18306-73-5Relevant academic research and scientific papers
Synthesis and thermal stability of silicon-containing esters of phosphorus acids 5.* the relative migration ability of substituents at the silicon atom in the thermal rearrangement of trialkylsilylmethyl diphenyl phosphates
Zakharov,Molchanova,Shcherbina,Petrovskii,Kabachnik
, p. 1718 - 1724 (1998)
A number of trialkylsilylmethyl diphenyl phosphates MeRR'SiCH2OP(O)(OPh)2 (Ia-e: R = Et (a), Pr (b), CF3CH2CH2 (c, e), Me3SiCH2 (d); R' = Me (a-d), Et (e)) were synthesized and their thermal rearrangement, of the 1,2-shift type, was studied. The rearrangement consists of the migration of an alkyl group from Si atom to the methylene carbon atom and gives the corresponding silyl esters. The rate of the rearrangement was found to increase in the order 1d 3CH2CH2 3SiCH2, which differs substantially from the order in which the rate of the rearrangement of phosphates 1a-d changes. The electro-negativity of the migrating group affects noticeably the relative ability to migrate.
Polar Order and Symmetry Breaking at the Boundary between Bent-Core and Rodlike Molecular Forms: When 4-Cyanoresorcinol Meets the Carbosilane End Group
Westphal, Eduard,Gallardo, Hugo,Caramori, Giovanni Finoto,Sebastián, Nerea,Tamba, Maria-Gabriela,Eremin, Alexey,Kawauchi, Susumu,Prehm, Marko,Tschierske, Carsten
supporting information, p. 8181 - 8197 (2016/06/14)
Two isomeric achiral bent-core liquid crystals involving a 4-cyanoresorcinol core and containing a carbosilane unit as nanosegregating segment were synthesized and were shown to form ferroelectric liquid-crystalline phases. Inversion of the direction of one of the COO groups in these molecules leads to a distinct distribution of the electrostatic potential along the surface of the molecule and to a strong change of the molecular dipole moments. Thus, a distinct degree of segregation of the carbosilane units and consequent modification of the phase structure and coherence length of polar order result. For the compound with larger dipole moment (CN1) segregation of the carbosilane units is suppressed, and this compound forms paraelectric SmA and SmC phases; polar order is only achieved after transition to a new LC phase, namely, the ferroelectric leaning phase (SmCLsPS) with the unique feature that tilt direction and polar direction coincide. The isomeric compound CN2 with a smaller dipole moment forms separate layers of the carbosilane groups and shows a randomized polar SmA phase (SmAPAR) and ferroelectric polydomain SmCsPSphases with orthogonal combination of tilt and polar direction and much higher polarizations. Thus, surprisingly, the compound with the smaller molecular dipole moment shows increased polar order in the LC phases. Besides ferroelectricity, mirror-symmetry breaking with formation of a conglomerate of macroscopic chiral domains was observed in one of the SmC phases of CN1. These investigations contribute to the general understanding of the development of polar order and chirality in soft matter. The power of an ester group: Reversing one COO group in a bent-core mesogen leads to very different dipole moments, gives rise to distinct segregation of the carbosilane end groups from the aliphatic and aromatic segments, and thus modifies the mode of self-assembly, the coherence length of polar order, and the capability of mirror-symmetry breaking. One of the isomers forms a new leaning-type liquid-crystalline (LC) phase in which the tilt coincides with the polar direction, whereas the other forms a ferroelectric LC in which the tilt is perpendicular to the polar direction (see figure).
