Abstract:A detailed analysis of the vibrational spectra of 1,3-disilacyclobutane and 1,3-disilacyclobutane-l,1,3,3-d4 in vapor, liquid, and solid phases shows that the molecules have puckered ring conformations in the former two phases but become planar in the solid state. This is reflected by the frequency shifts of the ring deformation and SiH2 (or SiD2) rocking modes which are uncoupled for the planar conformation but interact strongly for the puckered structure. Frequency differences between gas and solid phases fo… Show more
“…For the characterization of organosilanes it is important to know the vibrational frequencies expected for the six modes associated with each SiX 2 group. Table compares the data from the present work for the silacyclobutanes (SCB) to those of 1,3-disilacyclobutanes (DSCB) , and 3-silacyclopentene (3SCP) . As can be seen, the functional group frequency associated with each type of vibration is in a narrow range for the Si−H and Si−D stretches but covers a broader wavenumber range for the lower frequency vibrations.…”
Ab initio calculations have been carried out for silacyclobutane (SCB) and its 1,1-difluoro and 1,1-dichloro derivatives in order to compute the structures and dihedral angles of puckering for these molecules. For SCB the calculated dihedral angle of 35° agrees nicely with the 36° value obtained from far-infrared work. The calculated angles of 29° and 31° for the fluoro and chloro derivatives, respectively, can be compared to electron diffraction results of 25° and 26°. The zero-point-corrected barriers calculated using the MP2/cc-pVTZ level of theory were 523 (as compared to 440 cm−1 experimental), 186, and 433 cm−1 for SCB and its fluoro and chloro derivatives, respectively. Calculated structural changes in the dihalo derivatives can be ascribed to the high electronegativity of the halogen atoms. High-level DFT computations were also carried out in order to calculate the infrared and Raman spectra of these three molecules as well as the SCB 1,1-d
2 isotopomer. The agreement between experimental and calculated spectra is remarkably good for all four molecules. The predicted frequencies and intensities were utilized to reassign several of the weaker spectral bands and also to characterize the 1130 cm−1 signature band present in the infrared spectra of all silacyclobutanes. This arises from the α-CH2 in-phase wagging vibration, which is very much affected by the neighboring silicon atom. The DFT calculations also demonstrated that two of the wagging and twisting motions of the CH2 group next to the silicon atom have frequencies much lower than in typical organic molecules. This work also provides frequency ranges that can be expected for the six vibrations of SiX2 groups (X = H, D, F, Cl) in organosilanes.
“…For the characterization of organosilanes it is important to know the vibrational frequencies expected for the six modes associated with each SiX 2 group. Table compares the data from the present work for the silacyclobutanes (SCB) to those of 1,3-disilacyclobutanes (DSCB) , and 3-silacyclopentene (3SCP) . As can be seen, the functional group frequency associated with each type of vibration is in a narrow range for the Si−H and Si−D stretches but covers a broader wavenumber range for the lower frequency vibrations.…”
Ab initio calculations have been carried out for silacyclobutane (SCB) and its 1,1-difluoro and 1,1-dichloro derivatives in order to compute the structures and dihedral angles of puckering for these molecules. For SCB the calculated dihedral angle of 35° agrees nicely with the 36° value obtained from far-infrared work. The calculated angles of 29° and 31° for the fluoro and chloro derivatives, respectively, can be compared to electron diffraction results of 25° and 26°. The zero-point-corrected barriers calculated using the MP2/cc-pVTZ level of theory were 523 (as compared to 440 cm−1 experimental), 186, and 433 cm−1 for SCB and its fluoro and chloro derivatives, respectively. Calculated structural changes in the dihalo derivatives can be ascribed to the high electronegativity of the halogen atoms. High-level DFT computations were also carried out in order to calculate the infrared and Raman spectra of these three molecules as well as the SCB 1,1-d
2 isotopomer. The agreement between experimental and calculated spectra is remarkably good for all four molecules. The predicted frequencies and intensities were utilized to reassign several of the weaker spectral bands and also to characterize the 1130 cm−1 signature band present in the infrared spectra of all silacyclobutanes. This arises from the α-CH2 in-phase wagging vibration, which is very much affected by the neighboring silicon atom. The DFT calculations also demonstrated that two of the wagging and twisting motions of the CH2 group next to the silicon atom have frequencies much lower than in typical organic molecules. This work also provides frequency ranges that can be expected for the six vibrations of SiX2 groups (X = H, D, F, Cl) in organosilanes.
“…Mixtures of the un-cross-linked and cross-linked forms of polymer 5a were prepared in Nujol and were used for IR analysis. The IR spectra showed that the intensity of the sharp peak at 930 cm -1 , which was assigned to the wagging mode of the CH 2 on the DSCB rings, decreased gradually as the curing reaction proceeded and that a broad peak is formed at 1050 cm -1 , which is assigned to the stretching mode for the bridging CH 2 group in the SiCH 2 Si open-chain structure (Figure ). ,, 5 IR spectra of polymer 5a in Nujol: (A) uncured, (B) cured at 220 °C for 2 h, (C) cured at 240 °C for 4 h, and (D) cured at 280 °C for 8 h.…”
Cyclolinear carbosilane polymers with disilacyclobutane (DSCB) rings in the main-chain
structure were prepared by means of acyclic diene metathesis (ADMET) polymerization of the corresponding 1,3-dibutenyl-1,3-disilacyclobutanes. The copolymerization of a monomer of this type with a
noncyclic organosilane diene allowed for the incorporation of a varying number of DSCB rings into the
polymer backbone. Subsequent hydrogenation of the double bonds with p-toluenesulfonhydrazide resulted
in a saturated hydrocarbon structure in the main chain without affecting the DSCB ring. All of the
resultant polymers are well-defined materials with DSCB rings incorporated into the backbone structure,
as evidenced by NMR spectroscopy and GPC analyses. The thermal behavior of these polymers was
characterized by DSC and TGA. DSC indicated low T
gs, and TGA evidenced high thermal stability in an
inert atmosphere. In addition, large exothermic peaks were observed in the DSC, which indicated, along
with the IR and solid-state 29Si NMR spectra, that cross-linking occurs during heating to ca. 250 °C via
opening of the imbedded DSCB rings. The swelling properties of the resultant, thermally stable,
carbosilane network materials on exposure to various solvents were also examined.
“…The additional strain imposed on the five-membered ring by substitution of CH2 by C=0 favors the planar ring in this case and 0 is reduced. The epimers thujone and isothujone, both of which are bicyclic monoterpenes derived from 98 by substituting isopropyl and methyl at the 1 and 4 positions, respectively, have been shown418 to have ring conformations similar to that of 98. On the other hand, when a double bond is placed in the five-membered ring of 93 to give bicyclo[3.1.0]hex-2-ene (99), the two endocyclic trigonal carbon atoms now hold the ring essentially planar417 (see Table XVIII).…”
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