Organic Chemistry

John McMurry

Chapter 11

Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations - all with Video Answers

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Chapter Questions

Problem 1

What product would you expect from a nucleophilic substitution reaction of
(S)-2-bromohexane with acetate ion, $\mathrm{CH}_{3} \mathrm{CO}_{2}^{-}$ ? Assume that inversion of configuration occurs, and show the stereochemistry of both the reactant and product.

Osman Elomda

Osman Elomda

Numerade Educator

Problem 2

What product would you expect to obtain from $\mathrm{S}_{\mathrm{N}}^{2 \text { reaction of } \mathrm{OH}^{-}}$ with $(R)-2$ bromobutane? Show the stereochemistry of both the reactant and product.

Osman Elomda

Numerade Educator

Problem 3

Assign configuration to the following substance, and draw the structure of the product that would result from nucleophilic substitution reaction with $\mathrm{HS}^{-}$ (reddish brown $=\mathrm{Br})$

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 4

What product would you expect from $\mathrm{S}_{\mathrm{N}} 2$ reaction of 1 -bromobutane with each of the following?
(a) NaI
(b) $\mathrm{KOH}$
(c) $\mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{Li}$
(d) $\mathrm{NH}_{3}$

Alma Victoriano

Alma Victoriano

North Carolina State University

Problem 5

Which substance in each of the following pairs is more reactive as a nucleophile? Explain.
(a) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{~N}^{-}$ or $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}$
(b) $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~B}$ or $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}$
(c) $\mathrm{H}_{2} \mathrm{O}$ or $\mathrm{H}_{2} \mathrm{~S}$

Alma Victoriano

Alma Victoriano

North Carolina State University

Problem 6

Rank the following compounds in order of their expected reactivity toward $\mathrm{S}_{\mathrm{N}}^{2}$ reaction:
$$
\mathrm{CH}_{3} \mathrm{Br}, \mathrm{CH}_{3} \mathrm{OTos},\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCl},\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCl}
$$

Osman Elomda

Numerade Educator

Problem 7

Organic solvents like benzene, ether, and chloroform are neither protic nor strongly polar. What effect would you expect these solvents to have on the reactivity of a nucleophile in $\mathrm{S}_{\mathrm{N}} 2$ reactions?

Alma Victoriano

Alma Victoriano

North Carolina State University

Problem 8

What product(s) would you expect from reaction of ( $S$ )- 3 -chloro-3-methyloctane with acetic acid? Show the stereochemistry of both reactant and product.

Alma Victoriano

Alma Victoriano

North Carolina State University

Problem 9

Among the many examples of $\mathrm{S}_{\mathrm{N}} 1$ reactions that occur with incomplete racemization, the optically pure tosylate of 2,2 -dimethyl-1-phenyl-1-propanol $\left([\alpha]_{D}=-30.3\right)$ gives the corresponding acetate $\left([\alpha]_{D}=+5.3\right)$ when heated in acetic acid. If complete inversion had occurred, the optically pure acetate would have had $[\alpha]_{\mathrm{D}}=+53.6 .$ What percentage racemization and what percentage inversion occurred in this reaction?

Osman Elomda

Numerade Educator

Problem 10

Assign configuration to the following substrate, and show the stereochemistry and identity of the product you would obtain by $\mathrm{S}_{\mathrm{N}} 1$ reaction with water (reddish brown $=\mathrm{Br}$ ):

Osman Elomda

Numerade Educator

Problem 11

Rank the following substances in order of their expected SN1 reactivity:

Osman Elomda

Numerade Educator

Problem 12

3-Bromo-1-butene and 1 -bromo-2-butene undergo $\mathrm{S}_{\mathrm{N}} 1$ reaction at nearly the same rate, even though one is a secondary halide and the other is primary. Explain.

Alma Victoriano

Alma Victoriano

North Carolina State University

Problem 13

Predict whether each of the following substitution reactions is likely to be $\mathrm{S}_{\mathrm{N}} 1$ or $\mathrm{S}_{\mathrm{N}} 2$
(a)

Osman Elomda

Numerade Educator

Problem 14

Review the mechanism of geraniol biosynthesis shown in Figure $11-15,$ and propose a mechanism for the biosynthesis of limonene from linalyl diphosphate.

Lainey Roebuck

Numerade Educator

Problem 15

Ignoring double-bond stereochemistry, what products would you expect from elimination reactions of the following alkyl halides? Which product will be the major product in each case?
(a)
(b)
(c)

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 16

What alkyl halides might the following alkenes have been made from?
(a)
(b)

Osman Elomda

Numerade Educator

Problem 17

What stereochemistry do you expect for the alkene obtained by E2 elimination of $(1 R, 2 R)-1,2$ -dibromo- 1,2 -diphenylethane? Draw a Newman projection of the reacting conformation.

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 18

What stereochemistry do you expect for the trisubstituted alkene obtained by E2 elimination of the following alkyl halide on treatment with KOH? (Reddish brown $=\mathrm{Br} .)$

Lainey Roebuck

Numerade Educator

Problem 19

Which isomer would you expect to undergo E2 elimination faster, trans-1-bromo4-tert-butylcyclohexane or cis-1-bromo-4-tert-butylcyclohexane? Draw each molecule in its more stable chair conformation, and explain your answer.

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 20

Tell whether each of the following reactions is likely to be $\mathrm{S}_{\mathrm{N}} 1, \mathrm{~S}_{\mathrm{N}} 2, \mathrm{E} 1, \mathrm{E} 1 \mathrm{cB}$ or E2:
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br} \quad \frac{\mathrm{NaN}_{3}}{\mathrm{THF}} \quad \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{~N}=\mathrm{N}=\mathrm{N}$
(b)
(c)
(d)

Osman Elomda

Numerade Educator

Problem 21

Write the product you would expect from reaction of each of the following alkyl halides with (1) $\mathrm{Na}^{+-} \mathrm{SCH}_{3}$ and (2) $\mathrm{Na}^{+-} \mathrm{OH}$ (green $=\mathrm{Cl}$ ):
(a)
(b)
(c)

Lainey Roebuck

Numerade Educator

Problem 22

From what alkyl bromide was the following alkyl acetate made by $\mathrm{S}_{\mathrm{N}}$ 2 reaction? Write the reaction, showing all stereochemistry.

Lainey Roebuck

Numerade Educator

Problem 23

Assign $R$ or $S$ configuration to the following molecule, write the product you would expect from $\mathrm{S}_{\mathrm{N}} 2$ reaction with $\mathrm{NaCN}$, and assign $R$ or $S$ configuration to the product (green $=\mathrm{Cl}$ ):

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 24

Draw the structure and assign $Z$ or $E$ stereochemistry to the product you expect from $\mathrm{E} 2$ reaction of the following molecule with $\mathrm{NaOH}$ (green $=\mathrm{Cl}$ ):

Osman Elomda

Numerade Educator

Problem 25

Predict the product(s) and show the mechanism for each reaction below. What do the mechanisms have in common? Why?
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{O}$ Tos $+\mathrm{NaBr} \quad \overline{\mathrm{DMF}}$
(c)

Lainey Roebuck

Numerade Educator

Problem 26

Show the mechanism for each reaction below. What do the mechanisms have in common? Why?
(a)
(b)
(c)

Lainey Roebuck

Numerade Educator

Problem 27

Predict the product(s) for each elimination reaction below. In each case show the mechanism. What do the mechanisms have in common? Why?

Anand Jangid

Numerade Educator

Problem 28

Predict the product(s) for each elimination reaction below. In each case show the mechanism. What do the mechanisms have in common? Why?
\begin{tabular}{l}
(a) \\
\hline
\end{tabular}
(c)

Lainey Roebuck

Numerade Educator

Problem 29

Predict the product(s) for each elimination reaction below. In each case show the mechanism. What do the mechanisms have in common? Why?
(a)
(b)
(c)

Lainey Roebuck

Numerade Educator

Problem 30

Predict the product of each reaction below and indicate if the mechanism is likely to be $\mathrm{S}_{\mathrm{N}} 1, \mathrm{~S}_{\mathrm{N}} \mathrm{2}, \mathrm{E} 1, \mathrm{E} 2,$ or $\mathrm{E} 1 \mathrm{cB} .$
(a)
(b)
(c)
(d)

Madi Sousa

Numerade Educator

Problem 31

We saw in Section 8 - 7 that bromohydrins are converted into epoxides when treated with base. Propose a mechanism, using curved arrows to show the electron flow.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 32

The following tertiary alkyl bromide does not undergo a nucleophilic substitution reaction by either $\mathrm{S}_{\mathrm{N}} 1$ or $\mathrm{S}_{\mathrm{N}}^{2}$ mechanisms. Explain.

Osman Elomda

Numerade Educator

Problem 33

Metabolism of S-adenosylhomocysteine (Section $11-6$ ) involves the following sequence. Propose a mechanism for the second step.

Lainey Roebuck

Numerade Educator

Problem 34

Reaction of iodoethane with CN $^{-}$ yields a small amount of isonitrile, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{~N} \equiv \mathrm{C},$ along with the nitrile $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{C}=\mathrm{N}$ as the major prod-
uct. Write electron-dot structures for both products, assign formal charges as necessary, and propose mechanisms to account for their formation.

Lainey Roebuck

Numerade Educator

Problem 35

One step in the urea cycle for ridding the body of ammonia is the conversion of argininosuccinate to the amino acid arginine plus fumarate. Propose a mechanism for the reaction, and show the structure of arginine.

Anand Jangid

Numerade Educator

Problem 36

Methyl esters $\left(\mathrm{RCO}_{2} \mathrm{CH}_{3}\right)$ undergo a cleavage reaction to yield carboxylate ions plus iodomethane on heating with LiI in dimethylformamide:
The following evidence has been obtained: (1) The reaction occurs much faster in DMF than in ethanol. (2) The corresponding ethyl ester $\left(\mathrm{RCO}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\right)$ cleaves approximately 10 times more slowly than the methyl ester. Propose a mechanism for the reaction. What other kinds of experimental evidence could you gather to support your hypothesis?

Lainey Roebuck

Numerade Educator

Problem 37

$\quad \mathrm{S}_{\mathrm{N}} 2$ reactions take place with inversion of configuration, and $\mathrm{S}_{\mathrm{N}} 1$ reactions take place with racemization. The following substitution reaction, however, occurs with complete retention of configuration. Propose a mechanism.

Lainey Roebuck

Numerade Educator

Problem 38

Propose a mechanism for the following reaction, an important step in the laboratory synthesis of proteins:

Lainey Roebuck

Numerade Educator

Problem 39

Draw all isomers of $\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{Br}$, name them, and arrange them in order of decreasing reactivity in the $\mathrm{S}_{\mathrm{N}}^{2}$ reaction.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 40

The following Walden cycle has been carried out. Explain the results, and indicate where Walden inversion occurs.

Lainey Roebuck

Numerade Educator

Problem 41

Which compound in each of the following pairs will react faster in an $\mathrm{S}_{\mathrm{N}}^{2}$ reaction with $\mathrm{OH}^{-} ?$
(a) $\mathrm{CH}_{3} \mathrm{Br}$ or $\mathrm{CH}_{3} \mathrm{I}$
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{I}$ in ethanol or in dimethyl sulfoxide
(c) $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCl}$ or $\mathrm{CH}_{3} \mathrm{Cl}$
(d) $\mathrm{H}_{2} \mathrm{C}=\mathrm{CHBr}$ or $\mathrm{H}_{2} \mathrm{C}=\mathrm{CHCH}_{2} \mathrm{Br}$

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 42

Which reactant in each of the following pairs is more nucleophilic? Explain.
(a) $-\mathrm{NH}_{2}$ or $\mathrm{NH}_{3}$
(b) $\mathrm{H}_{2} \mathrm{O}$ or $\mathrm{CH}_{3} \mathrm{CO}_{2}^{-}$
(c) $\mathrm{BF}_{3}$ or $\mathrm{F}^{-}$
(d) $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{P}$ or $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}$
(e) $\mathrm{I}^{-}$ or $\mathrm{Cl}^{-}$
(f) $-\mathrm{C} \equiv \mathrm{N}$ or $-\mathrm{OCH}_{3}$

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 43

What effect would you expect the following changes to have on the rate of the $\mathrm{S}_{\mathrm{N}} 2$ reaction of 1 -iodo- 2 -methylbutane with cyanide ion?
(a) The CN $^{-}$ concentration is halved, and the 1 -iodo- 2 -methylbutane concentration is doubled.
(b) Both the CN $^{-}$ and the 1 -iodo-2-methylbutane concentrations are tripled.

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 44

What effect would you expect the following changes to have on the rate of the reaction of ethanol with 2 -iodo-2-methylbutane?
(a) The concentration of the halide is tripled.
(b) The concentration of the ethanol is halved by adding diethyl ether as an inert solvent.

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 45

How might you prepare each of the following molecules using a nucleophilic substitution reaction at some step?
(a)
(d)

Lainey Roebuck

Numerade Educator

Problem 46

Which reaction in each of the following pairs would you expect to be faster?
(a) The $\mathrm{S}_{\mathrm{N}} 2$ displacement by $\mathrm{I}^{-}$ on $\mathrm{CH}_{3} \mathrm{Cl}$ or on $\mathrm{CH}_{3} \mathrm{OTos}$
(b) The $\mathrm{S}_{\mathrm{N}}^{2}$ displacement by $\mathrm{CH}_{3} \mathrm{CO}_{2}^{-}$ on bromoethane or on bromocyclohexane
(c) The $\mathrm{S}_{\mathrm{N}}$ 2 displacement on 2 -bromopropane by $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}$ or by CN $^{-}$
(d) The $\mathrm{S}_{\mathrm{N}} 2$ displacement by $\mathrm{HC}=\mathrm{C}^{-}$ on bromomethane in benzene or in acetonitrile

Lainey Roebuck

Numerade Educator

Problem 47

Predict the product and give the stereochemistry resulting from reaction of each of the following nucleophiles with $(R)-2$ -bromooctane:
$\begin{array}{lll}\text { (a) }-\mathrm{CN} & \text { (b) } \mathrm{CH}_{3} \mathrm{CO}_{2}^{-} & \text {(c) } \mathrm{CH}_{3} \mathrm{~S}^{-}\end{array}$

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 48

$(R)-2$ -Bromooctane undergoes racemization to give $(\pm)-2$ -bromooctane when treated with NaBr in dimethyl sulfoxide. Explain.

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 49

Propose structures for compounds that fit the following descriptions:
(a) An alkyl halide that gives a mixture of three alkenes on E2 reaction
(b) An organohalide that will not undergo nucleophilic substitution
(c) An alkyl halide that gives the non-Zaitsev product on E2 reaction
(d) An alcohol that reacts rapidly with $\mathrm{HCl}$ at $0^{\circ} \mathrm{C}$

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 50

What products would you expect from the reaction of 1 -bromopropane with each of the following?
$\begin{array}{lll}\text { (a) } \mathrm{NaNH}_{2} & \text { (b) } \mathrm{KOC}\left(\mathrm{CH}_{3}\right)_{3} & \text { (c) Nal }\end{array}$
(d) NaCN
(e) $\mathrm{NaC}=\mathrm{CH}$
(f) $\mathrm{Mg}$, then $\mathrm{H}_{2} \mathrm{O}$

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 51

1 -Chloro-1,2-diphenylethane can undergo E2 elimination to give either cis- or trans-1,2-diphenylethylene (stilbene). Draw Newman projections of the reactive conformations leading to both possible products, and suggest a reason why the trans alkene is the major product.

Lainey Roebuck

Numerade Educator

Problem 52

Predict the major alkene product of the following E1 reaction:

Alexander Cheng

Alexander Cheng

Numerade Educator

Problem 53

There are eight diastereomers of 1,2,3,4,5,6 -hexachlorocyclohexane. Draw each in its more stable chair conformation. One isomer loses HCl in an E2 reaction nearly 1000 times more slowly than the others. Which isomer reacts so slowly, and why?
aneral Problems

Lainey Roebuck

Numerade Educator

Problem 54

The reactions shown below are unlikely to occur as written. Tell what is wrong with each, and predict the actual product.
(b)
(c)

Prashant Bana

Numerade Educator

Problem 55

Arrange the carbocations below, in order of increasing stability.
(a)
(b)
(c)

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 56

Order each of the following sets of compounds with respect to $\mathrm{S}_{\mathrm{N}} 1$ reactivity:
(a)
(b) $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCl}$
$\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CBr}$
$\left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH}$
(c)

Lainey Roebuck

Numerade Educator

Problem 57

Order each of the following sets of compounds with respect to $\mathrm{S}_{\mathrm{N}} 2$ reactivity:
(a)
(b)
$\begin{array}{lll}\text { (c) } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OCH}_{3} & \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OTos} & \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}\end{array}$

Lainey Roebuck

Numerade Educator

Problem 58

Predict the major product(s) of each reaction below. Identify those reactions where you would expect the product mixture to rotate planepolarized light.
(a)
(b)
(c)

Shalini Tyagi

Numerade Educator

Problem 59

Reaction of the following $S$ tosylate with cyanide ion yields a nitrile product that also has $S$ stereochemistry. Explain.
( $S$ stereochemistry)

Lainey Roebuck

Numerade Educator

Problem 60

Ethers can often be prepared by $\mathrm{S}_{\mathrm{N}}^{2}$ reaction of alkoxide ions, $\mathrm{RO}^{-}$ with alkyl halides. Suppose you wanted to prepare cyclohexyl methyl ether. Which of the two possible routes shown below would you choose? Explain.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 61

Show the stereochemistry of the epoxide (see Problem $11-31$ ) you would obtain by formation of a bromohydrin from trans-2-butene, followed by treatment with base.

Lainey Roebuck

Numerade Educator

Problem 62

In light of your answer to Problem $11-31,$ what product might you expect from treatment of 4 -bromo-1-butanol with base?
$$
\mathrm{BrCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH} \quad \stackrel{\text { Base }}{\longrightarrow} ?
$$

Lainey Roebuck

Numerade Educator

Problem 63

In addition to not undergoing substitution reactions, the alkyl bromide shown in Problem $11-32$ also fails to undergo an elimination reaction when treated with base. Explain.

Lainey Roebuck

Numerade Educator

Problem 64

The tosylate of $(2 R, 3 S)-3$ -phenyl-2-butanol undergoes E2 elimination on treatment with sodium ethoxide to yield ( $Z$ )- 2 -phenyl-2-butene. Explain, using Newman projections.

Lainey Roebuck

Numerade Educator

Problem 65

In light of your answer to Problem $11-64,$ which alkene, $E$ or $Z,$ would you expect from an $\mathrm{E} 2$ reaction on the tosylate of $(2 R, 3 \mathrm{R})-3$ -phenyl2-butanol? Which alkene would result from E2 reaction on the $(2 S, 3 R)$ and $(2 S, 3 S)$ tosylates? Explain.

Lainey Roebuck

Numerade Educator

Problem 66

How can you explain the fact that trans-1-bromo-2-methylcyclohexane yields the non-Zaitsev elimination product 3 -methylcyclohexene on treatment with base?
trans-1-Bromo-2-methylcyclohexane $\quad$ 3-Methylcyclohexene

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 67

Predict the product(s) of the following reaction, indicating stereochemistry where necessary:

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 68

Alkynes can be made by dehydrohalogenation of vinylic halides in a reaction that is essentially an E2 process. In studying the stereochemistry of this elimination, it was found that $(Z)-2$ -chloro-2-butenedioic acid reacts 50 times as fast as the corresponding $E$ isomer. What conclusion can you draw about the stereochemistry of eliminations in vinylic halides? How does this result compare with eliminations of alkyl halides?

Lainey Roebuck

Numerade Educator

Problem 69

Based on your answer to Problem $11-68,$ predict the product(s) and show the mechanism for each reaction below.
$$
\begin{array}{l}
\text { (a) } \mathrm{CH}_{3} \mathrm{CH}_{2} \\
\mathrm{C}_{\mathrm{H}}{ }^{\prime}=\mathrm{C}^{\prime}
\end{array}
$$
(b)
$$
\sum_{\mathrm{Ph}}^{\mathrm{Br}} \mathrm{C}=\mathrm{C}^{\mathrm{CH}_{3}} \frac{1 . \mathrm{Na}^{+} \mathrm{NH}_{2}}{2 . \mathrm{H}_{3} \mathrm{O}^{+}}
$$
(c)
$$
\sum_{\mathrm{Cl}}^{\mathrm{H}} \mathrm{C}=\mathrm{C}^{\mathrm{H}} \quad \frac{1 . \mathrm{Na}^{+} \mathrm{NH}_{2}}{2 . \mathrm{H}_{3} \mathrm{O}^{+}}
$$

Pronoy Sinha

Numerade Educator

Problem 70

(S)-2-Butanol slowly racemizes on standing in dilute sulfuric acid. Explain.

Shalini Tyagi

Numerade Educator

Problem 71

Reaction of $\mathrm{HBr}$ with $(\mathrm{R})-3$ -methyl- 3 -hexanol leads to racemic 3 -bromo3-methylhexane. Explain.3 -methylhexane. Explain.

George Bennett

Numerade Educator

Problem 72

Treatment of 1-bromo-2-deuterio-2-phenylethane with strong base leads to a mixture of deuterated and nondeuterated phenylethylenes in an approximately 7: 1 ratio. Explain.

Lainey Roebuck

Numerade Educator

Problem 73

Propose a structure for an alkyl halide that gives only (E)-3-methyl2-phenyl-2-pentene on E2 elimination. Make sure you indicate the stereochemistry.

Lainey Roebuck

Numerade Educator

Problem 74

Although anti periplanar geometry is preferred for E2 reactions, it isn't absolutely necessary. The deuterated bromo compound shown here reacts with strong base to yield an undeuterated alkene. Clearly, a syn elimination has occurred. Make a molecular model of the reactant, and explain the result.

Lainey Roebuck

Numerade Educator

Problem 75

In light of your answer to Problem $11-74,$ explain why one of the following isomers undergoes E2 reaction approximately 100 times as fast as the other. Which isomer is more reactive, and why?

Lainey Roebuck

Numerade Educator

Problem 76

The reaction of 1 -chlorooctane with $\mathrm{CH}_{3} \mathrm{CO}_{2}^{-}$ to give octyl acetate is greatly accelerated by adding a small quantity of iodide ion. Explain.

Travis Maslanik

Travis Maslanik

Numerade Educator

Problem 77

Compound $X$ is optically inactive and has the formula $C_{16} H_{16} B r_{2}$. On treatment with strong base, X gives hydrocarbon $\mathrm{Y}, \mathrm{C}_{16} \mathrm{H}_{14}$. Compound Y absorbs 2 equivalents of hydrogen when reduced over a palladium catalyst and reacts with ozone to give two fragments. One fragment, $\mathrm{Z}$, is an aldehyde with formula $\mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}$. The other fragment is glyoxal, (CHO) $_{2}$. Write the reactions involved, and suggest structures for $\mathbf{X}, \mathbf{Y}$ and $Z$. What is the stereochemistry of $X ?$

Lainey Roebuck

Numerade Educator

Problem 78

When a primary alcohol is treated with $p$ -toluenesulfonyl chloride at room temperature in the presence of an organic base such as pyridine, a tosylate is formed. When the same reaction is carried out at higher temperature, an alkyl chloride is often formed. Explain.

Lainey Roebuck

Numerade Educator

Problem 79

The amino acid methionine is formed by a methylation reaction of homocysteine with $N$ -methyltetrahydrofolate. The stereochemistry of the reaction has been probed by carrying out the transformation using a donor with a "chiral methyl group" that contains protium (H), deuterium (D), and tritium (T) isotopes of hydrogen. Does the methylation reaction occur with inversion or retention of configuration?

Lainey Roebuck

Numerade Educator

Problem 80

Amines are converted into alkenes by a two-step process called Hofmann elimination. S$_{\mathrm{N}} 2$ reaction of the amine with an excess of $\mathrm{CH}_{3} \mathrm{I}$
in the first step yields an intermediate that undergoes $\mathrm{E} 2$ reaction when treated with silver oxide as base. Pentylamine, for example, yields 1 -pentene. Propose a structure for the intermediate, and explain why it readily undergoes elimination.
(a) What alkyl chloride $\mathrm{B}$ reacts with amine $\mathrm{A}$ to form $\mathrm{C}$ ?
(b) Compound C is treated with $\mathrm{SOCl}_{2}$, and the product is allowed to react with magnesium metal to give a Grignard reagent $\mathbf{D}$. What is the structure of $D ?$
(c) We'll see in Section $19-7$ that Grignard reagents add to ketones, such as $\mathbf{E}$, to give tertiary alcohols, such as $\mathbf{F}$. Because of the newly formed chirality center, compound $\mathrm{F}$ exists as a pair of enantiomers. Draw both, and assign $R, S$ configuration.
(d) Two stereoisomers of flupentixol are subsequently formed from $\mathbf{F}$, but only one is shown. Draw the other isomer, and identify the type of stereoisomerism.

Lainey Roebuck

Numerade Educator