Pseudoasymmetry: A final twist?

Chandrasekhar, Sosale
The original definition of "pseudoasymmetry" conveyed the apparent paradox that a tetrahedral center with four different groups did not result in overall chirality. However, there are problems in applying the concept to cyclic systems that do not contain chirotopic centers. Pseudoasymmetry appears most appropriate to acyclic systems with chirotopic carbon centers, e.g. the meso trihydroxyglutalic acids. Analogous cyclic cases, e.g. the isomeric 1,4-dimethylcyclobutanes, are best treated as diastereomers, and may indeed be described by an interesting extension of the like-unlike notation. Remarkably, in several tri- and tetramethylcyclohexanes, CIP descriptors cannot be applied even to chirotopic centers, which can only be described by the modified 1-u notation.


Molecular homochirality and the parity-violating energy difference. A critique with new proposals
Chandrasekhar, Sosale (Wiley, 2008-02-01)
Previous proposals for the origin of molecular homochirality, based on the effect of the weak neutral current (W-NC) on enantiomers, and the amplification of the resultant parity-violating energy difference (PVED), are possibly flawed. The additive amplification of PVED in crystals and polymers ("Yamagata hypothesis") cannot lead to detectable levels of optical activity, the original theory apparently overestimating PVED by a factor equal to Avogadro's number. An alternative theory based on the irreversible...
Raman bandwidths calculated for the librational ( a -phase) and internal (8, d loc and d phases) modes in solid N 2 using pseudospin-phonon coupling (PS) and energy-fluctuation (EF) models
Yurtseven, Hasan Hamit (Elsevier BV, 2020-10-01)
This study gives the calculation of the Raman bandwidths using the models of the pseudospin-phonon coupling (PS) and energy fluctuation (EF) where the Raman frequency calculated from the molecular field theory, is considered as the order parameter close to the phase transitions in nitrogen. In particular, we study the temperature dependence of the Raman bandwidths and frequency shifts of the Eg librational mode (zero pressure) and the internal modes of and (at various pressures) for the solid nitrogen by ...
Common Secondary and Tertiary Structural Features of Aptamer-Ligand Interaction Shared by RNA Aptamers with Different Primary Sequences
İlgü, Müslüm; Khounlo, Ryan M.; Lamm, Monica H.; Nilsen-Hamilton, Marit (MDPI AG, 2019-12-01)
Aptamer selection can yield many oligonucleotides with different sequences and affinities for the target molecule. Here, we have combined computational and experimental approaches to understand if aptamers with different sequences but the same molecular target share structural and dynamical features. NEO1A, with a known NMR-solved structure, displays a flexible loop that interacts differently with individual aminoglycosides, its ligand affinities and specificities are responsive to ionic strength, and it po...
Asymmetric synthesis of norbornene based 1,4-Aminoalcohol derivatives and applications in asymmetric diethylzinc reactions
Erdem, Mine; Tanyeli, Cihangir; Department of Chemistry (2007)
The asymmetric synthesis of chiral norbornene based 1,4-aminoalcohols and their applications in asymmetric diethylzinc addition reactions was perfomed starting from meso-anhydride 50. The desymmetrization of this meso-anhydride 50 was done by the usage of quinine or quinidine cinchona alkaloids with very high enantiomeric excess values (up to 98% ee) and chemical yields. The Quinidine-mediated desymmetrization of meso-anhydride 50 with methanol gave (2R,3S)-(+)-cis-monoester 51. The amination of this result...
Spectroscopic intensities as measures of order parameter close to order-disorder transitions
Yurtseven, Hasan Hamit (Springer Science and Business Media LLC, 1988-01-01)
The infrared and Raman intensities can be related to the order parameter close to order-disorder phase transitions in crystal systems. In the present study this relationship has been obtained and compared with our experimental results for ammonium halides. Our predictions give satisfactory agreement with the observations in these crystals. It is proposed that the FTIR techniques can be appropriately used to evaluating the order parameter in various crystal systems.
Citation Formats
S. Chandrasekhar, “Pseudoasymmetry: A final twist?,” CHIRALITY, pp. 771–774, 2008, Accessed: 00, 2020. [Online]. Available: