Chirality motion dependence

Time reversal, mentioned above in connection with PT-enantiomers, is also at the heart of a distinction between time-dependent and time-independent enantiomorphism. In a series of publications,33-36 Laurence Barron has provided the basis for his argument that The only compelling reason for generalizing Kelvin s definition is to encompass absolute asymmetric synthesis and the concept of chirality in elementary particle physics by including motion-dependent chirality. 37 According to Barron33 ... 

In summary, objects that exhibit enantiomorphism, whether T-invariant or not, belong to chiral groups. Hence, motion-dependent chirality is encompassed in the group-theoretical equivalent of Kelvin s definition. 

The stereospecificity of vibrational optical activity, on the other hand, arises from the fact that the vibrations take place in a chiral framework and VOA intensities depend in large part on the extent and phasing of coupling or mixing of vibrational motion in different parts of the molecule. In addition, many local symmetry restrictions are lifted in chiral molecules, for example, the local de-... 

More detailed kinetic information about the motions and reactions of the alkyl/aryloxy radical pairs can be obtained if the alkyl carbon atom making an ether bond is chiral and the alkyl aryl ether is optically active. Because the radical centers of the alkyl fragments derived from irradiation of such ethers are either planar or invert very rapidly, they exist initially with their aryloxy partners as prochiral pairs. Their ability to retain the memory of the chirality of their parent ethers and impart it to the rearrangement products depends on the ratio between the in-cage rates of radical tumbling and radical pair combination. 

The idea that the vacuum represents an achiral interface that separates two space-time segments of opposite chirality developed from the notion that mass-dependent quantum effects arise from a field in the vacuum which affects the smallest of objects most prominently. The original argument (Boeyens, 1992) was that quantum behaviour results from feeble interactions through the interface, which create the impression of random wave-like perturbations imposed on the regular motion of small particles. 

The efficiency of such a DKR-based synthesis depends on the kinetic parameters of the parallel reaction [kg and kj) and racemization (kj ). This is determined not only by the structural parameters of the catalyst and substrate, but also by the conditions that facilitate or enforce in situ racemization of the chiral substrate. In this review, examples of DKR have been classified into five categories according to the method of racemization (i) tautomerization, (ii) internal motion (pyramidal inversion, and deformation and rotation), (iii) elimination-addition and addition-elimination, (iv) nucleophilic substitution and (v) others. Representative equilibrium for each type of racemization is shown in Figure 5.2. 

In the chlorination of the fi-CD complex, the optical yields of 4 and 7 increase about three times on lowering the temperature from 25 to — 20°C. Judging from the result that the chiral induction and reactivity for the gas-solid chlorination of styrene included in -CD depends on the temperature, the motion of the guest molecule within the host molecule should be restricted by decreasing temperature. This result, however, is different from that of the gas-solid chlorination of ( )-cinnamic acid in the fi-CD cavity, where the optical yields of products were nearly Constant over the temperature range —25 to 50 °C as reported previously [9]. 

Molecular dynamics studies in chiral smectic liquid-crystalline phases by solid-state NMR measurements have been reported. The temperature dependence of the spin-lattice relaxation time Ti was investigated. For the aliphatic carbons in a flexible chain the value of Ti was found to increase with increasing temperature, because the molecular motion characterised by Xc was faster than the Larmor frequency coq-... 

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