Conformational stability, r0 structural parameters, ab initio calculations, and vibrational assignment for silacyclopentane

Conformational stability, ab initio calculations and vibrational assignment for 1,1-difluoro- and 1,1-dichloro-1-silacyclopentane

“…The spectrum of the Raman liquid and solid displayed no significant change in the relative intensities of the bands as the temperature was decreased. This observation clearly indicates either that there is only one conformer present, or if more than one the enthalpy difference is near zero as previously reported by Guirgis et al [1]. The ab initio restricted Hartree Fock calculations support the presence of only one conformer.…”

“…Guirgis et al [1,3] reported that the 1-silacyclopentane and 1-germacyclopentane molecules exist in twisted form. The Laane [2] laboratory previously showed the molecule to be twisted with C 2 symmetry but based their assignments and force constant calculations on the easier to visualize planar C 2v model.…”

“…The conformational stabilities of these conformers are of interest to structural chemists and physicists. Recently the conformational stability of silacyclopentane [1,2] and germacyclopentane [3] was investigated, and the results indicate that these molecules are found to exist in the twist form. This finding is in agreement with the previously reported vibrational spectra and assigned on the basis of C 2v symmetry although the authors [2] pointed out that the molecule is C 2 symmetry.…”

Infrared and Raman spectra, conformational stability and vibrational assignment of 1-chloro-1-silacyclopentane

“…The ring breathing mode is predicted to be the strongest of these modes and is assigned at 859 cm −1 with a weaker band (29.5 km/mol) at 876 cm −1 which is one of the ring deformations (52% S 25 ). Two higher frequency ring deformations are expected based on their corresponding assignments for silacyclopentane [8] and they are assigned at 939 (32% S 23 ) and 1020 (47% S 22 ) cm −1 where 23 has major contributions from four other symmetry coordinates. Three other ring deformations are expected in the region from 700 to 400 cm −1 and two of them could readily be assigned at 483 (43% S 34 ) and 404 (58% S 35 ) cm −1 but the other one is difficult to assign although the band at 681 cm −1 (19% S 31 ) seems to be the best choice.…”

“…For example, we determined the conformational stability of silyl-and germylcyclopentane [8,9] and both of these molecules have only one stable conformer and it is the twisted conformer. We also re-investigated [10] the vibrational spectra of fluorocyclopentane where, from the initial infrared study, it was concluded that it was the same as the bromo-and chlorocyclopentane with axial and equatorial conformers [1].…”