The molecular structure of difluoroisocyanato silane: A combined microwave spectral and theoretical study

Guirgis, Gamil A.; Wang, Zichao; Lirjoni, Jonel; Palmer, Michael H.; Obenchain, Daniel A.; Peebles, Rebecca A.; Peebles, Sean A.

doi:10.1016/j.molstruc.2010.07.044

Cited by 6 publications

(32 citation statements)

References 40 publications

(69 reference statements)

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“…The NMR spectra of 1-isocyano-1-silacyclopent-3-ene (II) product are as expected; 1 H NMR showed a multiplet at δ 1.565 ppm, and singlets at δ 4.94 and 5.91 ppm. The 13 C NMR spectrum has bands at δ 16.80, 122.92, and 130.05 ppm.…”

Section: Synthesis and Spectral Details For 1-isocyano-1-silacyclopen...supporting

confidence: 65%

“…Our previous studies − on silyl isocyanates have shown the necessity for use of all-electron basis sets, which are triple zeta in the valence shell exponents; in addition, two or more sets of polarization functions are necessary. This was applied here, where we used the largest of the Pople et al − series of bases, denoted as 6-311++G(3df,3pd), for all atomic centers.…”

Section: Theoretical Methodsmentioning

confidence: 99%

“…Recently, we reported combined microwave spectral (MW) and theoretical studies of some silyl isocyanates where unusual structural features, such as wide SiNC angles, occur. − A similar study of cyclopropylsilyl isocyanate (C 3 H 5 –SiH 2 –NCO) by MW methods showed the presence of cis and gauche conformers, which have extremely wide CNSi angles of 156.2 and 153.0°, respectively. The cis structure (Figure ,I) shows that the classical isocyanato group lies almost above the center of the ring.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Structure of 1-Isocyano-1-silacyclopent-3-ene: A Combined Microwave Spectral and Theoretical Study

et al. 2019

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The microwave spectrum of 1-isocyano-1-silacyclopent-3-ene has been obtained from broad-band chirped-pulse Fourier transform microwave spectroscopy. The rotational constants (RCs) for the standard abundant isotopic species are A = 3328.4182(23), B = 1017.69404(53), and C = 1012.33297(58) MHz. The symmetric quartic centrifugal distortion constants, using the Ir representation in CS symmetry for ΔJ,ΔJK, ΔK, and δJ, have been evaluated; similarly, the 14N nuclear quadrupole coupling has been determined. Several singly substituted isotopologues observed in natural abundance enabled most of the heavy atom substructure to be determined. The five-membered ring is close to planar, but the orientation of the isocyanate unit, derived from the N13CO spectrum, unexpectedly lies above the ring center in a cis C2,5–Si–NC conformation. Our initial equilibrium structural searches led to a trans orientation of the C2,5–Si–NC unit, i.e., bending away from the ring. When the cis conformation was applied, the final equilibrium structure, assuming CS symmetry, gave RC values of 3221.3 (A), 1037.0 (B), and 1031.3 (C) MHz, very close to the MW values. This enabled the full-equilibrium structure to be determined with confidence. The principal bond lengths were 1.7157 (Si–N), 1.8696 (Si–C), 1.1998 (NC), and 1.1737 (CO) Å, with angles 163.3 (Si–NC), 178.1 (NCO), 96.5 (C–Si–C), and 118.7° (C–CC), respectively. The extensive widening of the SiNC angle is particularly notable; the SiNCO unit has a trans dihedral angle. The cis orientation implies a (weak) attractive force between the ring and isocyanate groups by a through-space interaction. An atoms in molecule study, where the local minima of electron density are determined, fails to disclose the exact nature of the interaction; however, a highly polarized skeleton was obtained. A systematic theoretical study of the Si–NC angle potential energy surface (PES) relative to the ring gave a very shallow double minimum with the barrier being less than 1 cm–1; a polynomial fit to the surface shows major contributions of both harmonic and quartic components. A similar study of the XSiN angle, where X is at the ring center, also gave a PES with considerable quartic character.

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Section: Synthesis and Spectral Details For 1-isocyano-1-silacyclopen...supporting

confidence: 65%

Section: Theoretical Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular Structure of 1-Isocyano-1-silacyclopent-3-ene: A Combined Microwave Spectral and Theoretical Study

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“…Despite broader lineshapes, and a resolution of $80 kHz resulting from the FFT parameters used on the oscilloscope, comparisons of frequency measurements between the CP-FTMW and resonant cavity instrument agreed to well within 6 kHz and the precision of the spectral fits (Tables 2-4) was also comparable to that typically obtained using the Balle-Flygare instrument. Subsequent studies using this CP-FTMW instrument have clearly resolved Br and 14 N nuclear quadrupole hyperfine structure in 1-bromobutane, 2-bromobutane [17] and difluorosilylisocyanate [18].…”

Section: Rotational Spectramentioning

confidence: 99%

Rotational spectrum of three conformers of 3,3-difluoropentane: Construction of a 480MHz bandwidth chirped-pulse Fourier-transform microwave spectrometer

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et al. 2010

Journal of Molecular Spectroscopy

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“…The electronic structures of 4a,b , including electric field gradients (EFGs) and derived 14 N nuclear quadrupole coupling constants (NQCCs), were determined using the Gaussian 09 (G-09) and MOLPRO suites; RHF and B3LYP single configuration calculations used G-09, while multiconfiguration SCF, coupled cluster with singles, doubles, and selected triples (CCSD(T)) calculations used MOLPRO. We used the largest Pople-style basis (6-311G++ (3pd, 3df)), which was previously successful, − for the equilibrium structures of molecules 1 – 3 . Subsequently, when conformational energy surface issues were studied at the lower level of MP2, we used the aug-cc-pVTZ basis set (H[4s3p2d], C,N,O,F[5s4p3d2f], Si[6s5p3d2f]), , which allows additional flexibility in the wave function.…”

Section: Theoretical Studymentioning

confidence: 99%

Molecular Structure of Cyclopropyl (Isocyanato) Silane: A Combined Microwave Spectral and Theoretical Study

et al. 2015

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The molecular equilibrium structures of two conformers (cis and gauche) of C3H5-SiH2-NCO have been deduced by a combination of microwave (MW) spectra at natural abundance including data from (13)C and (29,30)Si isotopomers and ab initio calculations. The MW rotational constants (RCs) for the most abundant isotopes are cis: A = 4216.3617(64), B = 1225.76654(91), and C = 1037.31468(77) MHz and gauche: A = 4955.55(79), B = 1094.9276(81), and C = 942.7031(80) MHz. The symmetric quartic centrifugal distortion constants have been evaluated for the cis conformer, using the I(r) representation for CS symmetry. Only partial substitution structures (PSSs) could be derived from the spectra after inclusion of the above isotopic combinations at each center. Using the PSSs, the full structures were determined by ab initio calculation of the equilibrium structures using coupled-cluster singles and doubles with selected triples configuration calculations (CCSD(T)); the two conformers have an energy difference of 228 cm(-1) (cis lower than gauche). The similarity of the calculated and MW RC results confirms the identities of the two compounds. The more interesting cis conformer has bond lengths C2-Si3, 1.9072(73), C2-C9 1.464(22), and C9-C10 1.4944(33) Å and angles Si3-C2-C10 119.4(12)° and C9-C2-C10 57.1(12)°, with similar results for the gauche conformer. The Si3N4C5 angle is wide in the cis conformer (145°) and nearly linear in the gauche conformer (179°). New physical insights into the bonding of cis conformers of this type have led the identification of an attractive force between the relatively crowded cyclopropyl and isocyanato groups in the cis conformation. This is demonstrated by three methods: Comparing electronic charges (both AIMALL and Mulliken analyses) in the pair of conformers shows a relative shift of density between these groups in the cis compound. Comparison of the highest occupied molecular orbitals (HOMOs) shows major mixing of density, exemplified by HOMO-1 in these structural units for the cis conformer but which is absent for the gauche conformer. Finally, the nearly linear isocyanate moiety (and the molecular dipole moment) of the cis conformer points closely toward the connected C atom of the cyclopropyl ring, while the gauche conformer dipole moment is significantly different in direction and points toward the midpoint of the C2Si3 bond. Both the HCSiN torsional and Si-N═C bending surfaces connecting these conformers were explored at the Møller-Plesset second-order perturbation theory level (MP2), which led to the exclusion of other conformers. The bending surface shows a very high amount of quartic potential function.

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The molecular structure of difluoroisocyanato silane: A combined microwave spectral and theoretical study

Cited by 6 publications

References 40 publications

Molecular Structure of 1-Isocyano-1-silacyclopent-3-ene: A Combined Microwave Spectral and Theoretical Study

Molecular Structure of 1-Isocyano-1-silacyclopent-3-ene: A Combined Microwave Spectral and Theoretical Study

Rotational spectrum of three conformers of 3,3-difluoropentane: Construction of a 480MHz bandwidth chirped-pulse Fourier-transform microwave spectrometer

Molecular Structure of Cyclopropyl (Isocyanato) Silane: A Combined Microwave Spectral and Theoretical Study

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