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Reactants, molecules containing chiral

Molecules Containing Chiral Centers as Reactants or Products... [Pg.253]

Preparation of enantiomerically enriched materials by use of chiral catalysts is also based on differences in transition-state energies. While the reactant is part of a complex or intermediate containing a chiral catalyst, it is in a chiral environment. The intermediates and complexes containing each enantiomeric reactant and a homochiral catalyst are diastereomeric and differ in energy. This energy difference can then control selection between the stereoisomeric products of the reaction. If the reaction creates a new stereogenic center in the reactant molecule, there can be a preference for formation of one enantiomer over the other. [Pg.92]

In the enantioselective synthesis, the asymmetry (i.e., the stereoselectivity) is induced by the external chiral catalyst, while the diastereoselective synthesis does not require a chiral catalyst. The stereogenic center already present in the molecule is able to induce stereoselectivity, assuming that the synthesis starts with a single enantiomer. For instance, imagine that an a,/ -substituted product is formed, and that the reactant already contains a stereogenic carbon at a. If the reaction of (aS) leads, e.g., largely to (aS, / R) and hardly to the (aS, /IS) diastereomer (i.e., stereoisomers that are not mirror-images of each other), the reaction is diastereoselective (Scheme 14.2). [Pg.497]

Achieving efficient photochemical chiral induction within zeolite supercages requires a geometrical distribution of reactant and chiral inductor molecules in the same supercage (type V in Fig. 2). By restricting a photoreaction to a supercage that contains both a reactant and a chiral inductor, and by avoiding the reaction in the absence of the chiral inductor, efficient chiral induction should be achieved... [Pg.352]

Similarly, the two faces at a trigonal carbon in a molecule containing a chiral center are diastereotopic. Both chiral and achiral reactants can distinguish between these diastereotopic faces. Many examples of diastereoselective transformations of such compounds are known. One of the cases which has been examined closely is addition reactions at a trigonal center adjacent to a chiral carbon. Particular attention has been given to the case of nucleophilic addition to carbonyl centers. [Pg.106]

Artificial hydrothermal vents might be constructed and supplied with plausible concentrations of simple reactants such as CO, H2, NH3, and H2S. Appropriate levels of amino adds induding a small chiral excess, along with the sorts of amphiphilic molecules described above, can be rationalized by the findings from the Murchison meteorite. Organic molecules such as found in irradiated interstellar ice models, including HMT, can also be induded. The system should indude weathered feldspars, which can be modified to indude the reduced transition-metal minerals that they are known to contain. [134] Such minerals as Fe,Ni sulfides are likely to have been both present and stable in the environment of early Earth and are known [153, 155] to catalyze formation of organic molecules from simpler precursors. [Pg.201]

There are two ways by which a chiral auxiliary can be attached to a molecule of interest in order to insure that it crystallizes in a chiral space group—covalently and ionically. The covalent approach requires little explanation, typical examples being ester or amide formation between the achiral carboxylic-acid-containing photoreactant and an optically pure alcohol or amine. The ionic attachment is similarly straightforward, consisting of salt formation between the carboxylic-acid-containing reactant and an optically pure amine. In this case, the resulting chiral ammonium ion is referred to as an ionic chiral auxiliary. [Pg.466]

Solid-state asymmetric photoreactions are classified in Table 1. A chiral crystal is first needed as a reactant medium in solid-state photoreaction. Chiral compounds necessarily crystallize in a chiral space group. Hence the most reliable method of bringing about an asymmetric reaction is to utilize a chiral crystal containing covalently chiral molecules. However, this kind of chiral crystal of a chiral mole-... [Pg.486]


See other pages where Reactants, molecules containing chiral is mentioned: [Pg.607]    [Pg.352]    [Pg.574]    [Pg.574]    [Pg.185]    [Pg.113]    [Pg.167]    [Pg.609]    [Pg.955]    [Pg.71]    [Pg.957]    [Pg.86]    [Pg.374]    [Pg.78]    [Pg.2]    [Pg.93]   


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Chiral molecules

Chiral molecules chirality

Container molecule

Molecules Containing Chiral Centers as Reactants or Products

Reactant molecule

Reactants, molecules containing chiral centers

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