Examples of chiral in the following topics:
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- Stereogenic elements may be chiral or achiral.
- First, try to identify all chiral stereogenic centers.
- Formulas having one chiral center are always chiral; and if two or more chiral centers are present in a given structure it is likely to be chiral, but in special cases, to be discussed later, may be achiral.
- The chiral centers will be identified by red dots.
- Compounds C, D & H have more than one chiral center, and are also chiral.
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- All objects may be classified with respect to a property we call chirality (from the Greek cheir meaning hand).
- A chiral object is not identical in all respects (i.e. superimposable) with its mirror image.
- Chiral objects have a "handedness", for example, golf clubs, scissors, shoes and a corkscrew.
- All dissymmetric objects are chiral.
- All asymmetric objects are chiral.
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- The enolate donor in an aldol reaction may also have a center of chirality, leading to the formation of additional diastereomeric products.
- The evidence indicates mediocre selectivity, probably resulting from steric differences between large and small substituents (RL and RS) at the chiral center.
- These Z-enolates are expected to favor 1,2-syn diastereoselectivity of the newly created α & β chiral centers, as noted earlier.
- Excellent facial selectivity is found in reactions of these nucleophiles Here the 1,2-diastereoselectivity of the newly created α & β chiral centers is strongly anti, as expected.
- From past observations, the 1,2-diastereoselectivity of the newly created α & β chiral centers is expected to exhibit moderate syn-diastereoselectivity.
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- Fischer projection formulas are particularly useful for comparing configurational isomers within a family of related chiral compounds, such as the carbohydrates.
- When describing acyclic compounds incorporating two or more chiral centers, many chemists prefer to write zig-zag line formulas for the primary carbon chain.
- These compounds are all chiral and only one enantiomer is drawn (the D-family member).
- In cases having two adjacent chiral centers, such as this, the prefixes erythro and threo may be used to designate the relative configuration of the centers.
- The syn-anti nomenclature may be applied to acyclic compounds having more than two chiral centers, as illustrated by the example in the colored box.
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- With the exception of the first three compounds (top row) these molecular structures are all chiral.
- When chiral compounds are found in nature they are usually enantiomerically pure, although different sources may yield different enantiomers.
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- As a general rule, a structure having n chiral centers will have 2n possible combinations of these centers.
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- Aldol reactions of prochiral donor and acceptor reactants produce racemic mixtures of chiral adducts.
- The chiral substituent may then be removed, yielding the final enantiomerically pure aldol adduct.
- A substituent serving this purpose is commonly called a chiral auxiliary.
- Chiral auxiliaries have been prepared from different kinds of natural products, including amino acids, alkaloids and terpenes.
- As a rule, Evans' chiral auxiliaries exert a controlling influence in reactions with chiral α-substituted aldehydes, overriding even Felkin-Ahn preferences.
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- Since the nitrogen in these compounds is bonded to three different groups, its configuration is chiral.
- If the nitrogen atom were the only chiral center in the molecule, a 50:50 (racemic) mixture of R and S configurations would exist at equilibrium.
- If other chiral centers are present, as in the ephedrin isomers, a mixture of diastereomers will result.
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- Simply put, any chiral species that are present are racemic.
- It is interesting to note that chiral conformations are present in most conformationally mobile compounds, even in the absence of any chiral centers.
- The gauche conformers of butane, for example, are chiral and are present in equal concentration in any sample of this hydrocarbon.
- The following illustration shows the enantiomeric relationship of these conformers, which are an example of a chiral axis rather than a chiral center.
- All chiral twisted conformers are present as racemates, so this compound cannot be resolved.
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- The 1,2- and 1,3-dichlorocyclohexanes each have two centers of chirality, bearing the same set of substituents.
- The cis & trans-1,4-dichlorocyclohexanes do not have any chiral centers, since the two ring groups on the substituted carbons are identical.
- The chair conformer of the cis 1,2-dichloro isomer is chiral.
- Since the cis isomer has two centers of chirality (asymmetric carbons) and is optically inactive, it is a meso-compound.
- The corresponding trans isomers also exist as rapidly interconverting chiral conformations.