Microwave, r0 structural parameters, conformational stability and vibrational assignment of cyclopropylcyanosilane

Durig, J. R.; Guirgis, Gamil A.; Sawant, D. K.; Seifert, Nathan A.; Deodhar, Bhushan S.; Pate, Brooks H.; Panikar, Savitha S.; Groner, P.; Overby, Jason S.; Askarian, Sahand M.

doi:10.1016/j.chemphys.2014.10.004

Cited by 4 publications

(6 citation statements)

References 32 publications

(53 reference statements)

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“…The present approach can clearly be used much more widely and, in particular, may well offer an explanation for some of the related cyclopropylsilanes C 3 H 5 SiH 2 X. In the case where X = CN, which also exists as a mixture of cis and gauche conformers, 4−6 there is the possibility of overlap of the CN unit with the ring but by a sideways approach, as shown in Figure 2 of Durig et al 4 However, the similar behavior of the cases where X = SiH 3 or CF 3 must involve other properties because the polarities of these substituents are opposite. The similarity of these two groups lies in the local CH 3 and CF 3 group MOs of a 1 symmetry which will project backward toward the C 3 H 5 ring across space in the cis conformer.…”

Section: Discussionmentioning

confidence: 70%

“…Only the N–E term favors the cis conformer, which represents an electron attraction between the atomic groups, part of which is between the C 3 H 5 to NCO units, via the SiH 2 unit. This same reasoning would apply to the earlier known cyclopropylsilanes C 3 H 5 SiH 2 X, where X = H, CN, CF 3 , which also exist as cis and gauche conformers, − but this was not explored.…”

Section: Structural Results and Discussionmentioning

confidence: 99%

“…The nuclear (N–N) repulsion energies and 2-electron (E–E repulsion) energies both favor the gauche conformer, but this is outweighed by the electron–nuclear (E–N) attraction energy, which favors the more compact cis, and this must be a result of overall attraction of the isocyanato and cyclopropyl groups. Durig et al have reviewed the cis/gauche conformer stabilities for several related cyclopropanes. The present example with cis lower than gauche is similar to that for cyclopropyl (cyano) silane (123 ± 13 cm –1 ); the reverse order of stability occurs with cyanomethylcyclopropane, C 3 H 5 CH 2 CN, where the gauche is more stable, showing that even replacing SiH 2 by CH 2 can have a major difference.…”

Section: Discussionmentioning

confidence: 99%

“…The full molecular structures were determined by ab initio calculations, which showed that internal rotation of the silyl isocyanato and cyclopropyl groups leads to interconversion of these with a low barrier. The experimental presence of the more congested cis conformer suggests attraction between the NCO and C 3 H 5 units, and this led to a more detailed theoretical analysis than the previous studies of three related cyclopropylsilanes (C 3 H 5 SiH 2 X, with X = H, CN, CF 3 ), which also exist as cis and gauche conformers. − …”

Section: Introductionmentioning

confidence: 98%

“…The experimental presence of the more congested cis conformer suggests attraction between the NCO and C 3 H 5 units, and this led to a more detailed theoretical analysis than the previous studies of three related cyclopropylsilanes (C 3 H 5 SiH 2 X, with X = H, CN, CF 3 ), which also exist as cis and gauche conformers. 4…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 70%