Apparent twist angle

The value of the apparent twist angle in the LC cell is lower than the one set by the preferred azimuthal director alignment on the substrates (shown in Figure 3.12... 

Figure 3.12 The value of the apparent twist angle in the LC cell Atp is lower than the angle set by the preferred azimuthal director alignment on the substrates (shown by solid and dashed lines respectively), because the strong azimuthal anchoring substrate affects the director aligmnent on the weak azimuthal anchoring one [34]. Reproduced from V.P. Vorflusev, H.S. Kitzerow, and V.G. Chigiinov, Azimuthal surface gliding of liquid crystals. Applied Physics Letters 70, 3359 (1997), American Institute of Physics...

In 1992, McLendon and coworkers reported results of a study of another series of porphyrin dyads with zinc in one porphyrin and iron in the second. These were related in structure to dyad 3, but the number of phenyl linkers varied from one to three. These workers found an apparent value for y in Eq. 2 of 0.4 A . They explained this result by a theory that attributes the drop in rate constant not to increased distance, but rather to the decrease in conjugation between the porphyrins that occurs at each phenyl ring junction due to the biphenyl twist angle of - 50°. Each phenyl ring results in a drop in rate of approximately six-fold [32]. 

Maps of the values of the unit twist ( / ) and unit height (ft) as a function of the torsion angles 0i and 02, are reported for generic isotactic [s(M/N) symmetry] and syndiotactic [s(M/N)2 symmetry] vinyl polymers in Figures 2.5 and 2.6, respectively. It is apparent that only one set of symmetry-related curves corresponds to any given value of the unit twist / (different from 180°) for the isotactic polymer, while there are two such sets for the syndiotactic polymers.27... 

Bond angles and lengths for 3-bromoflavone have been determined <82AX(B)983>. Whilst the two rings of the chromone system are essentially coplanar, the 2-phenyl group is twisted by 45.9° relative to the rest of the molecule apparently the steric interaction between the bromine atom at C-3 and H-2 outweighs the resonance stabilization which would be associated with a completely planar structure. 

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