Chirality, origin

In most common chiral molecules, chirality arises from chiral tetravalent atoms. A conformation-independent chirality code (CICC) was developed that encodes the molecular chirality originating from a chiral tetravalent atom [42], For more generality, a conformation-dependent chirality code (CDCC) is used [43]. CDCC ti cats a molecule as a rigid set of points (atoms) linked by bonds, and it accounts for chirality generated by chirality centers, chirality axes, or chirality planes. 

There are two different kinds of sources of molecular chirality central chirality and axial chirality (Fig. 1). Central chirality is due to the existence of chiral carbon, whereas axial chirality originates from twisted structures of molecules, between which a sufficiently high energy barrier exists, preventing the chiral conformational interconversion in ambient conditions. Surprisingly, however, the introduction of nonchiral molecules to chiral liquid crystalline environments sometimes enhances the chirality of the systems [3-5]. This means that inherently nonchiral molecules act as chiral molecules in chiral environments. This occurs in the following way. Molecules with axial chirality behave as nonchiral molecules when the potential barrier is low enough for chiral conformational interconversion. But when such... 

Terms such as macroscopic, nanoscopic, and mesoscopic chirality originate from studies by Mislow (A. B. Buda, T. Auf der Heyde, K. Mislow, Angew. Chem. 1992, 104, 1012-1031 Angew. Chem. Int. Ed. 1992, 31, 989-1007) and Avnir (O. Katze-nelson, H.Z. Hel-Or, D. Avnir, Chem. 

Does the way by which chirality originated tell us anything about life s origin It is noteworthy that several routes exist that led to the formation of chiral compounds. 

The e bis-adducts 45 (Scheme 7-8) and ent-AS (not shown) provide examples for optically active fullerene derivatives in which the chirality originates only from the optically active tether, and the intensities of their CD bands (Ae values < 30 cm mmol" ) are smaller than those of ( C)-2 and i A)-2 (Scheme 7-11) with inherently chiral functionalization patterns [25]. 

Goldanskii, V. I. Semenov, N. N. (1992) Chirality, Origin of Life and Evolution. In J. K. TrSn Thanh Van ct.al. (eds.). Frontiers of Life, Editions Frontiers, Gif-sur-Yvette Cedex, France, pp. 67-85. 

Maikov et al. reported on the synthesis of chiral 2,2 -bip) idine N-monoxide and N,N -dioxide derivatives whose chirality originated from a terpene unit. 

The word chirality originates from Greek (hand). Chiral objects (and... 

Fajszi, Cs. Czege, J. (1981). Critical evaluation of mathematical models for the amplification of chirality. Origin of Life, 11, 143-62. 

A particular case in this category is that of atropisomeric compounds (those where chirality originates from a barrier to rotation over a single bond). In a thermal reaction, racemization occurs unless the temperature is sufficiently low. The peculiar temperature independence of photochemical reactions allows to transform axis chirality into point chirality with no loss. 

This reaction was utilized to synthesize (-)-a-thujone (Scheme 55)3 The two centers of chirality in the cyclopropane ring were controlled in a highly diastereoselective manner by the center of chirality originally present in the starting aldehyde 176. 

Keywords Amplification of ee Asymmetric autocatalysis Automultiplication Chiral discrimination Circularly polarized light Quartz Isotope chirality Origin of chirality Pyrimidyl alkanol Spontaneous absolute asymmetric synthesis... 

Carbon-isotope chirality is experimentally difficult to discriminate because the chirality originates from the very small difference between the carbon-12 and carbon-13. Therefore, it has been a question whether isotopically substituted carbon chiral compounds can induce chirality in some enantioselective reactions. To address this problem, we performed asymmetric autocatalysis triggered by a chiral compound arising solely from carbon-isotope substitution. 

The thiazolidinyl analogue 202 of pseudouridine, and its enantiomer, have been made, with chirality originating in d- or L-cysteine, ° whilst thiazolidinones 203 (B=Cyt, Thy, 5-fluoro-Cyt) have been prepared, using Pummerer-type chemistry. 4 -Azathymidine derivatives such as 204 have been prepared by cycloadditions of nitrones with vinyl acetate, followed by base- sugar condensation, and the isoxazolidinyl nucleoside 205, and its trans-isomer, have been made as racemates. The N-in-ring analogue 206 of 3 -deoxythymidine has... 

There is a third problem for which chirality information is of current interest anisotropic phases are often stabilized by chiral structures. Apart from chiral structures with enantiomorphic crystals of chiral compounds, suprastructural chirality exists in liquid crystal phases built up by chiral molecules as in the cholesteric phases and the smectic C phases. Even liquid crystalline phases with suprastructural chirality originating in achiral, so-called banana-shaped molecules, seem to be possible. Anisotropic polymer films with chiral structures have been found. It can be anticipated that chiroptical spectroscopy with anisotropic chiral systems will lead to new questions and answers. 

What is the common origin Physicists say that chirality occurs because of the tilting of molecules to the layers, but chemists tend to argue the other way around molecules become tilted in smectic phases because they are chiral. We then proposed that the chiral origin is due to the spiral conformation of molecule, according to two following points. 

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