Introduction to General, Organic and Biochemistry

Frederick A. Bettelheim, William H. Brown, Mary K. Campbell

Chapter 13

Alcohols, Ethers, and Thiols - all with Video Answers

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Chapter Questions

Problem 1

Answer true or false.
(a) The functional group of an alcohol is the $-\mathrm{OH}$ (hydroxyl) group.
(b) The parent name of an alcohol is the name of the longest carbon chain that contains the $-\mathrm{OH}$ group.
(c) A primary alcohol contains one $-$ OH group, and a tertiary alcohol contains three $-\mathrm{OH}$ groups.
(d) In the IUPAC system, the presence of three $-\mathrm{OH}$ groups is shown by the ending -triol.
(e) A glycol is a compound that contains two - OH groups. The simplest glycol is ethylene glycol, $\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}$
(f) Because of the presence of an $-$ OH group, all alcohols are polar compounds.
(g) The boiling points of alcohols increase with increasing molecular weight.
(h) The solubility of alcohols in water increases with increasing molecular weight.

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Problem 2

What is the difference in structure between a primary, a secondary, and a tertiary alcohol?

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Problem 3

Which of the following are secondary alcohols?

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Problem 4

Which of the alcohols in Problem 3 are primary? Which are tertiary?

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Problem 5

Write the IUPAC name of each compound.

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Problem 6

Draw a structural formula for each alcohol.
(a) Isopropyl alcohol
(b) Propylene glycol
(c) 5 -Methyl-2-hexanol
(d) $2-$ Methyl-2-propyl-1,3-propanediol
(e) $1-$ Octanol
(f) 3,3 -Dimethylcyclohexanol

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Problem 7

Draw a structural formula for each of the following alcohols.
(a) Isobutyl alcohol
(b) $1,4-$ Butanediol
(c) 5 -Methyl-1-hexanol
(d) 1,3 -Pentanediol
(e) trans$-1,$ 4-Cyclohexanediol
(f) $1-$ Chloro- 2 -propanol

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Problem 8

Both alcohols and phenols contain an $-$ OH group.
(a) What structural feature distinguishes these two classes of compounds?
(b) Illustrate your answer by drawing the structural formulas of a phenol with six carbon atoms and an alcohol with six carbon atoms.

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Problem 9

Name the functional groups in each compound.

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Problem 10

Explain in terms of noncovalent interactions why the low-molecular-weight alcohols are soluble in water but the low-molecular-weight alkanes and alkynes are not.

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Problem 11

Explain in terms of noncovalent interactions why the low-molecular-weight alcohols are more soluble in water than the low-molecular-weight ethers.

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Problem 12

Why does the water solubility of low-molecular-weight alcohols decrease as molecular weight increases?

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Problem 13

Show hydrogen bonding between methanol and water in the following ways.
(a) Between the oxygen of methanol and a hydrogen of water
(b) Between the hydrogen of methanol's OH group and the oxygen of water

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Problem 14

Show hydrogen bonding between the oxygen of diethyl ether and a hydrogen of water.

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Problem 15

Arrange these compounds in order of increasing boiling point. Use the boiling point values of $-42^{\circ} \mathrm{C}, 78^{\circ} \mathrm{C}$ $138^{\circ} \mathrm{C},$ and $198^{\circ} \mathrm{C}$
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}$
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$
$(\mathrm{c}) \quad \mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}$
$(\mathrm{d}) \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}$

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Problem 16

Arrange these compounds in order of increasing boiling point. Use the boiling point values of $0^{\circ} \mathrm{C}, 35^{\circ} \mathrm{C}$ and $97^{\circ} \mathrm{C}$
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}$
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}$
(c) $\quad \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}$

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Problem 17

2-Propanol (isopropyl alcohol) is commonly used as rubbing alcohol to cool the skin. 2-Hexanol, also a liquid, is not suitable for this purpose. Why?

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Problem 18

Considering the hydrogen bonding intermolecular force, explain why glycerol is much thicker (more viscous than ethylene glycol, which in turn is much more viscous than ethanol.

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Problem 19

From each pair, select the compound that is more soluble in water.
$\begin{array}{lll}\text { (a) } \mathrm{CH}_{3} \mathrm{OH} & \text { or } & \mathrm{CH}_{3} \mathrm{OCH}_{3}\end{array}$
(b) $\mathrm{CH}_{3} \mathrm{CHCH}_{3}$ or
(c) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{SH} \quad$ or $\quad \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}$
$\begin{array}{lll}\text { (d) } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl} & \text { or } & \mathrm{NaCl}\end{array}$
(e) or

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Problem 20

Arrange the compounds in each set in order of decreasing solubility in water.
(a) Ethanol, butane, and diethyl ether
(b) $1-$ Hexanol, 1,2 -hexanediol, and hexane

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Problem 21

Give the structural formula of an alkene or alkenes from which each alcohol can be prepared.
(a) $2-$ Butanol
(b) $1-$ Methylcyclohexanol
(c) $3-$ Hexanol
(d) 2 -Methyl-2-pentanol
(e) Cyclopentanol

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Problem 22

Answer true or false.
(a) The two most important reactions of alcohols are their acid-catalyzed dehydration to give alkenes and their oxidation to aldehydes, ketones, and carboxylic acids.
(b) The acidity of alcohols is comparable to that of water
(c) Water-insoluble alcohols and water-insoluble phenols react with strong bases to give water-soluble salts.
(d) Acid-catalyzed dehydration of cyclohexanol gives cyclohexane.
(e) When the acid-catalyzed dehydration of an alcohol can yield isomeric alkenes, the alkene with the greater number of hydrogens on the carbons of the double bond generally predominates.
(f) The acid-catalyzed dehydration of 2-butanol gives predominantly 1-butene.
(g) The oxidation of a primary alcohol gives either an aldehyde or a carboxylic acid depending on experimental conditions.
(h) The oxidation of a secondary alcohol gives a carboxylic acid.
(i) Acetic acid, $\mathrm{CH}_{3} \mathrm{COOH}$, can be prepared from ethylene, $\mathrm{CH}_{2}=\mathrm{CH}_{2}$, by treatment of ethylene with $\mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4},$ followed by treatment with $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} / \mathrm{H}_{2} \mathrm{SO}_{4}$
(j) Treatment of propene, $\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2},$ with $\mathrm{H}_{2} \mathrm{O} /$
$\mathrm{H}_{2} \mathrm{SO}_{4}$ followed by treatment with $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} / \mathrm{H}_{2} \mathrm{SO}_{4}$
gives propanoic acid, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}$

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Problem 23

Show how to distinguish between cyclohexanol and cyclohexene by a simple chemical test. Tell what you would do, what you would expect to see, and how you would interpret your observation.

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Problem 24

Compare the acidity of alcohols and phenols, which are both classes of organic compounds that contain an $-$ OH group.

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Problem 25

Both 2,6 -diisopropylcyclohexanol and the intravenous anesthetic Propofol are insoluble in water. Show how these two compounds can be distinguished by their reaction with aqueous sodium hydroxide.

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Problem 26

Write equations for the reaction of 1 -butanol, a primary alcohol, with these reagents.
(a) $\mathrm{H}_{2} \mathrm{SO}_{4},$ heat
(b) $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}, \mathrm{H}_{2} \mathrm{SO}_{4}$

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Problem 27

Write equations for the reaction of 2 -butanol with these reagents.
(a) $\mathrm{H}_{2} \mathrm{SO}_{4},$ heat
(b) $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}, \mathrm{H}_{2} \mathrm{SO}_{4}$

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Problem 28

Write equations for the reaction of each of the following compounds with $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} / \mathrm{H}_{2} \mathrm{SO}_{4}$
(a) $1-$ Octanol
(b) 1,4 -Butanediol

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Problem 29

Show how to convert cyclohexanol to these compounds.
(a) Cyclohexene
(b) Cyclohexane
(c) Cyclohexanone
(d) Bromocyclohexane

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Problem 30

Show reagents and experimental conditions to synthesize each compound from 1-propanol which is in the blue box.

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Problem 31

Show how to convert this alcohol to compounds
(a) and (b).

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Problem 32

Name two important alcohols derived from ethylene and give two important uses of each.

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Problem 33

Name two important alcohols derived from propene and give two important uses of each.

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Problem 34

Answer true or false.
(a) Ethanol and dimethyl ether are constitutional isomers.
(b) The solubility of low-molecular-weight ethers in water is comparable to that of low-molecularweight alcohols in water
(c) Ethers undergo many of the same reactions that alcohols do.

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Problem 35

Write the common name for each ether.

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Problem 36

Write the common name for each of the following ethers.

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Problem 37

Answer true or false.
(a) The functional group of a thiol is the $-\mathrm{SH}$ (sulfhydryl) group.
(b) The parent name of a thiol is the name of the longest carbon chain that contains the $-$ SH group.
(c) The S-H bond is nonpolar covalent.
(d) The acidity of ethanethiol is comparable to that of phenol.
(e) Both phenols and thiols are classified as weak acids.
(f) The most common biological reaction of thiols is their oxidation to disulfides.
(g) The functional group of a disulfide is the $-\mathrm{S}-\mathrm{S}-$ group.
(h) Conversion of a thiol to a disulfide is a reduction reaction.

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Problem 38

Write the IUPAC name of each thiol.

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Problem 39

Write the common name for each thiol in
Problem 38.

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Problem 40

Following are structural formulas for 1 -butanol and 1-butanethiol. One of these compounds has a boiling point of $98^{\circ} \mathrm{C}$ and the other has a boiling point of $117^{\circ} \mathrm{C} .$ Which compound has which boiling point?
\[
\begin{array}{cc}
\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH} & \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{SH} \\
1-\text { Butanol } & 1 \text { -Butanethiol }
\end{array}
\]

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Problem 41

Explain why methanethiol, $\mathrm{CH}_{3} \mathrm{SH}$, has a lower boiling point $\left(6^{\circ} \mathrm{C}\right)$ than methanol, $\mathrm{CH}_{3} \mathrm{OH}\left(65^{\circ} \mathrm{C}\right)$, even though methanethiol has a higher molecular weight.

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Problem 42

Answer true or false.
(a) Today, the major carbon sources for the synthesis of methanol are coal and methane (natural gas), both nonrenewable resources.
(b) Today the major carbon sources for the synthesis of ethanol are petroleum and natural gas, both nonrenewable resources.
(c) Intermolecular acid-catalyzed dehydration of ethanol gives diethyl ether.
(d) Conversion of ethylene to ethylene glycol involves oxidation to ethylene oxide, followed by acidcatalyzed hydration (addition of water) to ethylene oxide.
(e) Ethylene glycol is soluble in water in all proportions.
(f) A major use of ethylene glycol is as automobile antifreeze.

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Problem 43

(Chemical Connections 13 A) As stated in the Chemical Connection, "Hydrogen bonds have directionality in that the donor and acceptor groups must be oriented appropriately with respect to each other for hydrogen bonding to occur." Describe the directionality of hydrogen bonding observed in figure ( $b$ ) of the Chemical Connection.

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Problem 44

(Chemical Connections $13 \mathrm{B}$ ) What is the color of dichromate ion, $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ ? What is the color of chromi$\mathrm{um}(\mathrm{III})$ ion, $\mathrm{Cr}^{3+} ?$ Explain how the conversion of one to the other is used in breath-alcohol screening.

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Problem 45

(Chemical Connections 13 B) The legal definition of being under the influence of alcohol is based on blood alcohol content. What is the relationship between breath alcohol content and blood alcohol content?

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Problem 46

(Chemical Connections $13 \mathrm{C}$ ) What does it mean
to say that ethylene oxide is a highly strained molecule?

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Problem 47

(Chemical Connections 13 D) What are the advantages and disadvantages of using diethyl ether as an anesthetic?

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Problem 48

(Chemical Connections 13 D) Show that enflurane and isoflurane are constitutional isomers.

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Problem 49

(Chemical Connections 13 D) Would you expect enflurane and isoflurane to be soluble in water? Would you expect them to be soluble in organic solvents such as hexane?

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Problem 50

Write a balanced equation for the complete combustion of ethanol, the alcohol blended with gasoline to produce E85.

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Problem 51

Knowing what you do about electronegativity, the polarity of covalent bonds, and hydrogen bonding, would you expect an $\mathrm{N}-\mathrm{H}-\mathrm{N}$ hydrogen bond to be stronger than, the same strength as, or weaker than an O-H- -O hydrogen bond?

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Problem 52

Draw structural formulas and write IUPAC names for the eight isomeric alcohols with the molecular formula $\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}$.

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Problem 53

Draw structural formulas and write common names for the six isomeric ethers with the molecular formula $\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}$.

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Problem 54

Explain why the boiling point of ethylene glycol $\left(198^{\circ} \mathrm{C}\right)$ is so much higher than that of 1 -propanol $\left(97^{\circ} \mathrm{C}\right)$, even though their molecular weights are about the same.

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Problem 55

Following is a structural formula for erythromycin A, a macrolactone (macrolide) antibiotic.
(a) How many hydroxyl groups are present? Classify each as primary $\left(1^{\circ}\right),$ secondary $\left(2^{\circ}\right),$ or tertiary $\left(3^{\circ}\right)$
(b) How many amine groups are present? Classify each as primary $\left(1^{\circ}\right),$ secondary $\left(2^{\circ}\right),$ or tertiary $\left(3^{\circ}\right)$
(c) Locate the ester group within the large 15 -member ring.
(d) Four of the hydroxyl groups within Erythromycin A are involved in intramolecular (internal) hydrogen bonds. One of these is pointed out on the structural formula. Note that this hydrogen bond creates a five-membered ring. Locate the other three intramolecular hydrogen bonds and specify the size of the ring created by each.

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Problem 56

1,4 -Butanediol, hexane, and 1 -pentanol have similar molecular weights. Their boiling points, arranged from lowest to highest, are $69^{\circ} \mathrm{C}, 138^{\circ} \mathrm{C},$ and $230^{\circ} \mathrm{C}$
Which compound has which boiling point?

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Problem 57

Of the three compounds given in Problem 56 , one is insoluble in water, another has a solubility of $2.3 \mathrm{g} / 100 \mathrm{g}$ water, and one is infinitely soluble in water. Which compound has which solubility?

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Problem 58

Each of the following compounds is a common organic solvent. From each pair of compounds, select the solvent with the greater solubility in water.
(a) $\mathrm{CH}_{2} \mathrm{Cl}_{2}$ or $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}$ or $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$

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Problem 59

Show how to prepare each compound from 2-methyl-1-propanol.
(a) $2-$ Methylpropene
(b) $2-$ Methyl-2-propanol
(c) 2 -Methylpropanoic acid, $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCOOH}$

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Problem 60

Show how to prepare each compound from 2-methylcyclohexanol.

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Problem 61

The mechanism of the acid-catalyzed dehydration of an alcohol to an alkene is the reverse of the acid-catalyzed hydration of an alkene. The dehydration mechanism occurs by the following three steps.
Step 1: Add a proton.
Step 2: Break a bond to form stable molecules or ions.
Step 3: Take away a proton.
These three steps are illustrated here by the dehydration of 2 -butanol to give 2 -butene. Use curved arrows to show the flow of electrons in each step; that is, show how each bond-making or bond-breaking step occurs.

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Problem 62

Use the reactions we learned in Chapter 12 and this chapter to show how to bring about the following chemical transformations. Some transformations will require only one step. Others will require two or more steps.

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Problem 63

Lipoic acid is a growth factor for many bacteria and protozoa and an essential component of several enzymes involved in human metabolism.
(a) Name the two functional groups in lipoic acid.
(b) At one stage in its function in human metabolism, the disulfide bond of lipoic acid is reduced to two thiol groups. Draw a structural formula for this reduced form of lipoic acid.

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Problem 64

Following is a structural formula for the amino acid cysteine:
(a) Name the three functional groups in cysteine.
(b) In the human body, cysteine is oxidized to cystine, a disulfide. Draw a structural formula for cystine.

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Problem 65

As we will see in Chapter $15,$ the carbonyl group of aldehydes and ketones reacts with water to form a compound called a hydrate. The hydration of a carbonyl group is catalyzed by acid. Formaldehyde, for example, reacts as shown below. When dissolved in water, formaldehyde exists almost entirely as its hydrate. This aqueous solution is given the name formalin.
The mechanism for this acid-catalyzed hydration is similar to the mechanism for the acid-catalyzed hydration of an alkene to give an alcohol and occurs by the following three steps. Step 1: Add a proton. Step 2: Make a new covalent bond between an electrophile (an electron-seeking species) and a nucleophile (an electron-donating species). Step 3: Take a proton away. Write an equation for each step and show by the use of curved arrows how each of these steps occurs. Show all bond-forming steps and bond-breaking steps.

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Problem 66

Draw the structural formula for the hydrate formed by the reaction of acetone with water.

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Problem 67

With the exception of the acid-catalyzed conversion of ethylene to ethanol, primary alcohols cannot be prepared by the acid-catalyzed hydration of alkenes. The acid-catalyzed conversion of almost all other alkenes gives either secondary or tertiary alcohols. Explain why these two generalizations are valid.

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Problem 68

Consider alkenes $A, B,$ and $C .$ each of which has the same molecular formula, $\mathrm{C}_{6} \mathrm{H}_{12}$. Alkenes $\mathrm{B}$ and $\mathrm{C}$ can each be separated into cis and trans isomers. Upon catalytic reduction using $\mathrm{H}_{2}$ in the presence of a transition metal catalyst (Ni, Pd, or Pt), alkenes A, B, and C all give hexane as the only product. Acid-catalyzed hydration of alkene $C$ gives one alcohol with the molecular formula $\mathrm{C}_{6} \mathrm{H}_{14} \mathrm{O}$. Acid-catalyzed hydration of alkene B gives an equal mixture of two alcohols, each with the molecular formula $\mathrm{C}_{6} \mathrm{H}_{14} \mathrm{O}$. Acid-catalyzed hydration of alkene $C$ gives only a single alcohol with the molecular formula $\mathrm{C}_{6} \mathrm{H}_{14}$ O. Propose structural formulas for alkenes $A, B,$ and $C$ and the alcohols formed by acid-catalyzed hydration of each, consistent with these experimental results.

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Problem 69

On acid-catalyzed hydration of alkenes A and C in the previous problem, each gives only one alcohol with the molecular formula $\mathrm{C}_{6} \mathrm{H}_{14} \mathrm{O}$. Draw the structural formulas for five other alkenes with the molecular formula $\mathrm{C}_{6} \mathrm{H}_{12}$, each of which will also give only one alcohol upon acid-catalyzed hydration.

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