The phase transition in crystalline octamethylcyclotetrasiloxane is due to transition of the molecules from Ci to S4 symmetry. During melting, a further change in the structure of the molecule occurs; in the liquid phase it apparently possesses C4 symmetry, which is also preserved in the gas phase.
The transformations of the molecule [OSi(CH3)2]4 consist of a change in the conformation of ring and do not lead to any significant change in the bond lengths and valence angles in the ring. A vital role in the mechanism of the molecular rearrangement is played by the lability of the SiOSi angle-thermal excitation of the nonplanar deformational vibrations of the siloxane ring.
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The authors would like to express their profound gratitude to V. N. Nikitin and L. I. Maklakov, for providing the possibility of using the DFS-12 instrument and a cryostatic cuvette for the Raman spectra, to D. S. Nedzvetskii, who aided in obtaining the spectra on the ISP-67 instrument, and to V. P. Davydova, who provided the octamethylcyclotetrasiloxane.
Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1168–1177, July, 1964
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Lazarev, A.N., Tenisheva, T.F. Polymorphism of molecules and complex ions in oxygen compounds of silicon and phosphorus. Communication 4. Phase transitions and conformations of the octamethylcyclotetrasiloxane molecule [OSi(CH3)2]4 . Russ Chem Bull 13, 1086–1094 (1964). https://doi.org/10.1007/BF00863106
- Phase Transition
- Liquid Phase