Chirality diastereomers

Intramolecular hydrogen bonding is present in the chiral diastereomer of 225 5 tetra methylhexane 3 4 diol but absent in the meso diastereomer Construct molecular models of each and suggest a reason for the difference between the two... 

Scheme 6.13 gives some examples of Cope and oxy-Cope rearrangements. Entry 1 shows a reaction that was done to compare the energy of chair and boat TSs. The chiral diastereomer shown can react through a chair TS and has a AG about 8 kcal/mol lower than the meso isomer, which must react through a boat TS. The equilibrium is biased toward product by the fact that the double bonds in the product are more highly substituted, and therefore more stable, than those in the reactant. 

The R,S system is quite general and has many advantages (and a few disadvantages) compared with the d,l notation for simple molecules. For diastereomers, it provides much clearer notations than meso, erythro,1 and threo1 that have been used for many years to designate the configurations of achiral and chiral diastereomers having two chiral carbon atoms ... 

Careful examination of these mirror images shows that they are, in fact, identical. If the (25,37 )-stereoisomer is rotated 180° in the plane of the paper, the structure on the right is produced and it is identical to the (27 ,350-stereoisomer on the left. Because the compound is superimposable on its mirror image, it is not chiral and does not rotate plane-polarized light. Another way to determine that this compound is not chiral is to note that it has a plane of symmetry that bisects the C-2—C-3 bond. Compounds such as this one, which contain chirality centers but are not chiral are called weso-stereoisomers. me.vo-Tartaric acid is human-made and does not occur in nature. Overall, then, tartaric acid has only three stereoisomers the two enantiomers of the chiral diastereomer (often called the d,/-diastereomer) and the weso-diastereomer. 

A stereocenter is an atom at which the interchange of two groups gives a stereoisomer. Stereocenters include both chirality centers and double-bonded carbons giving rise to cis-trans isomers. For example, the isomers of but-2-ene are achiral and they contain stereocenters (circled), so they would meet this definition. They have no chiral diastereomers, however, so they are not correctly called meso. 

The original definition of meso is an achiral compound that has chiral diastereomers. Our working definition of meso is an achiral compound that has chirality centers (usually asymmetric carbon atoms). The working definition is much easier to apply, because we don t have to envision all possible chiral diastereomers of the compound. Still, the working definition is not quite as complete as the original definition. 

Based on residues Y that can pass the annulus99 but not each other, two chiral diastereomers are possible for 47 namely a / -symmetrical derivative (RRR/SSS) and a C2-symmetrical derivative (RRS/SSR). While the D3-symmetrical hexa-methylether was isolated (in low yield and impure form) by Yamato et al.,97 all our... 

Diaatereoniera are stereoisomers that are not mirror images of each other Chiral diastereomers have opposite oonfiguralioits at some (one or more) chirality centers, but have the same configuration at others. Enantiomers. by contrast, have opposite configurations at oU chirality centers. A full descriptMHi of the four threonine stereoisomers is given in Table 9.2-... 

Unfortunately, attempts to separate P-chiral diastereomers of complex 52 by column chromatography were unsuccessful due to its instability to moisture, so the stereochemical experiment could not be performed. That goal has been... 

In both cases, a nucleophile will come in across the unsaturated side of the molecule. The two chiral centres at the bridgeheads of the chiral molecule 85 have nothing to do with this. The only consequence of the chiral centres will be that the product will be a chiral diastereomer whereas (with the achiral ketone 86) the product will be an achiral diastereomer. 

Reactions of enantiotopic faces "e" are either afacioselective (ql) or nonfacioselective with achiral reagents (ql0,qll,ql2,ql5,ql6,ql7,ql8), but stereofacioselective (enantiofacioselective) with chiral reagents (q23,q24,q27,q37,q38,q41). With only enantio-facioselectivity at work, and no role for vectoselectivity - e.g. with C2-symmetric reagents - one would expect two chiral diastereomers (q23). With non-C2-symmetric reagents, vectoselectivity would come into play, and more complex mixtures may result (vide infra). Here, enantiofacioselectivity refers to the face type in the reactant substrate. 

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