efficiently at the enzyme active site or, alternatively, homolysis of the C-P bond may occur as a minor reaction pathway.

The benzene-SO2 and pyridine-SO2 complexes

Abstract The benzene-SO 2 and pyridine-SO 2 complexes have been observed for the first time using Fourier transform microwave spectroscopy. The complexes have different geometries. In benzene-SO 2 , the two planar species are stacked one above the other. In pyridine-SO 2 , the pyridine plane rotates by 70°, so that it is more nearly perpendicular to the SO 2 plane.

The structures and dipole moments of Ar–PF3 and Kr–PF3

The complexes of PF3 with Ar and Kr, were studied by Fourier transform microwave spectroscopy. The force constants and amplitudes of vibration for the van der Waals modes of the complexes and the average moments of inertia and structural parameters were estimated from the centrifugal distortion constants. The distance (Rc.m. )ave between the rare‐gas atom and the center of mass of PF3 is 3.959 A for the Ar complex and 4.077 A for Kr while the angle (θc.m. )ave between the Rc.m. vector and the C3 axis of the PF3 is 69.30° and 67.25°, respectively. The dipole moments of both complexes and of free PF3 were determined. The induced dipole components estimated for the rare gas using electric fields from ab initio calculations of PF3 agree with the experimental values for a conformation with the rare gas over a PF2 face. The PF2 face conformation is also consistent with the observed and ab initio estimates of the 83 Kr nuclear quadrupole coupling constant for the 83 Kr–PF3 species.

The microwave spectrum and structure of krypton--phosphorus trifluoride

The rotational spectrum of the weak complex between krypton and phosphorus trifluoride has been observed using a Fourier transform microwave spectrometer with a pulsed supersonic nozzle molecular beam source. The complex is an asymmetric top._The distance r,, between the krypton atom and the center of mass of the PF, molecule is 4.0722 A and the angle between the r,, vector and the C, axis of the PF, is 68.25”. Based on the centrifugal distortion constant DJ and a pseudodiatomic model, the binding energy of the complex is estimated to be 218 cm-‘.

Microwave spectrum, molecular structure and dipole moment of pivalaldehyde

The microwave spectra of eight isotopic species of pivalaldehyde [(CH3)3CCHO] have been studied in the frequency region 9–40 GHz. The zero-point average skeletal structure has been derived to be: r[C(1)O]= 1.206(6)A, r[C(1)–H]= 1.130(5)A, r[C(1)–C(2)]= 1.516(7)A, r[C(2)–C(3)]=r[C(2)–C(4),(5)]= 1.537(2)A, ∠ C(1)C(2)C(3)= 110.5(4)°, ∠ C(1)C(2)C(4),(5)= 107.4(3)°, proj.∠ C(4),(5)C(2)C(1)= 120.78(4)°, ∠ CCO = 126.0(5)° and ∠ CCH(1)= 113.0(3)°. The tert-butyl group is found to be tilted 2° away from the CO bond. Accurate Stark effect measurements have been performed on the main species, (CH3)3CCDO and (CD3)3CCHO. The ground-state dipole moment of (CH3)3CCHO was determined as µa= 2.618(5) D and µb= 0.728(2) D giving µtotal= 2.717(5) D at an angle of 13.6° to the CO bond.

The microwave spectrum and structure of the neon-phosphorus trifluoride complex

Abstract Symmetric top spectra were observed for the 20Ne·PF3 and 22Ne·PF3 van der Waals dimers using a Fourier-transform microwave spectrometer. The center-of-mass distance between Ne and PF3 is 3.373(3) A. The experimental data, in conjunction with the van der Waals radii of the atoms and with ab initio calculations, are consistent with the neon atom on the symmetry axis over the F3 face of the PF3. Normal mode analysis of the van der Waals vibrations based on the centrifugal distortion constants yields force constants fR = 0.00647 mdyn A−1 and fΘ = 0.00464 mdyn A for the 20Ne·PF3 isotopic species.

Cis and Gauche Propanal: Microwave Spectra and Molecular Structures

The microwave spectra of twelve isotopic species of cis propanal (CH3CH2CHO) and six isotopic forms of the less stable gauche rotamer have been studied to determine accurate structural parameters for both conformers. The following bond lengths (Å) and angles (°) were derived: