Super achiral

Achiral (separation of diastereomeric derivatives) and chiral (sepa-ration of enantiomers) chromatography gas chromatography high-performance liquid chromatography super- and sub-critical fluid chromatography thin-layer chromatography... 

It was emphasized that, in comparison to the short-lived and weak interact tions in isotropic solution, more intimate and long-lived interactions are expected to occur between a chiral inductor and an achiral, as well as chiral, substrate leading to an enhanced enantio- or diastereoselectivity in confined zeolite super cages. v ... 

Enantiomeric compounds in which the asymmetric center is a tetravalent carbon, as in Fig. 2, represent the largest class of chiral molecules. The tetrahedral orientation of the bonds to a tetravalent carbon is such that when four nonidentical ligands are present, the mirror image of the molecule is nonsuperimposable, and the molecule is enantiomeric and chiral. When two of the ligands are identical, the mirror image is super-imposable, and the molecule possesses a plane of symmetry and is achiral. 

The best combination of chiral ligands and activators can easily be found out in an efficient way by super high throughput screening (SHTS) employing CO-HPLC with achiral stationary phase for affording the most enantioselective activated catalyst to give excellent yields and enantioselectivities. 

Structures VII and VIII are identical because rotating either one 180° in the plane of the paper makes it super-imposable with the other one. VII possesses a symmetry plane and is achiral. Achiral stereoisomers which have chiral centers are called meso. The meso structure is a diastereomer of either of the enantiomers. The meso structure with two chiral sites always has the (RS) configuration. 

Achiral molecule (Sections 5.3 and 5.4) A molecule that is super-posable on its mirror image. Achiral molecules lack handedness and are incapable of existing as a pair of enantiomers. 

The history of optical isomerism goes back to the year 1815, when the phenomenon was discovered by the French physicist Jean-Baptist Biot [1]. Optical activity was defined as the ability of a substance to rotate the plane of polarisation of light. Some years later, his student, Louis Pasteur [2] proposed that this optical activity of certain organic compounds was a consequence of their molecular asymmetry, that produces non-super-imposable mirror-image structures. A molecule which is not super-imposable on its mirror image is said to be chiral Conversely, a molecule which is superimposable on its mirror image is described as achiral... 

Every object has a mirror image. Many objects are achiral. By this we mean that the object and its mirror image are identical, that is, the object and its mirror image are super-posable one on the other. Superposable means that one can, in one s mind s eye, place one object on the other so that all parts of each coincide. Simple geometrical objects such as a sphere or a cube are achiral. So is an object like a water glass. 

Why is one of the stereoisomer of the tartaric acids optically inactive The structures labeled (2R,3S) and (2S,3R) have two equivalent chiral carbon atoms, and each structure has a plane of symmetry. We recall from Section 8.2 that a structure with a plane of symmetry is achiral, and that it is super-imposable on its mirror image. In the case of achiral tartaric acid, the plane of symmetry is between C-2 and C-3, so the top half of the molecule is the mirror image of the bottom half... 

Bronsted acid as well as metal Lewis acids catalyze many usual organic reactions aldol reaction, esterification, acetal formation and so on. Even if we took achiral Br0nsted acid as the topic of this chapter, it would not be possible to discuss everything. Therefore, we focus on the recent developments of achiral super Br0nsted acids , especially their design and application to organic reactions [2]. 

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