Chiral distortion

Metal salen complexes can adopt non-planar conformations as a result of the conformations of the ethane-1,2-diyl bridge. The conformations may have Cs or C2 symmetry, but the mixtures are racemic. Replacement of the ethylenediamine linker by chiral 1,2-diamines leads to chiral distortions and a C2 chiral symmetry of the complex due to the half-chair conformation of the 5-membered ring of the chelate. Depending on substitution at the axial positions of the salen complex, the symmetry may be reduced to Q, but as we have seen before in diphosphine complexes of rhodium (Chapter 4) and bisindenyl complexes of Group 4 metals (Chapter 10) substitution at either side leads to the same chiral complex. Figure 14.10 sketches the view from above the complex and a front view. 

Fig.24 Hierarchical homochiral self-assembly as observed via STM on Au(lll) Chirally distorted rubrene (a) self-assembles in a first step into homochiral pentagons and these, in a second step, into homochiral rings containing 50 monomers, (b) [59], Within these pentacontamers, all ten pentamers are rotated equally 12° with respect to the virtual spokes of the wheel (c). Reprinted with permission from Wiley...

Both experimental data73,75 and theoretical calculations78 show that differences in the sign of the Cotton effects of 5-mono- and 5,5-disubstituted barbiturates are sensitive to chiral distortions within the barbituric acid ring. The induced CD spectra of barbiturates as inclusion complexes with / -cyclodextrin support the foregoing conclusion.79... 

Vanin et al. studied order proflles of the perdeuterated laurate chain in chiral and achiral phases by means of deuterium NMR. The quadrupole splittings measured for the sequence of CD2 moieties are all quite similar for the nematic and chiral nematic phase the conclusion was that chiral distortions of the micellar shape must be very small. Their proposal for the mechanism behind the phase chirality is analogous to the one for polypeptides an asymmetric point charge distribution which in this case was speculated to be created by the chiral dopant on the micellar surface [19]. Radley and Tracey prepared samples from a racemic detergent and observed high fluidity, whereas those consisting of some enantiomeric excess showed a significantly increased viscosity [30]. But this is no proof for the association of micelles to necklaces. 

Whoever reads this volume without rejecting the picture of a point electron that only shows up as a probability distribution has the same problem. In our perception it occurs, like other elementary entities, as a persistent, flexible, wave-like, chiral distortion of space-time. It has mass, charge and spin by virtue of a characteristic wave structure. It disperses into the vacuum on interaction with another of opposite chirality. 

Table 2. Calculated energy gap due to an in-plane Kekul distortion for CNTs having chiral vector L/a = (m, 2m). The critical magnetic flux (p. and the corresponding magnetic field are also shown. The coupling constant is A, = 1.62.

The functionalization of zinc porphyrin complexes has been studied with respect to the variation in properties. The structure and photophysics of octafluorotetraphenylporphyrin zinc complexes were studied.762 Octabromoporphyrin zinc complexes have been synthesized and the effects on the 11 NMR and redox potential of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraarylporphyrin were observed.763 The chiral nonplanar porphyrin zinc 3,7,8,12,13,17,18-heptabromo-2-(2-methoxyphenyl)-5,10,15,20-tetraphenylporphyrin was synthesized and characterized.764 X-ray structures for cation radical zinc 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin and the iodinated product that results from reaction with iodine and silver(I) have been reported.765 Molecular mechanics calculations, X-ray structures, and resonance Raman spectroscopy compared the distortion due to zinc and other metal incorporation into meso dialkyl-substituted porphyrins. Zinc disfavors ruffling over doming with the total amount of nonplanar distortion reduced relative to smaller metals.766 Resonance Raman spectroscopy has also been used to study the lowest-energy triplet state of zinc tetraphenylporphyrin.767... 

Among the numerous nickel dithiophosphates, the chiral complexes deserve to be cited.41 Unusual trinuclear Pd3(p3-E)2[S2P(OR)2]2(PPh3)2 with E = S, Se, R = Et, Pr, Pr, Bu, have been prepared and Pd3(p3-S)2[S2P(OEt)2]2(PPh3)2 revealed a structure containing three distorted square-planar Pd atoms and sharing two p3-S ligands.42... 

A distorted conjugated pair of double bonds is an intrinsically chiral chromophoric system, and its overall chiroptical properties depend on the reduced symmetry of the chromophore itself as well as on the perturbing action of a dissymmetric environment. 

---