Chapter 5 Homework Solutions 2 PDF

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Mission College CHEM-012A Dr. Baker Answers for Chapter 6 – Alkenes: Structure and Reactivity Calculate the degree of unsaturation in each formula below. Show your calculations. Q1. Pinene, ! C10 H18 Answer: The saturated ten carbon compound would have 22 hydrogens so the number of degrees of ( ) un...

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Mission College CHEM-012A Dr. Baker Answers for Chapter 6 – Alkenes: Structure and Reactivity Calculate the degree of unsaturation in each formula below. Show your calculations. Q1. Pinene, ! C10 H18 Answer: The saturated ten carbon compound would have 22 hydrogens so the number of degrees of ( )÷ = ÷ = unsaturation is: ! 22 − 18 2 4 2 2 Q2.

3.

Eicosapentaenoic acid, C20H30O2, a constituent of fish oil Answer: Oxygen does not affect the base formula which in this case is C20H30. The saturated 20 carbon compound would have 42 hydrogens so the number of degrees of unsaturation for eiscosapentaenoic acid is: (42 – 30) ÷ 2 = 12 ÷ 2 = 6. C H N OCl Diazepam (Valium), ! 16 13 2 Answer: Oxygen does not affect the base formula. A hydrogen is added to the base formula for each halogen and subtracted for each nitrogen so the base formula for diazepam is . The saturated 16 carbon compound would have 34 hydrogens so the number of degrees of unsaturation for diazepam is: (34 -- 12) / 2 = 22 / 2 = 11.

Dieldrin, C12H8Cl6O, is a pentacyclic compound formerly used as an insecticide. Q4. Calculate the degree of unsaturation for Dieldrin. Show calculations for credit. Answer: Oxygen does not affect the base formula. A hydrogen is added to the base formula for each halogen so the base formula for dieldrin is C12H14. The saturated 12 carbon compound would have 26 hydrogens so the number of degrees of unsaturation for dieldrin is (26 -- 14) / 2 = 12 / 2 = 6. 5.

How many double bonds does dieldrin have? Answer: Dieldrin has 6 degrees of unsaturation and it is pentacyclic, meaning it has 5 rings. Therefore, dieldrin must have one double bond.

Draw structures corresponding to each name below. Either condensed or line structures may be used. 6. Answer: (CH3)2C

CH3

CHCH2

or

C

C

H

CH

CH2

7. Answer: CH3

or

8.

cis-2Answer:

hexene

CH3

H3C or

CH2CH2CH3 C

H

Q9.

trans-4,4-dimethyl-2-pentene Answer: H3C

H C

or H

C C(CH3)2CH3

C H

2-Pentene is an example of a disubstituted alkene.

CH3CH

CHCH2CH3

Q10.

Draw the cis and trans isomers of 2-pentene and label them. Answer:

Q11.

Circle the isomer which is most stable. H3C

H3C

CH2CH3 C

H

C

H H3C

C H CH2CH3

cis C

CH H 2CH3

H3C H

trans C C

C

H

C

H

CH2CH3

H

cis

trans

Answer: Provide names for each structure below. Be sure to include the cis, trans or E, Z designations where applicable. Q12.

Answer: trans-2-methyl-3-hexene or (E)-2-methyl-3-hexene Q13.

Answer: 3-methylcyclopentene Q14.

Q15.

CH2CH2CH3 H2C

CH2CH3

CHC(CH3)2CH C

C

H

H

Answer: cis-3,3-dimethyl-4-propyl-1,5-octadiene or (Z)-3,3-dimethyl-4-propyl-1,5-octadiene Rank each set of substituents using the Cahn-Ingold-Prelog sequence rules by numbering the highest priority substituent 1 and numbering the lowest priority substituent 4. Place the number in the blank below the substituent. Q16. CH CH CH 2

H2C

2

CHC(CH3)2CH C

C

H

Answer:

3

CH2CH3 H

O C

H

CH

1

Q17.

CHCH3 4

NCH3 2

O NHCCH3

CH

C

H

CH

C

CH3

3

CH3

CH3 C

C

CH3

CH

OH

Answer: O

CH3

CH3 C

NHCCH3 1

C

H

CH

CH

CH3

4

3

Q18.

OH

2

O CH2

C

I

N

OH

C

OCH3

CH

CHCH3

Answer: O CH2

I

1

Q19.

C

N

OH

3

CH2 OH

C

C

OCH3

CH

2

N

CH2

CHCH3

4

Cl

CH

CH2

Answer: CH2 OH

C

N

3

2

CH2 1

Cl

CH

CH2

4

MATCH each alkene below with the appropriate heat of hydrogenation. Place the letter of the correct answer in the blank to the left of the alkene. a. 125.9 kJ/mol Q20.

H3C

H

b. 118.4 kJ/mol

c. 115.5 kJ/mol

H

CH3

Answer: c Q21.

H

H

H

CH3

Answer: a Q22.

H3C

H Answer: b 23.

CH2CH3

H

Arrange the following bicyclic alkenes in order of increasing stability (least stable to most stable).

II

I

a.

III < II < I

b.

III

I < II < III

c.

I < III < II

d.

II < III < I

Answer: d Assign E or Z configurations to each alkene below. H3C

CH3

Q24. Br

CH2CH3

Answer: Z CN

Q25.

CH2CH2OH

CH3

Answer: E Q26.

O H3COC

O

C

CH3 C

CH2

C

CH

OH

Answer: E MATCH each definition to the term it describes. Place the letter corresponding to the term in the blank to the left of the definition. a. Hammond Postulate

b. Cahn-Ingold-Prelog Rules

c. Markovnikov’s Rule

Q27.

Predicts that the more stable carbocation intermediate is formed in electrophilic additions to alkenes. Answer: c

Q28.

Predicts that the transition state of an exergonic reaction step structurally resembles the reactant. Answer: a

Q29.

Assigns priorities to the substituent groups on a carbon. Answer: b

Q30.

Predicts that the transition state of an endergonic reaction step structurally resembles the product. Answer: a

Q31.

_____ Predicts that in additions of HX to alkenes, the H adds to the less substituted alkene carbon and the X adds to the more substituted alkene carbon. Answer: c

Q32.

Rank the carbocations below in order of increasing stability (least stable = 1; most stable = 3). Place the number corresponding to the carbocation’s relative stability in the blank below the structure. + + +

Answer: + + + 3

1

2

Consider the following reaction: CH3

CH3 +

Q33.

HCl

Cl

Write the complete stepwise mechanism for this reaction. Show all intermediate structures and show all electron flow using the curved arrow convention. Answer: CH3 H

+

Cl

_ Cl

H H

Q34.

CH3

CH3

Cl

H

Draw a qualitative reaction energy diagram for this reaction. Label the positions of all reactants, intermediates and products. Answer:

first TS second TS =/ ΔG1

Energy

=/ ΔG2 intermediate

reactants ΔG0 products

Reaction Progress

Consider the following reaction: Cl (CH3)3CCH

Q35.

CH2

+

(CH3)3CCHCH3

HCl

+

(CH3)2CCHCH3

Cl

CH3

A 50%

B 50%

Below are all the chemical structures and intermediates involved in this reaction. On the structures provided, show all electron flow using the arrow formalism for the complete stepwise mechanism for this reaction. _ Cl

Pathway A

(CH3)3CCH

CH2

H

Cl

(CH3)3CCH +

CH3

(CH3)3CCHCH3 Cl

Pathway B

A

CH3 (CH3)2C

CH3 CH +

CH3

(CH3)2C +

CH

_ CH3

Cl

Cl (CH3)2CCHCH3 CH3 B

Answer: _

Pathway A

(CH3)3CCH

H

CH2

Cl

(CH3)3CCH +

(CH3)3CCHCH3

Cl

CH3

Cl Pathway B

A CH3

CH3 (CH3)2C

CH +

CH3

(CH3)2C +

CH

Cl

_ CH3

(CH3)2CCHCH3

Cl

CH3 B

Q36.

Why does the rearrangement that results in the formation of product B occur? Answer: The 1,2-alkyl shift is the rearrangement of a secondary carbocation to a more stable tertiary carbocation.

Q37.

Write the complete stepwise mechanism for the following reaction. Show all intermediate structures and all electron flow with arrows. H3C

H3C

CH3

Br CH3

HBr

Answer: Predict the major organic product for each reaction below. Q38.

CH3

H3C

HI3 CH

H3C

H

_

+

Br

+ H

Answer: CH3

H3C

I

HI

Q39.

HCl ether

Answer: HCl ether Cl

Q40.

HBr

Answer: Br HBr

CH3

CH3 Br

+

H3C CH3

_ Br

Br CH3

Q41.

KI H3PO4

Answer:

I KI H3PO4

Predict the structure of the alkene you would use to prepare each alkyl halide below. Br

Q42. (only product)

Answer:

Q43. Answer: I

I

CH3CHCH2CHCH3

The reaction of isobutene with HBr in ether gives one of the two products below as the major product. Answer the following questions about this reaction. Br HBr

Br

+

ether Product A

!

Product B

Q44.

Which product would be the major product? Answer: Product B

Q45.

Which product would be formed via a primary carbocation? Answer: Product A

Q46.

Which product would have a higher energy transition state for the formation of the intermediate leading to it? Answer: Product A

Q47.

Which product is the non-Markovnikov product? Answer: Product A

Q48.

According to Hammond’s Postulate, which product would have a transition state structure most closely resembling the carbocation intermediate? Answer: Product A

Q49.

Which product would be formed by a carbocation experiencing the greatest degree of hyperconjugative stabilization? Answer: Product B

Q50.

Increasing the temperature at which the reaction is run would lead to an increase in the percentage of which product relative to the other product? Answer: Product A...