Organic Chemistry . William H. Brown & Christopher S. Foote. Chirality. Chapter 3. Isomers. Isomers: different compounds with the same molecular formula Constitutional isomers: isomers with a different connectivity
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William H. Brown &
Christopher S. Foote
1. Each atom bonded to the stereocenter is assigned a priority based on atomic number; the higher the atomic number, the higher the priority
2. If priority cannot be assigned per the atoms bonded to the stereocenter, look to the next set of atoms; priority is assigned at the first point of difference
3. Atoms participating in a double or triple bond are considered to be bonded to an equivalent number of similar atoms by single bonds
1. Locate the stereocenter, identify its four substituents, and assign priority from 1 (highest) to 4 (lowest) to each substituent
2. Orient the molecule so that the group of lowest priority (4) is directed away from you
3. Read the three groups projecting toward you in order from highest (1) to lowest priority (3)
4. If the groups are read clockwise, the configuration is R; if they are read counterclockwise, the configuration is S
Example:a commercial synthesis of naproxen, a nonsteroidal antiinflammatory drug (NSAID), gives this enantiomer in 97% ee. Assign an R or S configuration to its stereocenter, and calculate the % R and S enantiomers in the mixture.
Examples of enantiomerically pure bases
Draw mirror images for each molecule.
Which are identical with (a) and which are mirror images of (a)?
Mark all stereocenters in each molecule.
Assign an R or S configuration to the stereocenter in each enantiomer.
Assign an R or S configuration to this enantiomer of 2-butanol. Also draw a Newman production viewed along the bond between carbons 2 and 3.
Assign an R or S configuration to each stereocenter in this enantiomer of ephedrine.
Assign an R or S configuration to this enantiomer of carbon-14 labeled citric acid.
Draw all stereoisomers possible for this compound. Label which are meso and which are pairs of enantiomers.
Mark are stereocenters in each molecule. How many stereoisomers are possible for each molecule?
Label the eight stereocenters in cholesterol.
Label the four stereocenters in amoxicillin.
Are the formulas in each set identical, enantiomers, or diastereomers?
Which are meso compounds?
Oxidation of this bicyclic alkene gives a dicarboxylic acid. Is the product of this oxidation one enantiomer, a racemic mixture, or a meso compound?
Verify that although, this molecule has no stereocenter, it is chiral.
Verify that, although this substituted allene has no stereocenter, it is chiral.
End of Chapter 3