Organic chemistry with biological applications

John E. McMurry

Chapter 6

An Overview of Organic Reactions - all with Video Answers

Educators

Chapter Questions

Problem 1

Classify each of the following reactions as an addition, elimination, substitution, or rearrangement:
(a) $\mathrm{CH}_{3} \mathrm{Br}+\mathrm{KOH} \rightarrow \mathrm{CH}_{3} \mathrm{OH}+\mathrm{KBr}$
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br} \rightarrow \mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2}+\mathrm{HBr}$
(c) $\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2}+\mathrm{H}_{2} \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{3}$

Jil Modi

Jil Modi

Rutgers, The State University of New Jersey

Problem 2

Radical chlorination of alkanes is not generally useful because mixtures of products often result when more than one kind of $\mathrm{C}-\mathrm{H}$ bond is present in the substrate. Draw and name all monochloro substitution products $\mathrm{C}_{6} \mathrm{H}_{13} \mathrm{Cl}$ you might obtain by reaction of 2 -methylpentane with $\mathrm{Cl}_{2}$.

Jil Modi

Rutgers, The State University of New Jersey

Problem 3

Using a curved arrow, propose a mechanism for formation of the cyclopentane ring of prostaglandin $\mathrm{H}_{2}$.

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 4

Which of the following species are likely to be nucleophiles and which electrophiles?
(a) $\mathrm{CH}_{3} \mathrm{Cl}$
(b) $\mathrm{CH}_{3} \mathrm{~S}^{-}$
c.
d.

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 5

An electrostatic potential map of boron trifluoride is shown. Is $\mathrm{BF}_{3}$ likely to be a nucleophile or an electrophile? Draw a Lewis structure for $\mathrm{BF}_{3}$, and explain your answer.

Julia G.

Numerade Educator

Problem 6

What product would you expect from acid-catalyzed reaction of cyclohexene with $\mathrm{H}_{2} \mathrm{O} ?$

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 7

Acid-catalyzed reaction of $\mathrm{H}_{2} \mathrm{O}$ with 2 -methylpropene yields 2 -methylpropan-2-ol. What is the structure of the carbocation formed during the reaction? Show the mechanism of the reaction.

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 8

Add curved arrows to the following polar reactions to indicate the flow of electrons in each:

Banhishikha Sinha

Banhishikha Sinha

Numerade Educator

Problem 9

Predict the products of the following polar reaction, a step in the citric acid cycle for food metabolism, by interpreting the flow of electrons indicated by the curved arrows.

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 10

Which reaction is more energetically favored, one with $\Delta G^{\circ}=-44 \mathrm{~kJ} / \mathrm{mol}$ or one with $\Delta G^{\circ}=+44 \mathrm{~kJ} / \mathrm{mol} ?$

Jil Modi

Rutgers, The State University of New Jersey

Problem 11

Which reaction is likely to be more exergonic, one with $K_{\mathrm{eq}}=1000$ or one with $K_{\mathrm{eq}}=0.001 ?$

Jil Modi

Rutgers, The State University of New Jersey

Problem 12

Which reaction is faster, one with $\Delta G^{\mp}=+45 \mathrm{~kJ} / \mathrm{mol}$ or one with $\Delta G^{\mp}=$ $+70 \mathrm{~kJ} / \mathrm{mol} ?$

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 13

Sketch an energy diagram for a two-step reaction in which both steps are exergonic and in which the second step has a higher-energy transition state than the first. Label the parts of the diagram corresponding to reactant, product, intermediate, overall $\Delta G^{\mp}$, and overall $\Delta G^{\circ}$.

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 14

The following alcohol can be prepared by addition of $\mathrm{H}_{2} \mathrm{O}$ to two different alkenes. Draw the structures of both (red $=\mathrm{O}$ ).

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 15

The following structure represents the carbocation intermediate formed in the addition reaction of HBr to two different alkenes to yield an alcohol. Draw the structures of both.

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 16

Electrostatic potential maps of (a) formaldehyde $\left(\mathrm{CH}_{2} \mathrm{O}\right)$ and (b) methanethiol $\left(\mathrm{CH}_{3} \mathrm{SH}\right)$ are shown. Is the formaldehyde carbon atom likely to be electrophilic or nucleophilic? What about the methanethiol sulfur atom? Explain.

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 17

Look at the following energy diagram:
(a) Is $\Delta G^{\circ}$ for the reaction positive or negative? Label it on the diagram.
(b) How many steps are involved in the reaction?
(c) How many transition states are there? Label them on the diagram.

Jil Modi

Rutgers, The State University of New Jersey

Problem 18

Look at the following energy diagram for an enzyme-catalyzed reaction:
(a) How many steps are involved?
(b) Which step is most exergonic?
(c) Which step is slowest?

Julia G.

Numerade Educator

Problem 19

Identify the functional groups in the following molecules, and show the polarity of each:

Crystal Wang

Numerade Educator

Problem 20

Identify the following reactions as additions, eliminations, substitutions, or rearrangements:

Crystal Wang

Numerade Educator

Problem 21

Identify the likely electrophilic and nucleophilic sites in each of the following molecules:

Crystal Wang

Numerade Educator

Problem 22

Add curved arrows to the following polar reactions to indicate the flow of electrons in each:

Madi Sousa

Numerade Educator

Problem 23

Follow the flow of electrons indicated by the curved arrows in each of the following polar reactions, and predict the products that result:

Madi Sousa

Numerade Educator

Problem 24

Alkenes undergo addition reactions when treated with HBr and HCl to give bromoalkanes and chloroalkanes, respectively. Draw the products you might expect from the following reactions:

Lottie Adams

Numerade Educator

Problem 25

When a mixture of methane and chlorine is irradiated, reaction commences immediately. When irradiation is stopped, the reaction gradually slows down but does not stop immediately. Explain.

Julia G.

Numerade Educator

Problem 26

Radical chlorination of pentane is a poor way to prepare 1 -chloropentane, but radical chlorination of neopentane, $\left(\mathrm{CH}_{3}\right)_{4} \mathrm{C}$, is a good way to prepare neopentyl chloride, $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2}$ Cl. Explain.

Julia G.

Numerade Educator

Problem 27

Despite the limitations of radical chlorination of alkanes, the reaction is still useful for synthesizing certain halogenated compounds. For which of the following compounds does radical chlorination give a single monochloro product?

Crystal Wang

Numerade Educator

Problem 28

What is the difference between a transition state and an intermediate?

Julia G.

Numerade Educator

Problem 29

Draw an energy diagram for a one-step reaction with $K_{\mathrm{eq}}<1 .$ Label the parts of the diagram corresponding to reactants, products, transition state, $\Delta G^{\circ},$ and $\Delta G^{\mp}$. Is $\Delta G^{\circ}$ positive or negative?

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 30

Draw an energy diagram for a two-step reaction with $K_{\mathrm{eq}}>1 .$ Label the overall $\Delta G^{\circ}$, transition states, and intermediate. Is $\Delta G^{\circ}$ positive or negative?

Julia G.

Numerade Educator

Problem 31

Draw an energy diagram for a two-step exergonic reaction whose second step is faster than its first step.

Julia G.

Numerade Educator

Problem 32

Draw an energy diagram for a reaction with $K_{\mathrm{eq}}=1 .$ What is the value of $\Delta G^{\circ}$ in this reaction?

Julia G.

Numerade Educator

Problem 33

As noted in Problem 6.24 , alkenes undergo addition reactions with HBr to yield bromoalkanes. The reaction of ethylene with HBr has the following thermodynamic parameters:
(a) Is the reaction exothermic or endothermic?
(b) Is the reaction favorable (spontaneous) or unfavorable (nonspontaneous) at room temperature $(298 \mathrm{~K}) ?$

Julia G.

Numerade Educator

Problem 34

When isopropylidenecyclohexane is treated with strong acid at room temperature, isomerization occurs by the mechanism shown below to yield 1 -isopropylcyclohexene:

Zubair Abdulla

Numerade Educator

Problem 35

Add curved arrows to the mechanism shown in Problem 6.34 to indicate the electron movement in each step.

Julia G.

Numerade Educator

Problem 36

2-Chloro-2-methylpropane reacts with water in three steps to yield 2-methylpropan-2-ol. The first step is slower than the second, which in turn is much slower than the third. The reaction takes place slowly at room temperature, and the equilibrium constant is near 1 .
(a) Give approximate values for $\Delta G^{\mp}$ and $\Delta G^{\circ}$ that are consistent with the above information.
(b) Draw an energy diagram for the reaction, labeling all points of interest and making sure that the relative energy levels on the diagram are consistent with the information given.

Julia G.

Numerade Educator

Problem 37

Add curved arrows to the mechanism shown in Problem 6.36 to indicate the electron movement in each step.

Julia G.

Numerade Educator

Problem 38

The reaction of hydroxide ion with chloromethane to yield methanol and chloride ion is an example of a general reaction type called a nucleophilic substitution reaction:
$$
\mathrm{HO}^{-}+\mathrm{CH}_{3} \mathrm{Cl} \rightleftarrows \mathrm{CH}_{3} \mathrm{OH}+\mathrm{Cl}^{-}
$$
The value of $\Delta H^{\circ}$ for the reaction is $-75 \mathrm{~kJ} / \mathrm{mol}$, and the value of $\Delta S^{\circ}$ is $+54 \mathrm{~J} /(\mathrm{K} \cdot \mathrm{mol}) .$ What is the value of $\Delta G^{\circ}(\mathrm{in} \mathrm{kJ} / \mathrm{mol})$ at $298 \mathrm{~K} ?$ Is the reaction exothermic or endothermic? Is it exergonic or endergonic?

Crystal Wang

Numerade Educator

Problem 39

Methoxide ion $\left(\mathrm{CH}_{3} \mathrm{O}^{-}\right)$ reacts with bromoethane in a single step according to the following equation: Identify the bonds broken and formed, and draw curved arrows to represent the flow of electrons during the reaction.

Julia G.

Numerade Educator

Problem 40

Ammonia reacts with acetyl chloride $\left(\mathrm{CH}_{3} \mathrm{COCl}\right)$ to give acetamide $\left(\mathrm{CH}_{3} \mathrm{CONH}_{2}\right)$. Identify the bonds broken and formed in each step of the reaction, and draw curved arrows to represent the flow of electrons in each step.

Crystal Wang

Numerade Educator

Problem 41

The naturally occurring molecule $\alpha$ -terpineol is biosynthesized by a route that includes the following step:
(a) Propose a likely structure for the isomeric carbocation intermediate.
(b) Show the mechanism of each step in the biosynthetic pathway, using curved arrows to indicate electron flow.

Crystal Wang

Numerade Educator

Problem 42

Predict the product(s) of each of the following biological reactions by interpreting the flow of electrons as indicated by the curved arrows:

Crystal Wang

Numerade Educator

Problem 43

Reaction of 2 -methylpropene with $\mathrm{H}_{3} \mathrm{O}^{+}$ might, in principle, lead to a mixture of two alcohol addition products. Name them, and draw their structures.

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 44

Draw the structures of the two carbocation intermediates that might form during the reaction of 2 -methylpropene with $\mathrm{H}_{3} \mathrm{O}^{+}$ (Problem 6.43 ). We'll see in the next chapter that the stability of carbocations depends on the number of alkyl substituents attached to the positively charged carbon - the more alkyl substituents there are, the more stable the cation. Which of the two carbocation intermediates you drew is more stable?

Julia G.

Numerade Educator