Enantiomers organic molecules

Optical purity The percentage of optical activity observed relative to that of the pure enantiomer. Organic molecules Carbon compounds (traditionally excepting CO2 and compounds where carbon enters... 

In the early days following the discovery of chirality it was thought that only molecules of the type CWXYZ, multiply substituted methanes, were important in this respect and it was said that a molecule with an asymmetric carbon atom forms enantiomers. Nowadays, this definition is totally inadequate, for two reasons. The first is that the existence of enantiomers is not confined to molecules with a central carbon atom (it is not even confined to organic molecules), and the second is that, knowing what we do about the various possible elements of symmetry, the phrase asymmetric carbon atom has no real meaning. 

The most common cause of chirality is the presence of four different substituents bonded to a tetrahedral atom, but that atom doesn t necessarily have to be carbon. Nitrogen, phosphorus, and sulfur are all commonly encountered in organic molecules, and all can be chirality centers. We know, for instance, that trivalent nitrogen is tetrahedral, with its lone pair of electrons acting as the fourth "substituent" (Section 1.10). Is trivalent nitrogen chiral Does a compound such as ethylmethylamine exist as a pair of enantiomers ... 

Chirality is an important aspect of aroma chemicals since enantiomers of the same compound may possess different organoleptic characters. Chirality means the occurrence of one or more asymmetric carbon atoms in an organic molecule. Such molecules exhibit optical activity and therefore have the ability to rotate plane-polarised light by equal amounts but in opposite directions. In other words, two stereoisomers which are mirror images of each other are said to be enantiomers. If two enantiomers exist in equal proportions, then the compound is called racemic. Enantiomers can be laevorotatory (, I, -, S), meaning rotating the plane of the polarised light to the left or dextrorotatory (°, d, -f, R), that is. 

Molecular imprinting is a special polymerization technique making use of molecular recognition [18] consisting in the formation ofa cross-linked polymer around an organic molecule which serves as a template. An imprinted active site capable of binding is created after removal of the template. This process can be applied to create effective chromatographic stationary phases for enantiomers separation. An example of such a sensor is presented in Section 6.3.2.3. 

Like other phenomena involving interactions between electromagnetic radiation and organic molecules, as in infrared, ultraviolet, and nmr spectroscopy, optical rotatory dispersion curves often are quite sensitive to small changes in structure. As an example, the rotatory dispersion curves for enantiomers of cis- and trcMr-lO-methyl-2-decalones, 16 and 17, are reproduced in Figure 19-7 ... 

Quartz can be chiral. A study by Bernal et al. (44) showed that quartz may have played a role as an adsorptive substrate which served as a template in the abiotic evolution of biopolymers. Additionally, it has been reported that the stereospecific adsorption of various organic molecules such as vitamin B12 and d,l camphor can occur on quartz. Moreover, it is also possible to separate the two enantiomers by adsorption onto powdered d or 1 quartz (45). 

Photoenantiomerization of different classes of organic molecules was investigated. However, the expectation that if a pure enantiomer can be racemized by light then photoderacemization of the racemate with cpl should lead to an optically active photostationary state, does not hold in all cases. Even when enantiomerization is fast, the Ae values are often too small. Molecules like 6 and 7 were extensively studied by Schuster and his group (e.g., [52,53]) in search of a molecule suited for an optical switch for mesogenic phase transitions. 

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