Enantiomers structure

Identical molecules (Both are the R enantiomers) Structural isomers (one is optically active, the other is not) Enantiomers (R and S optical isomers)... 

The transfer to the aldehyde is also stereospecific. The alcohol formed is the R enantiomer. The S enantiomer (structure 8.16), formed from CH3CDO and NADH, has a specific rotation of - 0.28 0.03°.7... 

For each set of examples, make a model of the first stmcture, and indicate the relationship of each of the other stmctures to the first structure. Examples of relationships same compound, enantiomer, structural isomer. 

We call two structures that are not identical, but are mirror images of each other (like these two) enantiomers. Structures that are not superimposable on their mirror image, and can therefore exist as two enantiomers, are called chiral. In this reaction, the cyanide ions are just as likely to attack the front face of the aldehyde as they are the back face, so we get a 50 50 mixture of the two enantiomers. 

Make sure that you are clear about this C and D are identical molecules, while A and B are mirror images of each other. Reflection in a mirror makes no difference to C or D they are superimposable upon their own mirror images, and therefore cannot exist as two enantiomers. Structures that are superimposable on their mirror images are called achiral. 

Enantiomers/Structural Isomers. The particular optical isomer of a drug being used in a formulation is quite important. For example, quinine is used to treat malaria quinidine, its optical isomer, is used for heart arrhythmia. In 1985, Ciurczak observed that although pure d- and L-amino adds gave identical spectra, the racemic mixtures (dl-) produced an entirely different spectra. Some work was presented by Ciurczak in 1986, which was later expanded and published by Buchanan et al. in 1988, where the enantiomer ratio was determined via NIR. 

D-d(CGCGCG) and L-d(CGCGCG), pair only with complementary strands which have the same chirality. Racemic DNA molecules only interact at the end of the strand to form crystals in which the D-configured double helix s ends stick to two L-configured double helices and vice versa In the crystal, a pseudohelix is thus formed which contains half-a-turn of right-handed and half-a-turn of left-handed enantiomer structures (Figure 5.33). There is no formation of polyphosphate sheets. 

Therefore, there are three stereoisomers. Isomers I and II are enantiomers, while isomers I and III are diastereomers. Note that isomer III has a plane of symmetry, therefore it has no enantiomers. Structure III is called a meso compound. 

There are two stereocenters (C-2 and C-3) and a total of four stereoisomers. The four stereoisomers are organized into two pairs of enantiomers—structures I and II are one pair and III and IV are another pair. A new term, diastereomer, is used to indicate the relationship of either compound in one pair with either compound in the other pair. Neither structure I nor structure II is superimposable or the mirror image of structure III or structure IV. 

There are two stereocenters for 2,3-dichlorobutane but there are only three stereoisomers. There is a pair of enantiomers (I and II). Unlike the situation with 2,3-dichloropentane, structures III and IV are not a pair of enantiomers. Structures III and IV are superimposable by rotating either one 180° in the plane of the paper. This occurs because the two stereocenters (C-2 and C-3) have the same set of four different substituents (H,C1,CH3, CHCl — CH3). A correct answer for this problem must show either the equal sign between structures III and IV or only one structure from III and IV. The lone compound, whether shown as III or IV, is referred to as a rrteso compound. The meso compound has a plane of symmetry (symbolized by a dotted line in the structure shown below). The meso compound is achiral and optically inactive even though it possesses two stereocenters. 

Stereoisomeric 2,3-butanediols shown in their eclipsed conformations for convenience. Stereoisomers (a) and ib) are enantiomers. Structure (c) is a diastereomer of (a) and ib), and is achiral. It is called n7eso-2,3-butanediol. 

Since structures 1 and 2 differ only in the arrangement of their atoms in space, they represent stereoisomers. Structures 1 and 2 are also mirror images of each other thus 1 and 2 represent a pair of enantiomers. Structures 3 and 4 correspond to another pair of enantiomers. Structures 1-4 are all different, so there are, in total, four stereoisomers of 2,3-dibromopentane. 

Carbons 2 and 3 of tartaric acid are stereocenters, and, from the 2" rule, the maximum number of stereoisomers possible is 2 = 4. Figure 6.5 shows the two pairs of mirror images of this compound. Structures (a) and (b) are nonsuperposable mirror images and, therefore, are a pair of enantiomers. Structures (c) and (d) are also mirror images, but they are superposable. To see this, imagine that you rotate (d) by 180° in the plane of the paper, lift it out of the plane of the paper, and place it on top of (c). If you do this mental manipulation correctly, you will find that (d) is... 

Arene metal carbonyl complexes containing disubstituted ortho or meta arenes are asymmetric and may be resolved to give enantiomers [structures (10.3)]. 

Functionalized polystyrene resins have been employed for ligand-exchange chromatography of racemates of amino-acids. > The resins carry asymmetric sorbent groups, for example of oc-amino-acids complexed with Cu > or Ni , capable of selective formation of mixed ligands with amino-acid enantiomers. Structures (10) and (11) are examples of reactive sites bonded to polystyrene resins for this purpose. The second type of structure is produced by direct... 

The relationships between the stereoisomeric 2,3,4-trihydroxybutanals are established with mirror planes. Imagine a mirror placed between I and II. Structures I and II are nonsuperimposable mirror images they are enantiomers. Structures III and IV are also nonsuperimposable mirror images. Like all enantiomers, they rotate plane-polarized light in equal and opposite directions. 

These results evidenced that this stationary phase was also able to separate other enantiomers, structurally related to quinine, which contained vicinal amine and hydroxyl functionalities. Taking into account that MAA/quinine ratio was 36 1, the high excess of monomer could be responsible for the formation of strong binding sites in the MIP showing selectivity for the optical antipodes of ephedrine. 

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