Next time you have the opportunity to view a collection of

Following are stereorepresentations for the four stereoisomers of 3-chloro-2-butanol. CH3 CH3 (1) OH H H Cl CH3 CH3 (3) H Cl HO H CH3 CH3 (4) H H HO Cl CH3 CH3 (2) OH Cl H H (a) Assign an R or S confi guration of each chiral center. (b) Which compounds are enantiomers? (c) Which compounds are diastereomers?

Following are four Newman projection formulas for tartaric acid. COOH COOH COOH COOH COOH OH COOH COOH (1) H OH H OH (2) HO H H OH H (3) HOOC HO H OH (4) H HO H (a) Which represent the same compound? (b) Which represent enantiomers? (c) Which represent a meso compound? (d) Which are diastereomers?

Give a complete stereochemical name for the following compound, which is a 1,2,3-butanetriol. HO H HO H CH3 CH2OH

How many stereoisomers exist for 1,3-cyclopentanediol?

How many stereoisomers exist for 1,4-cyclohexanediol?

The specifi c rotation of progesterone, a female sex hormone, is 1172. Calculate the observed rotation for a solution prepared by dissolving 300 mg of progesterone in 15.0 mL of dioxane and placing it in a sample tube 10.0 cm long

One commercial synthesis of naproxen (the active ingredient in Aleve and a score of other over-the- counter and prescription nonsteroidal anti-infl ammatory drug preparations) gives the enantiomer shown in 97% enantiomeric excess. C COOH H CH3 H3CO Naproxen (a nonsteroidal anti- inflammatory drug) (a) Assign an R or S confi guration to this enantiomer of naproxen. (b) What are the percentages of R and S enantiomers in the mixture?

Think about the helical coil of a telephone cord or a spiral binding and suppose that you view the spiral from one end and fi nd that it is a left-handed twist. If you view the same spiral from the other end, is it a right-handed or left-handed twist?

Next time you have the opportunity to view a collection of sea shells that have a helical twist, study the chirality of their twists. Do you fi nd an equal number of left-handed and right-handed spiral shells or mostly all of the same chirality? What about the handedness of different species of spiral shells?

One reason we can be sure that sp3 -hybridized carbon atoms are tetrahedral is the number of stereoisomers that can exist for different organic compounds. (a) How many stereoisomers are possible for CHCl3, CH2Cl2, and CHClBrF if the four bonds to carbon have a tetrahedral arrangement? (b) How many stereoisomers would be possible for each of these compounds if the four bonds to the carbon had a square planar geometry?

Which compounds contain chiral centers? (a) 2-Chloropentane (b) 3-Chloropentane (c) 3-Chloro-1- pentene (d) 1,2-Dichloropropane

Using only C, H, and O, write structural formulas for the lowest-molecular-weight chiral: (a) Alkane (b) Alcohol (c) Aldehyde (d) Ketone (e) Carboxylic acid (f) Carboxylic ester

Draw mirror images for these molecules. Are they different from the original molecule? C OH OH H3C COOH H C CHO CH2OH CH3 CH3 CH3 CH3 H OH C CH3 COOH H2N H OH OH H OH H (a) (e) (f) (g) (h) (b) (c) (d) H OH H OH O

Following are several stereorepresentations for lactic acid. Take (a) as a reference structure. Which stereorepresentations are identical with (a), and which are mirror images of (a)? C OH COOH H3C H C H HOOC CH3 HO C H COOH HO CH3 C H COOH CH3 HO (a) (b) (c) (d

Mark each chiral center in the following molecules with an asterisk. How many stereoisomers are possible for each molecule? O CH3CCH"CH2 CH3CH2CHCH"CH2 CH3 OH CH3CHCHCOOH CH3 NH2 HCOH COOH CH3 (a) (b) HCOH CH2OH CH2OH OH HOCCOOH CH2COOH CH2COOH (e) (f) (g) (c) (d) CH3CCH2CH3

Show that butane in a gauche conformation is chiral. Do you expect that resolution of butane at room temperature is possible?

Assign priorities to the groups in each set. (a) H CH3 OH CH2OH (b) CH2CH"CH2 CH"CH2 CH3 CH2COOH (c) CH3 H COO2 NH3 1 (d) CH3 CH2SH NH3 1 CHO

Following are structural formulas for the enantiomers of carvone. Each has a distinctive odor characteristic of the source from which it is isolated. Assign an R or S confi guration to the single chiral center in each enantiomer. Why do they smell different when they are so similar in structure? O C H H2C CH3 CH3 O H C H CH2 3C CH3 ()Carvone (+)Carvone Spearmint oil Caraway and dill seed oil

Following is a staggered conformation for one of the enantiomers of 2-butanol. H H H OH CH3 H3C (a) Is this (R)-2-butanol or (S)-2-butanol? (b) Draw a Newman projection for this staggered conformation, viewed along the bond between carbons 2 and 3. (c) Draw a Newman projection for two more staggered conformations of this molecule. Which of your conformations is the most stable? Assume that !OH and !CH3 are comparable in size

For centuries, Chinese herbal medicine has used extracts of Ephedra sinica to treat asthma. Ephedra as an herbal supplement has been implicated in the deaths of several athletes, and has recently been banned as a dietary supplement. Phytochemical investigation of this plant resulted in isolation of ephedrine, a very potent dilator of the air passages of the lungs. Ephedrine also has profound effects on the cardiovascular system. The naturally occurring stereoisomer is levorotatory and has the following structure. Assign an R or S confi guration to each chiral center. C C CH3 NHCH3 H H HO Ephedrine []21 D 41

When oxaloacetic acid and acetyl-coenzyme A (acetyl-CoA) labeled with radioactive carbon-14 in position 2 are incubated with citrate synthase, an enzyme of the tricarboxylic acid cycle, only the following enantiomer of [2-14C]citric acid is formed stereoselectively. Note that citric acid containing only 12C is achiral. Assign an R or S confi guration to this enantiomer of [2-14C]citric acid. Note: Carbon-14 has a higher priority than carbon-12. Oxaloacetic acid Acetyl-CoA [2-14C]Citric acid citrate synthase C 14CH2COOH CH2COOH HOOC OH O CH2COOH C9COOH O 14CH3CSCoA

Draw stereorepresentations for all stereoisomers of this compound. Label those that are meso compounds and those that are pairs of enantiomers. COOH H3C CH3 HOOC

Mark each chiral center in the following molecules with an asterisk. How many stereoisomers are possible for each molecule? OH O COOH O OH OH OH CH3CHCHCOOH HO OH CH9COOH CH29COOH HO9CH9COOH (a) (b) (c) (e) (f) (g) (h)

bel the eight chiral centers in cholesterol. How many stereoisomers are possible for a molecule with this many chiral centers? HO

Label the four chiral centers in amoxicillin, which belongs to the family of semisynthetic penicillins. HO CH9C9HN CH3 CH3 C NH2 Amoxicillin HO O O O N S

If the optical rotation of a new compound is measured and found to have a specifi c rotation of 140, how can you tell if the actual rotation is not really 140 plus some multiple of 1360? In other words, how can you tell if the rotation is not actually a value such as 1400 or 1760?

Are the formulas within each set identical, enantiomers, or diastereomers? Cl H H OH HO H H Cl (a) (b) ClH HHO ClH OHH and and HO H Cl H (c) ClH HHO and

Which of the following are meso compounds? (a) (b) H OH H OH CH2OH CH2OH CH3 OH HO C C Br Br H H CH3 CH3 CH3 (c) CH3 CH3 OH HO (e) (f) (g) (i) OH OH (d) (h) C C Br Br H H CH3 CHO CH2OH CH2OH CH2OH H OH H OH CH2OH HO H H OH CH2OH H OH H OH

Vigorous oxidation of the following bicycloalkene breaks the carbon-carbon double bond and converts each carbon of the double bond to a COOH group. Assume that the conditions of oxidation have no effect on the confi guration of either the starting bicycloalkene or the resulting dicarboxylic acid. Is the dicarboxylic acid produced from this oxidation one enantiomer, a racemic mixture, or a meso compound? HOOC COOH

A long polymer chain, such as polyethylene (!CH2CH2!)n, can potentially exist in solution as a chiral object. Give two examples of chiral structures that a polyethylene chain could adopt

Which of the following compounds are chiral? Which, if any, are meso? Which, if any, does not have a possible diastereomer? (a) (b) (c) (d)

Will the following compound show any optical activity if there is restricted rotation along the central C!C bond? What will happen to the optical activity at elevated temperatures as the rotation becomes less restricted? H Cl CH3

Are the following structures chiral as drawn? When placed in a solution at 298 K, which structure will show an optical rotation? Explain. (a) (b) (c) (d) (e) (f)

To the following statements, answer True or False and explain your answer. (a) All chiral centers are also stereocenters. (b) All stereocenters are also chiral centers. (c) All chiral molecules are optically active when pure. (d) All mixtures of chiral molecules are optically active. (e) To be optically active, a molecule must have a chiral center. (f) To be meso, a molecule must have at least two chiral centers

The chiral catalyst (R)-BINAP-Ru is used to hydrogenate alkenes to give alkanes (Section 6.7C). The products are produced with high enantiomeric excess. An example is the formation of (S)-naproxen, a pain reliever. (S)-Naproxen (ee > 98%) Ph = C6H5 (R )-BINAP-Ru pressure H CH3 PPh2 PPh2 COOH CH2 COOH H3CO H3CO H2 BINAP (a) What kind of isomers are the enantiomers of BINAP? (b) How can one enantiomer of naproxen be formed in such high yield?

n Section 10.5D, the following reactions are discussed. Ts is the toluenesulfonate group. 9S9 Toluenesulfonate group (Ts) CH39 O O (S)-2-Octanol OH Cl9Ts (S)-2-Octyl tosylate OTs HCl pyridine (a) SN2 ethanol Sodium acetate (R)-2-Octyl acetate O NaOTs? O?Na (S)-2-Octyl tosylate O OTs O (b) In reaction (a), an S compound gives an S product. In reaction (b), an S compound gives an R product. Explain what is probably going on. (Hint: The oxygen atom in the starting material and product is the same in one reaction but not in the other.) What might this say about the second reaction? 5498