Fischer projections optical activity

In a Fischer projection of representing an optically active compound, an asymmetric atom is shown at the intersection point of two lines of a cross. The horizontal lines going to left and right of this point are the bonds extending forward from the plane of paper. The two vertical lines going to top and bottom are those going back away from the plane of paper. For example 2-iodobutane can be represented as ... 

The (I ,S)-nomenclature still reminds the user of the right and left handed helical pattern arising from Fresnel s 29> interpretation of optical activity. These patterns are characterized by the combination of a translational and a rotational direction. The Ta skeletal symmetry of tetracoordinate systems submits itself to the pictorial models not applicable to other configurational types. The CIP rules may as well be used to define a configurational nomenclature on the basis of the Fischer projection. If one specified that in such a projection of an (R)-... 

Enantiomers have very similar chemical properties, but they rotate polarized light in opposite directions (optical activity, see pp. 36,58). The same applies to the enantiomers of lactic acid. The dextrorotatory L-lactic acid occurs in animal muscle and blood, while the D form produced by microorganisms is found in milk products, for example (see p.l48). The Fischer projection is often used to represent the formulas for chiral centers (cf.p. 58). 

Problem 5.34 For the following reactions give the number of stereoisomers that are isolated, their R.S configurations and their optical activities. Use Fischer projections. 

Problem 6.56 (a) Br, is added to (S)-H2C=CHCHBrCH,. Give Fischer projections and R,S designations for the products. Are the products optically active (b) Repeat (a) with HBr. ... 

Because the hydroxyl group at C-4 of ( (-arabinose is at the right in a Fischer projection formula (evidence of step 1), the hydroxyl at C-2 must be to the left in order for the aldaric acid to be optically active. 

Because both (+)-glucose and (+)-mannose yield optically active aldaric acids and both have the same configuration at C-4, the hydroxyl group must lie at the right in the Fischer projection at this carbon. 

Circle the Fischer projection that shows a plane of symmetry. Underline all the Fischer projections that would be optically active. 

The Fischer projection formula for D-glucose (Example 2.3) is also known as the open- or straight-chain structure. This structure occurs only in solution. There are two crystalline forms of D-glucose, known as a and /3, which also have different optical activities when dissolved. X-ray diffraction studies have confirmed chemical evidence that a- and /3-D-glucose are structures containing a ring of five carbon atoms and one oxygen atom ... 

Stereoisomers Rotation of Plane-Polarized Light The Relationship between Molecular Structure and Optical Activity Fischer Projection Formulas... 

Monosaccharides have chiral centers and thus exhibit optical activity. Let s explore the structure of glyceraldehyde. In the three-dimensional representation, the dotted wedges indicate the bonds that extent backwards from the chiral carbon (away from you or into the plane of the page) and the solid wedges indicate the bonds that are projected toward you (out of the plane of the page). In stereochemistry, Fischer projection is an important way to represent the spatial orientation of molecules. In Fischer projection representation, the bonds that are pointed backward (away from you or into the page) are indicated by vertical lines, and the bonds that extend toward you (out of the page) are represented by horizontal lines. For a more detailed approach, refer to Chapter 19 (Stereochemistry). 

We can be sure that the aldotetroses that we obtain from this Kiliani—Fischer synthesis are both D sugars because the starting compound is D-glyceraldehyde and its chirality center is unaffected by the synthesis. On the basis of the Kiliani—Fischer synthesis, we cannot know just which aldotetrose has both —OH groups on the right and which has the top —OH on the left in the Fischer projection. However, if we oxidize both aldotetroses to aldaric acids, one [d-(—)-erythrose] will yield an optically inactive (meso) product while the other [d-(—)-threose] will yield a product that is optically active (see Practice Problem 22.7). 

D-(—)-eiythrose (use Fischer projections), (b) The two epimeric aldopentoses that one obtains are d-(—)-arabinose and D-(—)-ribose. Nitric acid oxidation of d-(—)-ribose yields an optically inactive aldaric acid, whereas similar oxidation of D-(—)-arabinose yields an optically active product. On the basis of this information alone, which Fischer projection represents d-(—)-arabinose and which represents D-(—)-ribose ... 

Draw Fischer projections for the product(s) formed by the reaction of D-galactose with the following compounds, and state whether each product is optically active or optically inactive (See Example 17.6)... 

All optically active derivatives are called d or l, based on the configuration of carbon 6. The configuration of carbon 6 is found by viewing the Fischer-type projection (p. 9) with carbons 5 and 1 away from the viewer and C-5 at the top. When an optically inactive cyclitol has been made asymmetric by substitution, the d or l is put at the beginning of the name, e.g., D-l-O-methyl-mwco-inositol, but 3-0-methyl-D-inositol. When an inositol derivative contains less than six asymmetric carbon atoms, it is named as a derivative of the related inositol that has the maximum number of CIS OH groups. If this leads to more than one possibility, the parent inositol is chosen that has the lowest possible number for its substituents CIS to the OH on carbon 1. 

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