The molecular structure and curious motions in 1,1-difluorosilacyclopent-3-ene and silacyclopent-3-ene as determined by microwave spectroscopy and quantum chemical calculations

McFadden, Thomas M. C.; Moon, Nicole; Marshall, F. E.; Duerden, Amanda; Ocola, Esther J.; Laane, Jaan; Guirgis, Gamil A.; Grubbs, Smitty

doi:10.1039/d1cp04286f

Cited by 6 publications

(3 citation statements)

References 38 publications

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“…This is confirmed from the experimental structure with the exception that some atoms, particularly the silicon, are very near the b and c axis, both complicating the accuracy of the Kraitchman coordinate position and giving larger errors in those coordinates. This proximity and large uncertainty in the dihedral angle is very similar to that observed in 1,1-difluorosilacyclopent-3-ene, which had doubling in some transitions possibly due to an unidentified motion. No such doubling was observed in these spectra, however, which led the authors to conclude that the large uncertainty in any dihedral angle is just due to the uncertainty in the coordinate positions as the determined values, ignoring the errors, are very close to the theoretical structures.…”

Section: Resultsmentioning

confidence: 99%

“…For this, the authors are not entirely sure because there was no additional splitting observed in either spectrum to provide a case for some form of large amplitude motion. It has been observed by the authors previously in similar systems that curious motions can exist in these silicon ring molecules, but there was no direct evidence here. This could be due to the frequency range of the experiment and warrants further study, but it was outside the capabilities available to the authors.…”

Section: Discussionmentioning

confidence: 99%

“…In recent years, the authors have undertaken rotational spectroscopy studies that investigate the structural differences in substituting a carbon with a silicon atom. − Studies of these systems have led to interesting physiochemical results like ring-puckering motions, planar vs nonplanar ring structures, or C 2 symmetry in straight-chain alkane species where one may expect C 2 v . In some of these systems, the potential energy surfaces of the ring-puckering motion may be flatter at the base through the puckering coordinate than the carbon analogues or may result in a double well.…”

Section: Introductionmentioning

confidence: 99%

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Rotational Spectrum and Ring Structures of Silacyclohex-2-ene and 1,1-Difluorosilacyclohex-2-ene

Moon,

Duerden,

McFadden

et al. 2023

J. Phys. Chem. A

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Silacyclohex-2-ene and 1,1-difluorosilacyclohex-2-ene have been synthesized, and the chirped-pulse, Fourier-transform microwave spectra of each have been observed and analyzed from 4.9 to 23.1 GHz. Quantum chemical calculations have been performed at the B3LYP-D3BJ/Def2TZVP level of theory and predict μ a to be the largest dipole moment component with a significantly larger value in this component for 1,1-difluorosilacyclohex-2-ene. In accordance with this prediction, the spectra were predominantly a-type with the observation of a few b-and c-type transitions. The signalto-noise ratio was adequate in both spectra to observe 29 Si, 30 Si, and all singly substituted 13 C isotopologues in natural abundance. All spectra have been fit to a semirigid rotational Hamiltonian and are presented. Analysis of the physical meaning of the fitted parameters is explored and determined to hold for the rotational constants while being more empirical for the centrifugal distortion terms. Experimental structures of both molecules indicate that the quantum chemically calculated structures for the atoms in the ring are a very close depiction of the experimentally determined structures. The structures of each molecule are compared to similar molecules for context, where it is shown that both molecules possess a similar "half-chair" conformation to that of the all-carbon analogue, cyclohexene.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%