1. Draw  all  the  staggered  and  eclipsed  conformers  that  result  from  rotation  about  the  C2-­‐C3  bond  of  propane    

     2. Sketch  a  potential-­‐energy  diagram  for  rotation  of  the  C2-­‐C3  bond  of  propane  through  360°,  starting  with  

the  least  stable  conformer.      

       3. Given  the  potential-­‐energy  diagram  for  rotation  of  ethane  below,  calculate  the  value  of  the  H-­‐H  eclipsing  

interaction  in  kcal/mol.  

   ΔG  between  staggered  and  eclipsed  =  2.9kcal-­‐1.    Therefore,  3  eclipsed  H-­‐H  interactions  =  2.9  kcal-­‐1                      Thus,  1  eclipsed  H-­‐H  interactions  ~  1.0  kcal-­‐1        4. Which  of  the  following  represent  cis  isomers?  

 

 

H

HHH

H Me

H

H

H

Me

HH

H

HHMe

H H

H

H

H

H

MeH

H

HHH

Me H

H

H

H

H

HMe

H

H

H

Me

HH

Section 2.10 Conformations of Alkanes: Rotation About Carbon–Carbon Bonds 89

will use Newman projections because they are easy to draw and they do a good job ofrepresenting the spatial relationships of the substituents on the two carbon atoms.

The electrons in a bond will repel the electrons in another bond if thebonds get too close to each other. The staggered conformation, therefore, is the moststable conformation of ethane because the bonds are as far away from eachother as possible. The eclipsed conformation is the least stable conformation becausein no other conformation are the bonds as close to one another. The extra ener-gy of the eclipsed conformation is called torsional strain. Torsional strain is the namegiven to the repulsion felt by the bonding electrons of one substituent as they pass closeto the bonding electrons of another substituent. The investigation of the various confor-mations of a compound and their relative stabilities is called conformational analysis.

Rotation about a carbon–carbon single bond is not completely free because of theenergy difference between the staggered and eclipsed conformers. The eclipsed con-former is higher in energy, so an energy barrier must be overcome when rotation aboutthe carbon–carbon bond occurs (Figure 2.4). However, the barrier in ethane is small

C¬H

C¬H

C¬HC¬H

Melvin S. Newman (1908–1993)was born in New York. He receiveda Ph.D. from Yale University in1932 and was a professor ofchemistry at Ohio State Universityfrom 1936 to 1973.

H HH 60°

60°

60°

HH H

H

H

H

H

HH

H

H

H

H

H

H

C C

H H

H HH H

C C

H

HH

H

H

H

HH

HH

HH

perspectiveformulas

sawhorseprojections

Newmanprojections

staggered conformation for rotation about the carbon–carbonbond in ethane

eclipsed conformation for rotation about the carbon–carbonbond in ethane

eclipsed conformers

0° 60° 120°

staggered conformers

eclipsed conformers

180°Degrees of rotation

240° 300° 360°

Pote

ntia

l ene

rgy

2.9 kcal/molor 12 kJ/mol

H

HH

HH

HH

HH

HHH

HHH

H

H H

H

HH

H

H H

H

HH

H

H

HH

HH

H

H

HH

HH

H

H

H

! Figure 2.4Potential energy of ethane as a function of the angle of rotation about the carbon–carbon bond.

3-D Molecule:Staggered and eclipsedconformations of ethane

BRUI02-060_108r4 20-03-2003 11:48 AM Page 89

'6. Given'the'potential9energy'diagram'for'rotation'of'ethane'below,'calculate'

the'value'of'the'H9H'eclipsing'interaction'in'kcal/mol.'''

''7. Which'of'the'following'represent'cis'isomers?''

'

''

8. Draw'clear'conformational'drawings'for'these'molecules,'labeling'each'substituent'as'axial'or'equatorial.''

''9. Draw'the'two'conformations'of'cis919ethyl929methylcyclohexane.'

Determine'which'is'more'stable.''10. In'the'lowest'energy'conformation'of'the'compound'below,'how'many'alkyl'

substituents'are'axial?''

''11. Write'the'structural'formula'for'the'more'stable'conformation'of'each'of'

the'following'compounds.'a. trans-1-Fluoro-3-methylcyclohexane b. cis-1-Iodo-4-methylcyclohexane ! c. cis-1-tert-Butyl-4-methylcyclohexane d. cis-1,3,5-Trimethylcyclohexane

Section 2.10 Conformations of Alkanes: Rotation About Carbon–Carbon Bonds 89

will use Newman projections because they are easy to draw and they do a good job ofrepresenting the spatial relationships of the substituents on the two carbon atoms.

The electrons in a bond will repel the electrons in another bond if thebonds get too close to each other. The staggered conformation, therefore, is the moststable conformation of ethane because the bonds are as far away from eachother as possible. The eclipsed conformation is the least stable conformation becausein no other conformation are the bonds as close to one another. The extra ener-gy of the eclipsed conformation is called torsional strain. Torsional strain is the namegiven to the repulsion felt by the bonding electrons of one substituent as they pass closeto the bonding electrons of another substituent. The investigation of the various confor-mations of a compound and their relative stabilities is called conformational analysis.

Rotation about a carbon–carbon single bond is not completely free because of theenergy difference between the staggered and eclipsed conformers. The eclipsed con-former is higher in energy, so an energy barrier must be overcome when rotation aboutthe carbon–carbon bond occurs (Figure 2.4). However, the barrier in ethane is small

C¬H

C¬H

C¬HC¬H

Melvin S. Newman (1908–1993)was born in New York. He receiveda Ph.D. from Yale University in1932 and was a professor ofchemistry at Ohio State Universityfrom 1936 to 1973.

H HH 60°

60°

60°

HH H

H

H

H

H

HH

H

H

H

H

H

H

C C

H H

H HH H

C C

H

HH

H

H

H

HH

HH

HH

perspectiveformulas

sawhorseprojections

Newmanprojections

staggered conformation for rotation about the carbon–carbonbond in ethane

eclipsed conformation for rotation about the carbon–carbonbond in ethane

eclipsed conformers

0° 60° 120°

staggered conformers

eclipsed conformers

180°Degrees of rotation

240° 300° 360°

Pote

ntia

l ene

rgy

2.9 kcal/molor 12 kJ/mol

H

HH

HH

HH

HH

HHH

HHH

H

H H

H

HH

H

H H

H

HH

H

H

HH

HH

H

H

HH

HH

H

H

H

! Figure 2.4Potential energy of ethane as a function of the angle of rotation about the carbon–carbon bond.

3-D Molecule:Staggered and eclipsedconformations of ethane

BRUI02-060_108r4 20-03-2003 11:48 AM Page 89

Problems 107

a. 4-bromo-3-pentanol g. 3,3-dichlorooctaneb. 2,2-dimethyl-4-ethylheptane h. 5-ethyl-2-methylhexanec. 5-methylcyclohexanol i. 1-bromo-4-pentanold. 1,1-dimethyl-2-cyclohexanol j. 3-isopropyloctanee. 5-(2,2-dimethylethyl)nonane k. 2-methyl-2-isopropylheptanef. isopentyl bromide l. 2-methyl-N,N-dimethyl-4-hexanamine

49. Which of the following diaxial-substituted cyclohexanes has the highest energy?

50. Give systematic names for all the alkanes with molecular formula that do not have any secondary hydrogens.

51. Draw skeletal structures of the following compounds:a. 5-ethyl-2-methyloctane d. propylcyclopentaneb. 1,3-dimethylcyclohexane e. 2-methyl-4-(1-methylethyl)octanec. 2,3,3,4-tetramethylheptane f. 2,6-dimethyl-4-(2-methylpropyl)decane

52. For rotation about the bond of 2-methylhexane:a. Draw the Newman projection of the most stable conformer.b. Draw the Newman projection of the least stable conformer.c. About which other carbon–carbon bonds may rotation occur?d. How many of the carbon–carbon bonds in the compound have staggered conformers that are all equally stable?

53. Which of the following structures represents a cis isomer?

54. Draw all the isomers that have the molecular formula (Hint: There are eight such isomers.)a. Give the systematic name for each of the isomers. d. How many of the isomers are primary alkyl halides?b. Give a common name for each isomer that has one. e. How many of the isomers are secondary alkyl halides?c. How many isomers do not have common names? f. How many of the isomers are tertiary alkyl halides?

55. Give the systematic name for each of the following compounds:

a. d. g.

b. e. h.

c. f.

56. Draw the two chair conformers of each compound, and indicate which conformer is more stable:a. cis-1-ethyl-3-methylcyclohexane d. trans-1-ethyl-3-methylcyclohexaneb. trans-1-ethyl-2-isopropylcyclohexane e. cis-1-ethyl-3-isopropylcyclohexanec. trans-1-ethyl-2-methylcyclohexane f. cis-1-ethyl-4-isopropylcyclohexane

57. Why are alcohols of lower molecular weight more soluble in water than those of higher molecular weight?58. The most stable conformer of N-methylpiperidine is shown on p. 108.

a. Draw the other chair conformer.

OOH

NH2Cl

OH

C5H11Br.

CH3

CH3 CH3

CH3

CH3

CH3 CH3

CH3

A B C D

C-3¬C-4

C7H16

A B C

CH3 CH3

CH3Cl Cl Cl

BRUI02-060_108r4 20-03-2003 11:48 AM Page 107

CH3

OH

CH3

OH

CH3

OH21) In the lowest energy chair conformation of cis-1,3-dimethylcyclohexane, how many axial positions are

occupied by hydrogen atoms?

A) 2 B) 3 C) 4 D) 5 E) 6

22) Arrange the following conformers of butane in order of energy, lowest to highest: eclipsed, totallyeclipsed, gauche, and anti.

23) In the lowest energy conformation of the compound below, how many alkyl substituents are axial?

CH3

A) 0 B) 1 C) 2 D) 3 E) 6

A B C D

trans trans cis cis

Note:  all  staggered  are  identical,  as  with  all  eclipsed.  Thus  their  energy  levels  are  identical  

 5. In  the  lowest  energy  conformation  of  the  compound  below,  how  many  of  the  axial  substituents  are  axial?  

 

     6. Draw  Fischer  projections  of  the  following  compounds.    

     

   

7. Draw  projection  structures  of  the  following  compounds  in  the  most  stable  conformation.    

   

   

8. How  many  stereocenters  does  the  following  compound  have?  Identify  them.    

8  stereocenters    

'6. Given'the'potential9energy'diagram'for'rotation'of'ethane'below,'calculate'

the'value'of'the'H9H'eclipsing'interaction'in'kcal/mol.'''

''7. Which'of'the'following'represent'cis'isomers?''

'

''

8. Draw'clear'conformational'drawings'for'these'molecules,'labeling'each'substituent'as'axial'or'equatorial.''

''9. Draw'the'two'conformations'of'cis919ethyl929methylcyclohexane.'

Determine'which'is'more'stable.''10. In'the'lowest'energy'conformation'of'the'compound'below,'how'many'alkyl'

substituents'are'axial?''

''11. Write'the'structural'formula'for'the'more'stable'conformation'of'each'of'

the'following'compounds.'a. trans-1-Fluoro-3-methylcyclohexane b. cis-1-Iodo-4-methylcyclohexane ! c. cis-1-tert-Butyl-4-methylcyclohexane d. cis-1,3,5-Trimethylcyclohexane

Section 2.10 Conformations of Alkanes: Rotation About Carbon–Carbon Bonds 89

will use Newman projections because they are easy to draw and they do a good job ofrepresenting the spatial relationships of the substituents on the two carbon atoms.

The electrons in a bond will repel the electrons in another bond if thebonds get too close to each other. The staggered conformation, therefore, is the moststable conformation of ethane because the bonds are as far away from eachother as possible. The eclipsed conformation is the least stable conformation becausein no other conformation are the bonds as close to one another. The extra ener-gy of the eclipsed conformation is called torsional strain. Torsional strain is the namegiven to the repulsion felt by the bonding electrons of one substituent as they pass closeto the bonding electrons of another substituent. The investigation of the various confor-mations of a compound and their relative stabilities is called conformational analysis.

Rotation about a carbon–carbon single bond is not completely free because of theenergy difference between the staggered and eclipsed conformers. The eclipsed con-former is higher in energy, so an energy barrier must be overcome when rotation aboutthe carbon–carbon bond occurs (Figure 2.4). However, the barrier in ethane is small

C¬H

C¬H

C¬HC¬H

Melvin S. Newman (1908–1993)was born in New York. He receiveda Ph.D. from Yale University in1932 and was a professor ofchemistry at Ohio State Universityfrom 1936 to 1973.

H HH 60°

60°

60°

HH H

H

H

H

H

HH

H

H

H

H

H

H

C C

H H

H HH H

C C

H

HH

H

H

H

HH

HH

HH

perspectiveformulas

sawhorseprojections

Newmanprojections

staggered conformation for rotation about the carbon–carbonbond in ethane

eclipsed conformation for rotation about the carbon–carbonbond in ethane

eclipsed conformers

0° 60° 120°

staggered conformers

eclipsed conformers

180°Degrees of rotation

240° 300° 360°

Pote

ntia

l ene

rgy

2.9 kcal/molor 12 kJ/mol

H

HH

HH

HH

HH

HHH

HHH

H

H H

H

HH

H

H H

H

HH

H

H

HH

HH

H

H

HH

HH

H

H

H

! Figure 2.4Potential energy of ethane as a function of the angle of rotation about the carbon–carbon bond.

3-D Molecule:Staggered and eclipsedconformations of ethane

BRUI02-060_108r4 20-03-2003 11:48 AM Page 89

Problems 107

a. 4-bromo-3-pentanol g. 3,3-dichlorooctaneb. 2,2-dimethyl-4-ethylheptane h. 5-ethyl-2-methylhexanec. 5-methylcyclohexanol i. 1-bromo-4-pentanold. 1,1-dimethyl-2-cyclohexanol j. 3-isopropyloctanee. 5-(2,2-dimethylethyl)nonane k. 2-methyl-2-isopropylheptanef. isopentyl bromide l. 2-methyl-N,N-dimethyl-4-hexanamine

49. Which of the following diaxial-substituted cyclohexanes has the highest energy?

50. Give systematic names for all the alkanes with molecular formula that do not have any secondary hydrogens.

51. Draw skeletal structures of the following compounds:a. 5-ethyl-2-methyloctane d. propylcyclopentaneb. 1,3-dimethylcyclohexane e. 2-methyl-4-(1-methylethyl)octanec. 2,3,3,4-tetramethylheptane f. 2,6-dimethyl-4-(2-methylpropyl)decane

52. For rotation about the bond of 2-methylhexane:a. Draw the Newman projection of the most stable conformer.b. Draw the Newman projection of the least stable conformer.c. About which other carbon–carbon bonds may rotation occur?d. How many of the carbon–carbon bonds in the compound have staggered conformers that are all equally stable?

53. Which of the following structures represents a cis isomer?

54. Draw all the isomers that have the molecular formula (Hint: There are eight such isomers.)a. Give the systematic name for each of the isomers. d. How many of the isomers are primary alkyl halides?b. Give a common name for each isomer that has one. e. How many of the isomers are secondary alkyl halides?c. How many isomers do not have common names? f. How many of the isomers are tertiary alkyl halides?

55. Give the systematic name for each of the following compounds:

a. d. g.

b. e. h.

c. f.

56. Draw the two chair conformers of each compound, and indicate which conformer is more stable:a. cis-1-ethyl-3-methylcyclohexane d. trans-1-ethyl-3-methylcyclohexaneb. trans-1-ethyl-2-isopropylcyclohexane e. cis-1-ethyl-3-isopropylcyclohexanec. trans-1-ethyl-2-methylcyclohexane f. cis-1-ethyl-4-isopropylcyclohexane

57. Why are alcohols of lower molecular weight more soluble in water than those of higher molecular weight?58. The most stable conformer of N-methylpiperidine is shown on p. 108.

a. Draw the other chair conformer.

OOH

NH2Cl

OH

C5H11Br.

CH3

CH3 CH3

CH3

CH3

CH3 CH3

CH3

A B C D

C-3¬C-4

C7H16

A B C

CH3 CH3

CH3Cl Cl Cl

BRUI02-060_108r4 20-03-2003 11:48 AM Page 107

CH3

OH

CH3

OH

CH3

OH21) In the lowest energy chair conformation of cis-1,3-dimethylcyclohexane, how many axial positions are

occupied by hydrogen atoms?

A) 2 B) 3 C) 4 D) 5 E) 6

22) Arrange the following conformers of butane in order of energy, lowest to highest: eclipsed, totallyeclipsed, gauche, and anti.

23) In the lowest energy conformation of the compound below, how many alkyl substituents are axial?

CH3

A) 0 B) 1 C) 2 D) 3 E) 6

most stable,0 axial substituents

HO

Br

OH

O

H

CH2CH2Br

Br CH2CH2CH3H

CH2CH2Br

H3CH2CH2C H

Br

CHO

HO H

OH

Br HHO

Br

OH

O

H

HO

Br

HO

O

H

H

H

HO

O

H

H

OH

HBr

CHO

HO H

OH

Br H

CH2CH2Br

H3CH2CH2C H

Br

BrH2CH2C

BrCH2CH2CH3H

CHOHOH

OHHBr

234 C H A P T E R 5 Stereochemistry

58. a. Give the product(s) that would be obtained from the reaction of cis-2-butene and trans-2-butene with each of the followingreagents. If the products can exist as stereoisomers, show which stereoisomers are obtained.1. HCl 5.2. followed by 6.3. 7.4. in 8.

b. With which reagents do the two alkenes react to give different products?

59. Which of the following compounds have an achiral stereoisomer?a. 2,3-dichlorobutane f. 2,4-dibromopentaneb. 2,3-dichloropentane g. 2,3-dibromopentanec. 2,3-dichloro-2,3-dimethylbutane h. 1,4-dimethylcyclohexaned. 1,3-dichlorocyclopentane i. 1,2-dimethylcyclopentanee. 1,3-dibromocyclobutane j. 1,2-dimethylcyclobutane

60. Give the products and their configurations obtained from the reaction of 1-ethylcyclohexene with the following reagents:a. HBr d. followed by b. e.c.

61. Citrate synthase, one of the enzymes in the series of enzyme-catalyzed reactions known as the Krebs cycle, catalyzes the synthesisof citric acid from oxaloacetic acid and acetyl-CoA. If the synthesis is carried out with acetyl-CoA that has radioactive carbon

in the indicated position, the isomer shown here is obtained.

a. Which stereoisomer of citric acid is synthesized, R or S?b. Why is the other stereoisomer not obtained?c. If the acetyl-CoA used in the synthesis does not contain will the product of the reaction be chiral or achiral?

62. Give the products of the following reactions. If the products can exist as stereoisomers, show which stereoisomers are obtained.a. f.b. g.c. h.d. i.e. j.

63. The specific rotation of (R)- -glyceraldehyde is If the observed specific rotation of a mixture of (R)-glyceraldehyde and(S)-glyceraldehyde is what percent of glyceraldehyde is present as the R enantiomer?

64. Indicate whether each of the following structures is (R)-2-chlorobutane or (S)-2-chlorobutane. (Use models, if necessary.)

a. c. e.

b. d. f.

65. A solution of an unknown compound (3.0 g of the compound in 20 mL of solution), when placed in a polarimeter tube 2.0 dmlong, was found to rotate the plane of polarized light 1.8° in a counterclockwise direction. What is the specific rotation of thecompound?

Cl

C

CH3

H

Cl CH2CH3H

H

CH3

CH3

H

H Cl

Cl

CH3

H Cl

CH2CH3

H

H

Cl

H

H3C

H CH3

+1.4°,+8.7°.(+)

Pt>C1-chloro-2-ethylcyclohexene + H2,1,2-dimethylcyclohexene + HClPt>C(Z)-3,4-dimethyl-3-heptene + H2,1,2-diethylcyclohexene + H3O+Pt>C(E)-3,4-dimethyl-3-heptene + H2,1-ethylcyclohexene + H3O+

3,3-dimethyl-1-pentene + Br2>CH2Cl2trans-2-pentene + HClPt>C1,2-dideuteriocyclohexene + H2,cis-2-pentene + HCl

14C,

CH2COOH

CH2COOH14

COOHCCH3CSCoA

14

HO

citrate synthaseO

HOOCCH2CCOOH

O

+oxaloacetic acid acetyl-CoA

citric acid

(14C)

Pt>CH2,Br2>CH2Cl2HBr + peroxide

H2O2HO-,BH3>THF

HCl + CH3OHCH2Cl2Br2

HCl + H2OHBr + peroxideH2>Pt>CH2O2HO-,BH3>THFBr2 + H2O

BRUI05-182_237r4 20-03-2003 3:36 PM Page 234

Problems 233

g. h.

56. Mevacor® is used clinically to lower serum cholesterol levels. How many asymmetric carbons does Mevacor® have?

57. Indicate whether each of the following pairs of compounds are identical or are enantiomers, diastereomers, or constitutionalisomers:a. i.

b. j.

c. k.

d. l.

e. m.

f. n.

g. o.

h. p. ClCl and

ClClC

H

CH3 andCH3CH2

CH2Cl

C

H

CH2ClCH3

CH2CH3

C

C

H andCl

HCH3

CH3

CH2CH3

C

C

CH3H

ClH

CH2CH3

CH3

CH2OHHand

CH2CH3

CH3CH3

CH2CH3

CH2OH

H

CH3

CH3and

H3C

CH3

CH3

H3C

and

CH2CH3

CH3

Br

and

H3C

H3C

HH CH3

CH3

C C

Br

C CC Cand

H3C

H

H

CH3H3C

Br

CH3

Br

C C C C

CH3

HO H andH Cl

CH3

CH3

H OHCl H

CH3

CH2CH3

HO H andH Cl

CH3

CH3

HO HH Cl

CH2CH3

CH3

CH3Hand

CH3

H3C

H

HHBr

H

H

Brand

H

Br

H

Br

andH

Br H H

Br Br H

Br

H Cland

Cl H

Cl H

H Cl

H Cland

Cl H

H H

Cl Cl

H Cl and

H Cl

H H

Cl Cl

Mevacor

CH3

OHO

OO

OCH3

H3C

CH2CH3

HO HH Cl

CH3

CH2CH2CH2OHHO CH3

CH2OH

BRUI05-182_237r4 20-03-2003 3:36 PM Page 233

CH2CH3HO H

CH3

H Cl

CH2CH3HO H

CH3

H ClH3CH2C

OH

H

CH3H

Cl

CH3H3CH2C

HClH OHH3CH2C CH3

H

HHO

Cl

CH3H Cl

CH2CH3

CH3H Cl

CH2CH3

H3C

H3CH2CHCl CH3

H3CH2C HCl

O

HO

CH3

H3C

O

O

CH3

O*

*

*

* * *

*

*

Problems 235

66. Butaclamol is a potent antipsychotic that has been used clinically in the treatment of schizophrenia. How many asymmetriccarbons does Butaclamol® have?

67. Which of the following objects are chiral?a. a mug with DAD written on one side e. an automobileb. a mug with MOM written on one side f. a wineglassc. a mug with DAD written opposite the handle g. a naild. a mug with MOM written opposite the handle h. a screw

68. Explain how R and S are related to and

69. Give the products of the following reactions. If the products can exist as stereoisomers, show which stereoisomers are obtained.a. g.b. h.c. i.d. j.e. k.f. l.

70. a. Draw all possible stereoisomers for the following compound.

b. Which isomers are optically inactive (will not rotate plane-polarized light)?

71. Indicate the configuration of the asymmetric carbons in the following molecules:

a. b. c.

72. a. Draw all the isomers with molecular formula that contain a cyclobutane ring. (Hint: There are seven.)b. Name the compounds without specifying the configuration of any asymmetric carbons.c. Identify:

1. constitutional isomers 5. achiral compounds2. stereoisomers 6. meso compounds3. cis–trans isomers 7. enantiomers4. chiral compounds 8. diastereomers

73. A compound has a specific rotation of A solution of the compound has an observed rotation of when placed in a polarimeter tube 10 cm long. What is the percent of each enantiomer in the solution?

74. Draw structures for each of the following molecules:a. (S)-1-bromo-1-chlorobutane d. a chiral isomer of 1,2-dibromocyclobutaneb. (2R,3R)-2,3-dichloropentane e. two achiral isomers of 3,4,5-trimethylheptanec. an achiral isomer of 1,2-dimethylcyclohexane

-6.52°(0.187 g>mL)-39.0°.

C6H12

H3C CH2CH3

BrBr

C C H

HBr OCH

C C

OHHOH

HCH2CH2CH3

CH2CH2Br

HCBr

OH

HOCH2CH CHCH2OHCH

OH OH

Pt>C(E)-3,4-dimethyl-3-hexene + H2,cis-3-hexene + Br2>CH2Cl2

Pt>C(Z)-3,4-dimethyl-3-hexene + H2,trans-3-hexene + Br2>CH2Cl2

Pt>C(E)-2,3-dichloro-2-butene + H2,1-butene + HBr + peroxidePt>C(Z)-2,3-dichloro-2-butene + H2,1-butene + HCl

cis-2-butene + HBr + peroxidetrans-2-pentene + Br2>CH2Cl2

3,3-dimethyl-1-pentene + HBrcis-2-pentene + Br2>CH2Cl2

(-).(+ )

OH

H

N

H

Butaclamol

C(CH3)3

BRUI05-182_237r4 20-03-2003 3:36 PM Page 235

 9. Assign  R/S  configuration  to  all  the  stereocenters  of  the  following  compound.  

 

     10. Natural  epinephrine,   𝛼 !

!"  =  -­‐50°  is  used  medicinally.  Its  enantiomer  is  medically  worthless.  You  are  given  a  solution  said  to  contain  1g  of  epinephrine  in  20  ml  of  liquid,  but  the  optical  purity  is  not  specified.  You  place  in  a  polarimeter  (10  cm  tube),  at  25  °C,  with  a  Na  D-­‐line  light  source  and  get  a  reading  of  -­‐2.5°.  What  is  the  optical  purity  of  the  liquid?    

𝛼 !!"  =  α/(l  x  c)      =    -­‐2.5°  /(1  dm  x  0.05  g/cm3)    =    -­‐50°  

 optical  purity  =  [α]liquid/[α]natural  ephedrine                            =  (-­‐50°/-­‐50°)*100%    =  100%      

N

H

C(CH3)3OH

H12

3

4S Rreverse

S12

2

1

33

4

4

OH

C

(H3C)3CC

2 1

34R