Problem 5-3€¦ · the left is the oxygen (hydroxyl group), then the ethyl group, then the methyl group, and the lowest priority is the hydrogen. When the hydrogen is oriented away

9/7/2018 ASSIGNMENT 2: Task 2

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ASSIGNMENT 2: Task 2Due: 11:59pm on Monday, September 17, 2018

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Chapter 5 Reading Quiz Question 1

Part A

What is the best description of the term chiral?

Hint 1. Stereochemical jargon

Numerous specific terms are used in stereochemistry. Be sure that you review and understand the meanings of the terms chiral, enantiomer,diastereomer, and meso.

ANSWER:

Correct

Problem 5-3

Using the three-dimensional structure for each compound, determine if there are any asymmetric carbon atoms. Then make the mirror image for each structure,and state whether they are a pair of enantiomers or just the same molecule. Build molecular models of any of these examples that seem difficult to you.

Part A

Check all that apply.

ANSWER:

Correct

Part B


ANSWER:

a structure that can exist as one of several possible stereoisomers

a structure that contains an internal mirror plane of symmetry

a structure that contains a rotational axis of symmetry

a structure that is non-superposable on its mirror image

Has an asymmetric carbon.

No asymmetric carbons.

Mirror image is an enantiomer.

Mirror image is the same molecule.



Correct

Part C


ANSWER:

Correct

Part D

1-bromo-2-methylbutane


ANSWER:

Correct

Part E

chlorocyclohexane


ANSWER:

Correct

Part F



















cis-1,2-dichlorocyclobutane


ANSWER:

Correct

Part G


ANSWER:

Correct

Part H


ANSWER:

Correct

Part I
















ANSWER:

Correct

Problem 5-5

For each compound, determine whether the molecule has an internal mirror plane of symmetry. If the molecule does not have an internal mirror plane,determine whether the structure is chiral.

Part A

methane


ANSWER:

Correct

Part B

cis-1,2-dibromocyclobutane


ANSWER:

Correct

Part C

trans-1,2-dibromocyclobutane


ANSWER:

Correct

Part D





Has a plane of symmetry.

No plane of symmetry.

chiral



chiral



chiral



1,2-dichloropropane


ANSWER:

Correct

Part E


ANSWER:

Correct

Part F


ANSWER:

Correct

Part G


ANSWER:



chiral



chiral



chiral



chiral



Correct

Part H


ANSWER:

Correct

Stereochemistry: Choose the achiral structures

Part A

Choose all the achiral compounds among the ones shown. (Each of your choices can be achiral in any conformation, not just the one shown.)


ANSWER:



chiral



Correct

All of the compounds you chose have a plane of symmetry in at least one conformation. All of the ones you rejected lack a plane of symmetry inevery conformation.

Stereochemistry: Choose the chiral structures

Part A

Choose the chiral structures among the ones shown.


ANSWER:



Correct

None of the compounds you chose has a plane of symmetry. All of the ones you rejected do.

Stereochemistry: Draw all stereoisomers of 2-bromo-4-methylpentane

Part A

Draw all stereoisomers of 2-bromo-4-methylpentane.

Draw the molecules on the canvas by choosing buttons from the Tools (for bonds), Atoms, and Advanced Template toolbars. The single bond isactive by default. Show the appropriate stereochemistry by choosing the dashed or wedged buttons and then clicking a bond on the canvas.

ANSWER:



Correct

There are two stereoisomers of this compound. C(4), to which two CH3 groups are attached, is not a stereocenter. If you put a wedged bondhere, it was ignored.


Part A

What are the absolute configurations of the indicated stereoisomer of 2-bromo-3-methylpentane?

Hint 1. Naming configurations; see 5-3.

Remember that the absolute configurations of asymmetric carbon atoms are specified using the Cahn–Ingold–Prelog convention.

ANSWER:

Correct

Problem 5-6 - Enhanced - with Feedback

You may want to reference (Page) Section 5.3 while completing this problem.

Label each asymmetric carbon atom in the following examples, and identify whether it has the (R) or (S) configuration.

(2S,3R)

(2R,3S)

(2S,3S)

(2R,3R)



Part A

Drag the appropriate labels to their respective targets. Labels can be used once, more than once, or not at all. If the indicated carbon is notasymmetrical, then drag the NA label to that respective target.

ANSWER:

Correct

The central carbon in each molecule is asymmetric as each is bonded to four unique groups. The highest priority attachment in the molecule onthe left is the oxygen (hydroxyl group), then the ethyl group, then the methyl group, and the lowest priority is the hydrogen. When the hydrogen isoriented away from the viewer, the progression is clockwise from the hydroxyl group to the ethyl group to the methyl group, so its designation is(R). The highest priority attachment in the molecule on the right is the bromine, then the ethyl group, then the methyl group, and the lowestpriority is the hydrogen. When the hydrogen is oriented away from the viewer, the progression is counterclockwise from bromine to the ethylgroup to the methyl group, so its designation is (S).

Part B


ANSWER:

HelpReset

R

S

NA

R S



Correct

There is only one asymmetric carbon in the molecule. It is the carbon in the center of the molecule bonded to four different groups. The ethenylgroup has highest priority as a result of the double bond, the isopropyl group is next in priority followed by the methyl group and the lowest priorityis the hydrogen atom. When the hydrogen atom is oriented away from the viewer the progression is clockwise from the ethenyl to the isopropyl tothe hydrogen, so its designation is R.

Part C


ANSWER:

HelpReset

HelpReset

R

S

NAR

NA NANA

RS

NA

S S

NA

NA

NAR

S

NA

NA

NA



Correct

The two molecules are trans-1,2-dichlorocyclopentane (left) and cis-1,2-dichlorocyclopentane (right). Each molecule contains two asymmetriccarbons, which are the ring carbons with the chlorine substituents. The highest priority group on each asymmetric carbon is the chlorine atom,then the adjacent carbon bearing the chlorine atom, then the adjacent carbon without a chlorine substituent, and the lowest priority is thehydrogen atom. If each asymmetric carbon is oriented with the hydrogen facing away from the viewer then the progression of priorities for the twoasymmetric carbons in trans-1,2-dichlorocyclopentane (left) is counterclockwise and counterclockwise, so each of the asymmetric carbons intrans-1,2-dichlorocyclopentane (left) is designated as S. For the cis-1,2-dichlorocyclopentane (right) molecule the progression of priorities for theasymmetric carbon on the left is clockwise, so it is designated as R, and the progression of priorities for the asymmetric carbon on the right iscounterclockwise, so it is designated as S.

Part D


ANSWER:

Correct

Part E


ANSWER:

HelpReset

R

S

NA R

SNA

NA

NA

NA NA

RR

NA

NA

NA

NANA



Incorrect; Try Again; 4 attempts remaining

Part F

Drag the appropriate labels to their respective targets. Labels can be used once, more than once, or not at all. If the indicated carbon is notasymmetrical, then drag the blank label to that respective target.

ANSWER:

Incorrect; Try Again; 3 attempts remaining

Stereochemistry: Draw the structure of (S)-1-bromo-1-chlorobutane

HelpReset

HelpReset

RS

R

R

S

S

S

SS

S



Part A

Draw the structure of (S)-1-bromo-1-chlorobutane. Use bold or hashed wedges to indicate the configuration at stereogenic C atoms.

Draw the molecule on the canvas by choosing buttons from the Tools (for bonds), Atoms, and Advanced Template toolbars. The single bond isactive by default. Show the appropriate stereochemistry by choosing the dashed or wedged buttons and then clicking a bond on the canvas.

ANSWER:

Correct

Chirality

Learning Goal:

To identify chiral molecules, understand optical activity, and draw enantiomers.

Enantiomers are nonsuperimposable mirror images of each other. For example, 2-chlorobutane and its mirror image are optical isomers. Right and left glovesare nonsuperimposable mirror images; thus, they too are enantiomers. A table is an example of anobject that is identical to its mirror image.

Although may see enantiomers referred to as optical isomer, the two are not synonymous. For example,diastereomers are optical isomers but they are not enantiomers.

Chiral molecules

A molecule that contains a carbon that is bonded to four different substituents is chiral. For example, C2 of 2-chlorobutane has four different substituents: , , , and , so 2-chlorobutane is chiral. Molecules that are not chiral are achiral. Chiral molecules are optically active; achiral molecules are

not optically active. Atoms themselves are not chiral, but rather the entire molecule or compound is be chiral.

Part A

Identify which of the following molecules are chiral and which are achiral.

Drag each item to the appropriate bin.

Hint 1. How to approach the problem

Recall the characteristics of chiral molecules. An easy way to determine whether or not a molecule is chiral is to list the substituents of each carbonatom. If a carbon atom has two or more of the same substituent, the resulting molecule is not chiral. If each substituent is different, the resultingmolecule is chiral and the molecule exhibits optical isomerism.Draw each molecule. If any of the carbon atoms have four different groups attached, then the molecule is chiral.

−H−CH3 −Cl −C CH2 H3



Hint 2. Draw butane

Draw butane.

Draw the molecule on the canvas by choosing buttons from the Tools (for bonds), Atoms, and Advanced Template toolbars. The singlebond is active by default.


Butane is an alkane, a hydrocarbon with only single bonds. The prefix but indicates that there are four carbon atoms.

Draw four carbon atoms bonded to each other. Then draw hydrogen atoms bonded to the carbon atoms, remembering that carbon istetravalent and forms four bonds.

ANSWER:

Hint 3. Draw 2-propanol

Draw 2-propanol.



The name 2-propanol gives three important pieces of information about the molecule:

It has three carbon atoms.It is an alcohol.The hydroxyl ( ) group is on C2 (the second carbon atom).

Draw the three carbon atoms. Then draw the hydroxyl group attached to the second (middle) carbon atom. Finally, draw hydrogen atomsbonded to the carbon atoms, remembering that carbon atoms form four bonds.

ANSWER:

−OH



Hint 4. Draw 2-butanol

Draw 2-butanol.



The name 2-butanol gives three important pieces of information about the molecule:

It has four carbon atoms.It is an alcohol.The hydroxyl ( ) group is on C2 (the second carbon atom).

Draw the four carbon atoms. Then draw the hydroxyl group attached to the second carbon atom. Finally, draw hydrogen atoms bonded to thecarbon atoms, remembering that carbon atoms form four bonds.

ANSWER:

−OH



Hint 5. Draw 2-bromobutane

Draw 2-bromobutane.



Butane is an alkane, a hydrocarbon with only single bonds. The prefix but indicates that there are four carbon atoms. The "2-bromo"indicates that there is a bromine atom bonded to the second carbon atom.

ANSWER:



Hint 6. Draw 1-bromobutane

Draw 1-bromobutane.



Butane is an alkane, a hydrocarbon with only single bonds. The prefix but indicates that there are four carbon atoms and "1-bromo" indicatesthat there is a bromine atom bonded to the first carbon atom.

ANSWER:

ANSWER:

Reset Help

2-butanol 2-bromobutanebutane 2-propanol

1-bromobutane

Chiral Achiral



Correct

and are constitutional isomers. Constitutional isomers have the same molecular formula, in thiscase , but the atoms are linked up differently.

does have an enantiomer. Because enantiomers differ only in the arrangement of the atoms about an asymmetric center,the condensed structural formula for its enantiomer is the same, .

Properties of enantiomers

Enantiomers have the same physical and chemical properties. They differ only in the direction they rotate the plane of polarization of plane-polarized light andthey way they react with chiral reagents (such as an enzyme). The levorotatory (-) stereoisomer of an enantiomer pair rotates the plane of polarization polarizedcounterclockwise, whereas the dextrorotatory (+) stereoisomer rotates the plane the same amount, but in a clockwise direction. A racemic mixture is a mixturewith equal amounts of the (-) and (+) isomers.

You may also see the terms l and d used to represent levorotatory and dextrorotatory respectively. These are mainly used in reference to biochemicalmolecules.

Part B

You have a racemic mixture of (+)-2-butanol and (-)-2-butanol. The (+) isomer rotates polarized light by . What is the observed rotation of yourmixture?

Express your answer in degrees.


A racemic mixture contains equal amounts of (+) and (-) isomers. A molecule's (+) isomer rotates polarized light in a clockwise direction. The (-)isomer rotates light in the counterclockwise direction.Determine how (-)-2-butanol rotates polarized light. Then combine this answer with , the rotation of light of (+)-2-butanol.

Hint 2. Determine the rotation of (-)-2 butanol

What is the direction and magnitude of optical rotation for (-)-2-butanol?

Enter the sign (+ or -) and numeric value.

ANSWER:

ANSWER:

Correct

Because enantiomers rotate the plane of polarization of plane-polarized light in equal and opposite directions, a racemic mixture—that is, amixture containing equimolar amounts of the two stereoisomers—will not rotate the plane of polarization of plane-polarized light. That is, aracemic mixture is optically inactive.

Part C

Two products, structural isomers of each other, are possible for the bromination of butane via the reaction

One of these products exhibits optical isomerism. Draw this product. Assume mono substitution.

Draw the molecule on the canvas by choosing buttons from the Tools (for bonds), Atoms, and Advanced Template toolbars. The single bond isactive by default.


The halogenation of an alkane results in the substitution of the halogen (for example, chlorine or bromine) for one or more hydrogen atoms. Thisquestion specifies mono substitution, so one bromine atom will substitute for one of the hydrogen atoms.Determine the two possible products. These products are structural isomers. Then identify which of the products is chiral. Finally, draw the chiralproduct.

Hint 2. Predict the two possible products

Choose the product(s) of the bromination of butane (assuming mono substitution).


ANSWER:

C C CHBrCH3 H2 H3 C C C C BrH3 H2 H2 H2

BrC4H9

C C CHBrCH3 H2 H3

C C CHBrCH3 H2 H3

+13.5∘

+13.5∘

-13.5 ∘

0 ∘

C C C CH3 H2 H2 H3 + Br2 ⟶

heat or light

?



Hint 3. Identify the chiral molecule

Given the condensed structural formulas for the two products of the bromination of butane, choose the chiral molecule.

ANSWER:

ANSWER:

Correct

2-Bromobutane is represented by two optical isomers, a d (dextrorotatory) isomer and an l (levorotatory) isomer. These isomers are mirrorimages of each other, but they cannot be superimposed on each other because of the tetrahedral arrangement of the carbon atom's four bonds.

Notice the image in the introduction of the similarly arranged molecule 2-chlorobutane.

Stereochemistry: Draw the product of (S)-(+)-1-chloro-2-methylbutane and chlorine with the correctsterochemistry

Part A

When (S)-(+)-1-chloro-2-methylbutane reacts with chlorine, one of the products formed is (-)-1,4-dichloro-2-methylbutane. Draw the product with theconfiguration indicated correctly.

C C C CH3 H2 H2 H3

C CHBrC CH3 H2 H3

C C C C BrH3 H2 H2 H2

C CHBrCHBrCH3 H3

C CBrC CH3 H2 H3

C BrCHBrC CH2 H2 H3

C CHBrC CH3 H2 H3

C C C C BrH3 H2 H2 H2



Interactive 3D display mode

Draw the molecule on the canvas by choosing buttons from the Tools (for bonds), Atoms, and Advanced Template toolbars. The single bond isactive by default. Show the appropriate stereochemistry by choosing the dashed or wedged buttons and then clicking a bond on the canvas.

ANSWER:

Correct

Excellent! When the substrate undergoes this reaction, no bonds to the stereogenic C atom are broken, so its configuration remains unchanged.The change in the direction of the optical rotation is irrelevant.

Stereochemistry: Determine the relationship between the two structures (I)

Part A

Choose the term that best describes the relationship between the two structures.

ANSWER:



Correct

The only difference is in the location of bonds.


Part A

How many stereoisomers are possible for the following structure?

Hint 1. Stereoisogenic centers

A stereogenic atom is defined as an atom at which the exchange of two groups gives a stereoisomer. A molecule can have as many as 2n

stereoisomers, where n is equal to the number of stereogenic atoms present. See 5-11.

ANSWER:

Correct

Problem 5-22

Using the drawings of all the distinct stereoisomers for each structure, identify the relationships (enantiomers, diastereomers, etc.) between the isomers.

Part A

Drag the appropriate items to their respective bins.

ANSWER:

configurational enantiomers

conformational diastereomers

resonance structures

skeletal isomers

configurational diastereomers

conformational enantiomers

homomers

neither isomers, nor resonance structures, nor homomers

π

1

2

4

8

C −CHCl−CHOH−COOHH3



Correct

Part B

tartaric acid,


ANSWER:

Correct

Reset Help

HOOC−CHOH−CHOH−COOH

Reset Help

A and B C and D B and D A and C B and C A and D

F and G E and G E and F

enantiomers diastereomers




Part C

Which of the following structures of are enantiomers?


ANSWER:

Correct

Part D


ANSWER:

HOOC−CHBr−CHOH−CHOH−COOH

I and M

H and L

L and M

H and I

K and O

J and K

L and O

H and K

J and N

N and O



Correct

Part E


ANSWER:

Reset Help

Q and R P and R P and Q




Correct

Score Summary:Your score on this assignment is 91.2%.

You received 12.77 out of a possible total of 14 points.

Reset Help

S and T T and V T and U S and U S and V U and V


Documents

Problem 5-3€¦ · the left is the oxygen (hydroxyl group), then the ethyl group, then the methyl group, and the lowest priority is the hydrogen. When the hydrogen is oriented away