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Notes: The microwave spectra of 11 chemically different isotopic species of ethylphosphine (CH3CH2PH2) including all 13C and D single substituted species were recorded and assigned for the vibrational ground state. The b- and c-type transitions of the gauche conformers with symmetrically substituted ethyl groups and a PH2 group were found to be split due to tunneling between the equivalent forms. The spectra of these molecules were fit to a Hamiltonian containing Coriolis interaction terms. All other spectra were fit to asymmetric rotors with quartic centrifugal distortion. Complete rs structures were obtained for both the trans and gauche conformations. The r0 structures were derived from 45 and 48 rotational constants for the trans and gauche forms, respectively. Significant differences in the structures were found with the most notable one in the CCP angle which changes from 110.5° in the gauche form to 116° in the trans conformer. The methyl group in the gauche conformation is rotated away from a position symmetric with respect to the heavy atom plane. The structural differences are attributed to nonbonded repulsive interactions between the methyl and phosphino hydrogen atoms.

Notes: The microwave spectra in the region from 18.5 to 39.0 GHz have been measured and assigned for the following isotopic species of trifluoromethyl silane: CF328SiH3, CF329SiH3, CF330SiH3, CF328SiD3, CF329SiD3, CF330SiD3, CF328SiDH2, CF329SiDH2, CF328SiD2H, and CF329SiD2H. In addition to the vibrational ground state, two torsionally excited states were assigned for some of the asymmetrically substituted molecules whereas as many as thirteen states involving multiple excitation of the torsional and/or CF3 rocking modes were assigned for some of the symmetric rotor species. From a least squares adjustment to fit 18 rotational constants for the vibrational ground state, the following r0 structural parameters were obtained: r(C–F) =1.3600±0.0029 A(ring), r(C–Si)=1.8997±0.0071 A(ring), r(Si–H)=1.4600±0.0007 A(ring), r(Si–H) =1.4600±0.0007 A(ring), CSiH=107.15±0.03°, and FCSi=113.28±0.30°. The rs structural parameters were obtained for the SiH3 moiety and were found to be r(Si–H) =1.4598±0.0033 A(ring) and CSiH=107.17±0.09°. The dipole moment was obtained from the ground state Stark effect measurements on CF328SiDH2 and was found to be ||μa||=2.32±0.02 D. The barrier to internal rotation is estimated from relative intensity measurements to be 403±20 cm−1 (1.15±0.06 kcal/mol). These results are compared to the corresponding parameters of some similar molecules.

Notes: A continuous flow system has been used to measure the microwave spectrum (26.5 to 40.0 GHz) of rapidly decomposing N–bromodifluoromethanimine, CF2=NBr. The hyperfine structure of the spectrum caused by two nuclei with nuclear quadrupole moments (14N,79Br, or 81Br) has been analyzed and rotational, centrifugal distortion, and quadrupole coupling constants have been determined by a global least-squares fit for both bromine isotopic species. Identification and assignment of R transitions in the b-type spectrum have been facilitated considerably by the determination of the magnitude of the rotational constants from the hyperfine structure of the Q transitions alone. A structure compatible with the observed rotational constants has been determined for this planar molecule.

Notes: The microwave spectra of three isotopic Ge species of germyl azide, GeH3N3, have been assigned. The splittings due to internal rotation of the germyl group have been analyzed yielding a threefold barrier of 86.6(1) cm−1. An electric dipole moment of 2.58(2) D has been determined from the Stark effect. The following refined structural parameters have been obtained with a fixed and slightly bent azide group: r(GeN)=1.866(12) A(ring), r(GeH)=1.497(8) A(ring), α(GeNN)=115.9(14)°, α(HGeH)=112.2(10)° and a tilt of the symmetric germyl group of 4.0° away from the azide group.

Notes: The infrared and Raman (3500–30 cm−1) spectra of gaseous and solid propenoyl bromide, CH2 CHCBrO, have been recorded. The Raman spectrum of the liquid has been obtained and qualitative depolarization values have been measured. The fundamental asymmetric torsion for both the s-trans and s-cis conformers has been observed along with several hot transitions. From these transitions the potential function governing the internal rotation has been determined and the s-trans to s-cis barrier is 1861 cm−1 (5.32 kcal/mol), the trans conformer being more stable by 158±20 cm−1 (452±57 cal/mol). All normal modes have been assigned for the s-trans conformer and many of those for the s-cis conformer, based on band contours, depolarization values, and group frequencies. A normal coordinate calculation has been carried out by utilizing a modified valence force field to calculate the frequencies and the potential energy distribution for both conformers. Temperature studies of the Raman spectra of gaseous propenoyl fluoride and chloride and of the liquid phases of propenoyl chloride and bromide have been used to obtain the enthalpy differences between the s-trans and s-cis conformers for these compounds. For the bromide and chloride the s-trans conformer is clearly the more stable form but the data are inconclusive for the fluoride. Complete equilibrium geometries have been determined for both rotamers of the fluorideand chloride by ab initio Hartree–Fock gradient calculations employing both 3-21G and 6-31G* basis sets. The structural parameters are compared to those suggested from microwave and/or electron diffraction studies of these molecules. Both calculations are consistent with the s-trans conformation being thermodynamically preferred for the fluoride molecule and the s-cis conformation for the chloride, which is contrary to the experimental data for the chloride. The 3-21G basis set was used to obtain the ab initio force constants and frequencies for the s-trans and s-cis conformers of both the fluoride and chloride with fixed scaling, variable scaling, and without scaling factors. These results required several reassignments of fundamentals for both conformers of both molecules. Improved vibrational data for both the fluoride and chloride were very valuable for the reassignments. These results are compared with the corresponding quantities for some similar molecules.

Notes: The microwave spectrum of chlorocyclopentane has been reinvestigated. The ground state and two vibrationally excited states of the equatorial conformation of c-C5H935Cl have been identified. The ground state rotational constants are A=6424.51(14) MHz, B=1832.304(6) MHz, C=1523.163(5) MHz. The spectrum of the 37Cl substituted species has also been assigned. For the previously reported axial conformer of c-C5H935Cl, additional transitions have been measured in the ground state and the first excited state of the lowest frequency motion and the spectrum of another vibrationally excited state has been assigned. The experimental rotational constants have been used to derive plausible molecular structures for both conformers. The experimental quadrupole coupling constants are compatible with the proposed structures.

Notes: The microwave spectrum of a common decomposition product of CF2=NCl and CF2=NBr has been analyzed. The observed hyperfine structure requires the presence of 14N and the absence of Cl and Br in the molecule. The inertial defect establishes the planarity of the molecule. The observed rotational constants are A=11 464.024(4), B=11 151.892(4), and C=5643.146(4) MHz, which are very similar to those reported for CF2=O. The molecule is identified to be difluoromethanimine, CF2=NH. The dipole moment components were determined from the Stark effect to be |μa|=0.415(1), |μb|=1.330(1), and |μt|=1.393(1) D. The 14N quadrupole coupling constants are χaa=1.029(20), χbb=−2.560(17), and χcc =1.531(22) MHz. These data are compared to similar quantities for some corresponding molecules.

Notes: The high resolution (0.10 cm−1) far infrared spectra of gaseous acetone-d0, -d3, and -d6 were measured between 370 and 40 cm−1. The region of the methyl torsional transitions below 130 cm−1 was analyzed in terms of the semirigid rotor model for molecules with two internal C3v rotors and the two-dimensional torsional potential functions were determined. Effective barriers of 291 cm−1 (832 cal/mol) and sine–sine interaction terms of −l08 cm−1 (−309 cal/mol) were found for all three isotopic species. The results are compared with those from ab initio calculations and from the analysis of splittings in the microwave spectrum.

Notes: The microwave spectrum of ethyldifluorophosphine, CH3CH2PF2, has been investigated in the region from 18.0 to 39.5 GHz. The spectra of two conformers have been identified. The ground state and seven vibrationally excited states have been assigned for the more stable gauche conformer (phosphorus lone pair with respect to CH3 group), whereas the ground state and one excited state have been assigned for the trans form. Rotational and most quartic centrifugal distortion constants have been determined with A=6784.501(3), B=2930.156(2), C=2352.576(2) MHz for gauche and A=5444.910(3), B=3290.133(3), C=2871.915(3) MHz for trans, both in the ground state. Electric dipole moments were obtained from ground state Stark effect measurements: || μa||=1.990(4), || μb||=0.855(4), || μc||=0.091(7), || μt||=2.168(2) D for gauche and || μa||=1.780(10), || μb||=0, || μc||=1.077(10), || μt||=2.081(10) D for trans. Using a new computer program, a diagnostic least-squares fit of the structural parameters suggests significant structural differences between the conformers, notably the C–C–P angle which changes from 110.7° in the gauche form to 114.9° in the trans form. From a temperature study of the microwave spectrum, it was found that the gauche conformer is at least 80 cm−1 (229 cal/mol) more stable than the trans conformer. These results are compared to similar quantities in some corresponding molecules.