Organic Chemistry I - Chapter 5

Which of the following configurations corresponds to the structure below?

(4R,5R)

A newly isolated natural product was shown to be optically active. If a solution of 2.0 g in 10 mL of ethanol in a 50 cm tube gives a rotation of +2.57º, what is the specific rotation of this natural product?

+2.57º

A mixture of two enantiomers with a composition of 65.0% R has an observed rotation of -25.3º in a 10.0 cm polarimeter tube. If the mixture has a concentration of 2.038 g/mL at 25ºC, what is the predicted [a]25D of an optically pure sample of the S enantiomer?

+41.3º

If (S)-glyceraldehyde has a specific rotation of -8.7º, what is the specific rotation of (R)-glyceraldehyde?

+8.7º

(-)-lactic acid has a specific rotation of -3.8º. What is the specific rotation of a solution containing 7.5 g of (-)-lactic acid and 2.5 g of (+)-lactic acid?

-1.9º

A student measured the optical activity of an unknown sugar at two different concentrations. The results of his measurements are shown below. Given that the sample cell had a path length of 10.0 cm, calculate the specific rotation for the unknown sugar. (Hint: Consider each measurement of plane polarized light has a true reading and a "ghost" reading 180º from the true reading).

-105º

How many asymmetric carbon atoms are present in the following compound?

0

How many enantiomers are there of the molecule shown below?

0

Given that glucose has a specific rotation of +52.8º. Predict the concentration of a glucose aqueous solution contained in a 10 cm long polarimetry tube if a rotation of +15.8º was observed.

0.299 g/mL

How many asymmetric carbon atoms are present in the following compound?

1

How many asymmetric carbons are present in the compounds below? 3-ethyl-2,2,4-trimethylpentane

1

How many enantiomers are there of the molecule shown below?

1

Which of the following structures are achiral and meso?

1 & 4

How many asymmetric carbon atoms are present in the following compound?

2

How many asymmetric carbons are present in the compounds below?

2

How many diastereomers are there of the molecule shown below?

2

How many asymmetric carbon atoms are present in the following compound?

5

How many asymmetric carbons are present in the compound below?

5

If a mixture contains 75% of one compound and 25% of its enantiomer, what is the e.e. of the mixture?

50

How many diastereomers are there of the molecule shown below?

6

Calculate the e.e. of a mixture containing 8.0 g of (-)-glyceraldehyde and 2.0 g of (+)-glyceraldehyde.

60%

One of the stereoisomers of the following oblongolide structure is a natural product isolated from a fungus and has been found to contain antiviral cytotoxic activities. How many stereoisomers exist for this structure?

64

The specific rotation of pure (-)-2-butanol is -13.5º. What % of a mixture of the two enantiomeric forms is the (+)-form if the specific rotation of this mixture is +7.0º?

76%

Is the molecule shown below chiral or achiral?

Achiral

Is the molecule shown below chiral or achiral? (CH3)3CCH(CH3)2

Achiral

Is the molecule shown below chiral or achiral? CH3CH2CH(CH3)CH2CH3

Achiral

Which of the following molecules, if isolated in its pure form, would demonstrate optical activity?

Both IV and V

Is the molecule shown below chiral or achiral?

Chiral

What is the structural relationship between the two molecule shown below?

Constitutional Isomers

What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,5R)-2,3,5-trichloroheptane?

Constitutional Isomers

What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,3-dimethylcyclopentane?

Constitutional Isomers

Compounds that rotate the plane of polarized light clockwise are called _________.

Dextrorotatory

The relationship between I and II is: ______________.

Diastereomers

The relationship between I and III is: _____________.

Diastereomers

What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2R,3R,4R)-2,3,4-trichloroheptane?

Diastereomers

What term describes the structural relationship between (E)- and (Z)-2-pentene?

Diastereomers

What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,2-dimethylcyclopentane?

Diastereomers

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Diastereomers

Which of the following terms correctly describe(s) the structural relationship between cis-1,3-dimethylcyclopentane and trans-1,3-dimethylcyclopentane?

Diastereomers & geometric isomers

What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,4R)-2,3,4-trichloroheptane?

Enantiomers

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Enantiomers

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Enantiomers has

Which of the structures above are meso structures?

I

A mixture of equal amounts of two enantiomers __________.

Is called a racemic mixture & is optically inactive

Which of the following incorrectly describes cis-1,2-dimethylcyclopentane?

It has an enantiomer.

Captopril is used to treat high blood pressure and congestive heart failure. Label the chiral centers as R or S.

Look at picture

Circle all structures shown below that are chiral.

Look at picture

Circle each chiral molecule among those shown below.

Look at picture

Draw any diastereomer of the molecule shown below.

Look at picture

Draw the Fischer projection of (2R,4R)-2,4-dibromopentane.

Look at picture

Draw the Fischer projection of (S)-2-bromobutane.

Look at picture

Draw the Fischer projection of (S)-2-hydroxybutanoic acid, CH3CH2CH(OH)COOH.

Look at picture

Draw the enantiomer of the molecule shown below.

Look at picture

Draw the structure of (1R,2R)-1-bromo-2-chlorocyclobutane. Take particular care to indicate stereochemistry properly.

Look at picture

Draw the structure of (1R,2S,3S)-1,2-dibromo-3-ethylcyclohexane. Take particular care to indicate stereochemistry properly.

Look at picture

Draw the structure of (2R,3R)-2,3-dibromo-3-chloropentane.

Look at picture

Draw the structure of (2R,3S)-2,3-dichloropentane. Take the particular care to indicate three-dimensional stereochemical detail properly.

Look at picture

Draw the structure of (S)-1-bromo-1-chloropropane. Take the particular care to indicate three-dimensional stereochemical detail properly.

Look at picture

Draw the structure of (S)-3-chloro-3-methylhexane. Take particular care to indicate stereochemistry properly.

Look at picture

Draw the structure of the diastereomer of (2R,3S)-2,3-dichloropentane. Take the particular care to indicate three-dimensional stereochemical detail properly.

Look at picture

Draw the structure of the enantiomer of (2R,3S)-2,3-dichloropentane. Take the particular care to indicate three-dimensional stereochemical detail properly.

Look at picture

Draw the structure of the meso form of 1,3-dichlorocyclopentane. Take particular care to indicate three-dimensional stereochemical detail properly.

Look at picture

For the structure shown below, draw the stereoisomer having a configuration of (1R,3S,4S) in a perspective structure.

Look at picture

If possible, draw the structure of any diastereomer of the molecule shown below.

Look at picture

If possible, draw the structure of the enantiomer of the molecule shown below.

Look at picture

Label each asymmetric carbon in the compound below as R or S.

Look at picture

Label each asymmetric carbon in the molecule below as having the R or S configuration.

Look at picture

Phantasmidine, shown below, is found in poisonous frog skin and has analgesic properties. Assign each chiral center as having either R or S configuration.

Look at picture

Provide a Fischer projection of (2R,3R,4S)-2,3,4-trichloroheptane.

Look at picture

Provide a Fischer projection of (2S,3S,4S)-2,3,4-trichloroheptane.

Look at picture

Translate the structure below to a Fischer projection.

Look at picture

Can the molecule shown below be properly described as a meso compound?

No

Can the molecule shown below be properly described as a meso compound? (CH3)2CHCH2CH3

No

Can one predict whether a compound with a single asymmetric carbon is dextro- or levorotatory based on the R/S assignment at this asymmetric carbon? Explain briefly.

No. R/S assignment is purely a convention of nomenclature and is completely independent of the direction in which plane-polarized light is rotated by the compound.

How many asymmetric carbon atoms are present in the following compound?

None

Which of the following statements is (are) true for the compound cis-1,2-dichlorocyclopropane? The compound is chiral The enantiomer of this compound is trans-1,2-dichlorocyclopropane. This compound contains no asymmetric carbons. All of the above None of the above

None of the above

Can one separate a mixture of enantiomers by gas chromatography? Explain.

Provided the compounds can be volatilized, a mixture of enantiomers can be separated by GC if an appropriate chiral column can be found. Enantiomers will be retained differently by the chiral stationary phase of the column.

Assign the proper configurational label, R or S, to the chiral carbon in the molecule shown below.

R

Label each asymmetric carbon in the compound below as R or S.

R

The process by which enantiomers are separated is called _________.

Resolution

Assign the proper configurational label, R or S, to the chiral carbon in the molecule shown below.

S

Label each asymmetric carbon in the compound below as R or S.

S

______________ are isomers which have the same bonding sequence but differ in the orientation of their atoms in space.

Stereoisomers

Is the mirror image of the following molecule an enantiomer or is it superimposable with it?

Superimposable. The molecule is achiral.

If possible, draw the structure of the enantiomer of the molecule shown below.

The compound is an achiral, meso compound; it has no enantiomer.

Why is the following structure not a meso compound?

The functional group at the top (aldehyde) is different from the bottom (alcohol) and thus there is no internal reflective plane in the molecule.

If possible, draw the enantiomer of the molecule shown below.

The molecule is an achiral. It does not have an enantiomer.

Is the molecule shown below chiral or achiral? Explain what this means.

The molecule is chiral because it's mirror image is nonsuperimposable.

Which of the statements below correctly describes an achiral molecule?

The molecule might be a meso form.

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

The same compound

Briefly describe how two enantiomers might be separated.

The two compounds can be converted by diastereomers, separated based on physical properties of these diastereomers, and subsequently returned to their original forms after separation. Another method involves the chromatographic separation using a chiral stationary phase.

Explain the stereochemical relationship, if any, among the following two structures and describe whether or not they could be theoretically isolated from each other.

These structures are conformationally dependent diastereomers. They could not be isolated because they are actually the same molecule.

Which of the following statements correctly pertains to a pair of enantiomers?

They rotate the plane of polarized light by exactly the same amount and in opposite directions.

Which of the following statements is (are) true for the compound (R)-2-butanol?

This compound is chiral, optically active, and has an enantiomer.

Which of the following statements is (are) true for the compound (3R,4R)-3,4-dimethylhexane?

This compound is chiral, the enantiomer of this compound is (3S,4S)-3,4-dimethylhexane, the compound is a diastereomer of (3R,4S)-3,4-dimethylhexane.

If possible, draw the enantiomer of the molecule shown below.

This molecule is achiral. It does not have an enantiomer.

Can the molecule shown below be properly described as a meso compound?

Yes

Would a 50:50 mixture of (2R,3R)-2,3-dibromobutane and (2R,3S)-2,3-dibromobutane be optically active? Explain.

Yes, the mixture would be optically active. This is not a racemic mixture but a mixture of diastereomers. The specific rotations of diastereomers are not the same in magnitude nor necessarily opposite in sign.

Does the molecule shown below contain asymmetric carbon atoms? Is this molecule chiral?

Yes, the molecule contains 4 asymmetric carbon atoms. No, the molecule is not chiral since it is superimposable with its mirror image.

Is it theoretically possible to separate the pair of compounds below by distillation? Explain briefly.

Yes. The molecules are related as diastereomers and hence have different boiling points.

Can a molecule be chiral if it contains no asymmetric carbons? Explain briefly.

Yes. The presence of asymmetric carbons is not required for a molecule to be chiral. The only requirement is that the molecule be nonsuperimposable with its mirror image. Structural features other than asymmetric carbons can lead to chirality.

Predict the specific rotation of the compound shown.

Zero; the compound is achiral

Stereoisomers which are not mirror image isomers are _________.

diastereomers

Which of the following terms best describes the stereochemical relationship of the two compounds shown below in Fischer notation?

diastereomers