Subject chiroptical properties

Relatively few applications of optically active tertiary arsines to asymmetric synthesis have been reported by comparison with the extensive work with phosphines . Authoritative accounts of the synthesis and stereochemistry of compounds of Group V elements are available other reviews cover the subject up until 1979 . For general treatments of organoarsenic chemistry up until 1976, including optically active compounds, two important works are available . Of related interest is an article on stereochemical aspects of phosphorus chemistry and another published in this series on optically active phosphines preparation, uses and chiroptical properties . On matters concerning the intricacies of resolutions work, the reader should consult Reference 21, especially Chapter 7, which is entitled Experimental Aspects and Art of Resolutions. 

Helical Poly(phenylacetylenes). The most widely studied helical-substituted polyacetylenes are based on poly(phenylacetylene) with chiral ring substituents. Pol5unerization of chiral phenylacetylenes was first reported in 1995 (72). 4-(-)-Menthoxycarbonylphenylacetylene (41) was subjected to the polymerization with several transition metal catalysts such as [(nbd)RhCl]2 and WCle. The resultant Rh-based polymer shows a large optical rotation and intense CD effects in the electric absorption region of the main chain. The polymer, thus, exists in a helical conformation with an excess of one-handed screw-sense. Poly(phenylacetylene) with small chiral pendants, poly(42), in contrast, displays poorer chiroptical properties. Interestingly, an increase in temperature steeply increases the optical rotation of poly(41) if the polymer is produced with a W catalyst. Such a drastic enhancement of chiroptical properties is not observed in the case of Rh-based poly(41). 

The interpretation of some reaction mechanisms, and of interrelations of chemical structures and chiroptical properties as well, are still subject to contradictory arguments. In this review in most cases we have reported the propositions of the authors and let the reader form his own opinion until future results decide. 

However, given a sufficiently strong steric effect, a permanent twist can be induced in a carbon-carbon double bond even without a push-pull effect. This is a field that has been the subject of much interest, as exemplified by the intense but still unsuccessful search for tetra-/m-butylethylene, and by the still very active studies of trans-cyclooctenes. Besides the synthetic challenge, such compounds present interesting chiroptical and other physical properties, and a knowledge of their heats of formation presents crucial tests for current force fields. 

The conformational structures of polysilane main chains at the macro-and microscopic levels are controllable by suitable choice of the side chain structures. Similarly, it is also the side chain which controls the optoelectronic properties by effecting the optical band gap. In the case of phenyl-substituted polysilanes, electronic interaction between the delocalized Si chain cr-bonding orbitals and the it-orbitals of the aryl groups causes a dramatic modification of both the band gap and conformational properties [61,83]. These aryl-containing polysilanes may be potential candidates for applications in a molecular-based chiroptical switch and memory in the UV/visible region. On the other hand, the precise control of helical polymers is now a subject of great interest and importance, due to the tech-... 

Chiral phosphorus-containing dendrimers which have ferrocene molecules at the periphery have been the subject of work by Majoral and co-workers. These materials will have obvious applications in catalysis. Layer-by-layer dendrimers, which are built up containing chiral ferrocenylphosphine molecules, have also been prepared, and their chiroptical and electrochemical properties have been investigated. A recent article covers the basic chemistry of ferrocene-containing liquid-crystalline polymers which stems from the extensive work of Deschenaux, who essentially pioneered the area. A ferrocene end-capped dendrimer has also been used in carbon monoxide sensing. The actual dendrimer, shown as 19, has 48 ferrocene molecules on the periphery. 

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