Organic Chemistry

Janice Gorzynski Smith

Chapter 8

Alkyl Halides and Elimination Reactions - all with Video Answers

Educators

Chapter Questions

Problem 1

Label the $\alpha$ and $\beta$ carbons in each alkyl halide. Draw all possible elimination products formed when each alkyl halide is treated with $\mathrm{K}^{+-} \mathrm{OC}\left(\mathrm{CH}_{3}\right)_{3}$.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 2

Classify each alkene in the following vitamins by the number of carbon substituents bonded to the double bond.

Prashant Singh

Numerade Educator

Problem 3

For which double bonds are stereoisomers possible?

Christopher Peters

Christopher Peters

Numerade Educator

Problem 4

(a) Which double bonds in (E)-ocimene, a major component of the odor of lilac flowers, can exhibit stereoisomerism? (b) Draw a diastereomer of (E)-ocimene.

Prashant Singh

Numerade Educator

Problem 5

Label each pair of alkenes as constitutional isomers, stereoisomers, or identical.

Chloe Schroeder

Chloe Schroeder

Numerade Educator

Problem 6

Which alkene in each pair is more stable?

Prashant Singh

Numerade Educator

Problem 7

Rank the following alkenes in order of increasing stability.

Christopher Peters

Christopher Peters

Numerade Educator

Problem 8

Use curved arrows to show the movement of electrons in the following E2 mechanism. Draw the structure of the transition state.

Prashant Singh

Numerade Educator

Problem 9

Consider an E2 reaction between $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br}$ and $\mathrm{KOC}\left(\mathrm{CH}_{3}\right)_{3} .$ What effect does each of the following changes have on the rate of elimination? (a) The base is changed to KOH. (b) The alkyl halide is changed to $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl} .$

Christopher Peters

Christopher Peters

Numerade Educator

Problem 10

Rank the alkyl halides in each group in order of increasing reactivity in an E2 reaction.

Prashant Singh

Numerade Educator

Problem 11

How does each of the following changes affect the rate of an E2 reaction?
a. tripling [RX]
b. halving [B:]
c. changing the solvent from $\mathrm{CH}_{3} \mathrm{OH}$ to DMSO
d. changing the leaving group from $I^{-}$ to $B r^{-}$
e. changing the base from ${ }^{-} \mathrm{OH}$ to $\mathrm{H}_{2} \mathrm{O}$
f. changing the alkyl halide from $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br}$ to $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHBr}$

Christopher Peters

Christopher Peters

Numerade Educator

Problem 12

What alkenes are formed from each alkyl halide by an E2 reaction? Use the Zaitsev rule to predict the major product.

Prashant Singh

Numerade Educator

Problem 13

Draw an E1 mechanism for the following reaction. Draw the structure of the transition state for each step.

Christopher Peters

Christopher Peters

Numerade Educator

Problem 14

What alkenes are formed from each alkyl halide by an E1 reaction? Use the Zaitsev rule to predict the major product.

Prashant Singh

Numerade Educator

Problem 15

How does each of the following changes affect the rate of an E1 reaction?
a. doubling [RX]
b. doubling [B:]
c. changing the halide from $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CBr}$ to $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}$
d. changing the leaving group from $\mathrm{Cl}^{-}$ to $\mathrm{Br}^{-}$
e. changing the solvent from DMSO to $\mathrm{CH}_{3} \mathrm{OH}$

Christopher Peters

Christopher Peters

Numerade Educator

Problem 16

Draw both the $S_{N} 1$ and E1 products of each reaction.

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 17

Given that an E2 reaction proceeds with anti periplanar stereochemistry, draw the products of each elimination. The alkyl halides in (a) and (b) are diastereomers of each other. How are the products of these two reactions related? Recall from Section $3.2 \mathrm{~A}$ that $\mathrm{C}_{6} \mathrm{H}_{5}-$ is a phenyl group, a benzene ring bonded to another group.

Prashant Singh

Numerade Educator

Problem 18

Draw the major E2 elimination products from each of the following alkyl halides.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 19

Explain why cis-1-chloro-2-methylcyclohexane undergoes E2 elimination much faster than its trans isomer.

Prashant Singh

Numerade Educator

Problem 20

Which mechanism, E1 or E2, will occur in each reaction?

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 21

Draw the alkynes formed when each dihalide is treated with excess base.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 22

Draw the products in each reaction.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 23

Draw a stepwise mechanism for the following reaction.

Colton K

Numerade Educator

Problem 24

Rank the alkenes shown in the ball-and-stick models (A-C) in order of increasing stability.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 25

Name each compound and decide which stereoisomer will react faster in an E2 elimination reaction. Explain your choice.

Prashant Singh

Numerade Educator

Problem 26

What is the major E2 elimination product formed from each alkyl halide?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 27

Draw all possible constitutional isomers formed by dehydrohalogenation of each alkyl halide.

Prashant Singh

Numerade Educator

Problem 28

What alkyl halide forms each of the following alkenes as the only product in an elimination reaction?

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 29

Which double bonds in the following natural products can exhibit stereoisomerism? Nerolidol is isolated from the angel's trumpet plant, caryophyllene is present in hemp, and humulene comes from hops.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 30

Label each pair of alkenes as constitutional isomers, stereoisomers, or identical.

Chloe Schroeder

Chloe Schroeder

Numerade Educator

Problem 31

Rank the following alkenes in order of increasing stability.

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 32

$\Delta H^{\circ}$ values obtained for a series of similar reactions are one set of experimental data used to determine the relative stability of alkenes. Explain how the following data suggest that cis-but-2-ene is more stable than but-1-ene (Section $12.3 \mathrm{~A}$ ).

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 33

Draw all constitutional isomers formed in each E2 reaction, and predict the major product using the Zaitsev rule.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 34

For each of the following alkenes, draw the structure of two different alkyl halides that yield the given alkene as the only product of dehydrohalogenation.

Prashant Singh

Numerade Educator

Problem 35

Consider the following E2 reaction.
a. Draw the by-products of the reaction and use curved arrows to show the movement of electrons.
b. What happens to the reaction rate with each of the following changes? [1] The solvent is changed to DMF. [2] The concentration of $^{-} \mathrm{OC}\left(\mathrm{CH}_{3}\right)_{3}$ is decreased. [3] The base is changed to -OH. [4] The halide is changed to $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_{3} .$ [5] The leaving group is changed to I'.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 36

What is the major stereoisomer formed when each alkyl halide is treated with $\mathrm{KOC}\left(\mathrm{CH}_{3}\right)_{3} ?$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 37

What alkene is the major product formed from each alkyl halide in an E1 reaction?

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 38

Rank the following alkyl halides in order of increasing reactivity in E2 elimination. Then do the same for E1 elimination.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 39

Draw all constitutional isomers formed in each elimination reaction. Label the mechanism as E2 or E1.

Prashant Singh

Numerade Educator

Problem 40

In the dehydrohalogenation of bromocyclodecane, the major product is cis-cyclodecene rather than trans-cyclodecene. Offer an explanation.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 41

What is the major E2 elimination product formed from each halide?

Prashant Singh

Numerade Educator

Problem 42

Taking into account anti periplanar geometry, predict the major E2 product formed from each starting material.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 43

Does cis- or trans-1-bromo-4-tert-butylcylohexane react faster in an E2 reaction?

Andrew Lee

Numerade Educator

Problem 44

a. Draw three-dimensional representations for all stereoisomers of 2chloro-3-methylpentane, and label pairs of enantiomers.
b. Considering dehydrohalogenation across only $\mathrm{C} 2$ and $\mathrm{C} 3$, draw the E2 product that results from each of these alkyl halides. How many different products have you drawn?
c. How are these products related to each other?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 45

Which of the following compounds undergoes E2 elimination with strong base? For compounds that undergo elimination, draw the product. For compounds that do not undergo elimination, explain why they are unreactive.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 46

Draw the structure (including stereochemistry) of an alkyl chloride that forms each alkene as the exclusive E2 elimination product.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 47

Draw the major stereoisomer formed when each compound is treated with NaOH.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 48

Draw the products formed when each dihalide is treated with excess $\mathrm{NaNH}_{2}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 49

Draw the structure of a dihalide that could be used to prepare each alkyne. There may be more than one possible dihalide.

Prashant Singh

Numerade Educator

Problem 50

Under certain reaction conditions, 2,3 -dibromobutane reacts with two equivalents of base to give three products, each of which contains two new $\pi$ bonds. Product A has two sp hybridized carbon atoms, product B has one $s p$ hybridized carbon atom, and product $C$ has none. What are the structures of $\mathrm{A}, \mathrm{B},$ and $\mathrm{C}$ ?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 51

For which reaction mechanisms-s $_{\mathrm{N}} 1, \mathrm{~S}_{\mathrm{N}} 2, \mathrm{E} 1,$ or $\mathrm{E} 2-$ are each of the following statements true? A statement may be true for one or more mechanisms.
a. The mechanism involves carbocation intermediates.
b. The mechanism has two steps.
c. The reaction rate increases with better leaving groups.
d. The reaction rate increases when the solvent is changed from $\mathrm{CH}_{3} \mathrm{OH}$ to $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{SO} .$
e. The reaction rate depends on the concentration of only the alkyl halide.
f. The mechanism is concerted.
g. The reaction of $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br}$ with NaOH occurs by this mechanism.
h. Racemization at a stereogenic center occurs.
i. Tertiary $\left(3^{\circ}\right)$ alkyl halides react faster than $2^{\circ}$ or $1^{\circ}$ alkyl halides.
j. The reaction follows a second-order rate equation.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 52

Draw the organic products formed in each reaction.

Ian Kaigh

Numerade Educator

Problem 53

What reagents and reaction conditions are needed for each of the following conversions?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 54

Draw all products, including stereoisomers, in each reaction.

Prashant Singh

Numerade Educator

Problem 55

Draw all of the substitution and elimination products formed from the given alkyl halide with each reagent: (a) $\mathrm{CH}_{3} \mathrm{OH} ;$ (b) KOH. Indicate the stereochemistry around the stereogenic centers present in the products, as well as the mechanism by which each product is formed.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 56

The following reactions do not afford the major product that is given. Explain why this is so, and draw the structure of the major product actually formed.

Prashant Singh

Numerade Educator

Problem 57

Draw a stepwise, detailed mechanism for each reaction.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 58

Draw the major product formed when (R)-1-chloro-3-methylpentane is treated with each reagent: (a) $\mathrm{NaOCH}_{2} \mathrm{CH}_{3} ;$ (b) KCN; (c) DBU.

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 59

Draw a stepwise, detailed mechanism for the following reaction.

Ian Kaigh

Numerade Educator

Problem 60

Explain why the reaction of 2 -bromopropane with $\mathrm{NaOCOCH}_{3}$ gives $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOCOCH}_{3}$ exclusively as product, but the reaction of $2-$ bromopropane with $\mathrm{NaOCH}_{2} \mathrm{CH}_{3}$ gives a mixture of $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOCH}_{2} \mathrm{CH}_{3}$
$(20 \%)$ and $\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}(80 \%)$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 61

Explain why alkene $A$ is more stable than alkene $B$, even though $B$ contains more carbon atoms bonded to the double bond. Would you expect $C$ to be more or less stable than $A$ and $B$ ?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 62

Draw a stepwise detailed mechanism that illustrates how four organic products are formed in the following reaction.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 63

Although there are nine stereoisomers of $1,2,3,4,5,6-$ hexachlorocyclohexane, one stereoisomer reacts 7000 times more slowly than any of the others in an E2 elimination. Draw the structure of this isomer and explain why this is so.

Prashant Singh

Numerade Educator

Problem 64

Explain the selectivity observed in the following reactions.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 65

Draw a stepwise mechanism for the following reaction. The fourmembered ring in the starting material and product is called a $\beta$ -lactam. This functional group confers biological activity on penicillin and many related antibiotics, as is discussed in Chapter $20 .$ (Hint: The mechanism begins with $\beta$ elimination and involves only two steps.)

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 66

Although dehydrohalogenation occurs with anti periplanar geometry, some eliminations have syn periplanar geometry. Examine the starting material and product of each elimination, and state whether the elimination occurs with syn or anti periplanar geometry.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 67

(a) Draw all products formed by treatment of each dibromide (A and B) with one equivalent of NaNH $_{2}$. (b) Label pairs of diastereomers and constitutional isomers.

Prashant Singh

Numerade Educator