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6 Focus on Health & Medicine: Ethanol, the Most Widely Abused Drug

6 Focus on Health & Medicine: Ethanol, the Most Widely Abused Drug

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432



ORGANIC COMPOUNDS THAT CONTAIN OXYGEN, HALOGEN, OR SULFUR



CH2CH3



S

CH3CH2



S



C

N



S



CH3CH2



N

C

S



CH2CH3



Methanol (CH3OH, Section 14.4) is toxic because of these same oxidation reactions. Methanol

is oxidized by enzymes to yield formaldehyde and formic acid. Both of these oxidation products

are extremely toxic since they cannot be further metabolized by the body. As a result, the pH of

the blood decreases, and blindness and death can follow.



Antabuse



O



O

CH3



[O]



OH



C

H



alcohol

dehydrogenase



methanol



[O]

H



formaldehyde



C



aldehyde

dehydrogenase



H



OH



formic acid



Since the enzymes have a higher affinity for ethanol than methanol, methanol poisoning is

treated by giving ethanol to an individual. With both methanol and ethanol in a patient’s system,

the enzymes react more readily with ethanol, allowing the methanol to be excreted unchanged

without the formation of methanol’s toxic oxidation products.



PROBLEM 14.12



Ethylene glycol, HOCH2CH2OH, is an extremely toxic diol because its oxidation products are

also toxic. Draw the oxidation products formed during the metabolism of ethylene glycol.



14.6B HEALTH EFFECTS OF ALCOHOL CONSUMPTION

Alcohol consumption has both short-term and long-term effects. In small amounts it can cause

dizziness, giddiness, and a decrease in social inhibitions. In larger amounts it decreases coordination and reaction time and causes drowsiness. Intoxicated individuals have exaggerated emotions, slurred speech, amnesia, and a lack of coordination. Coma and death can result at even

higher concentrations.

Ethanol affects many organs. It dilates blood vessels, resulting in a flushed appearance. It increases

urine production and stimulates the secretion of stomach acid. Chronic excessive alcohol consumption damages the heart and can lead to cirrhosis of the liver, an incurable and fatal disorder

in which the liver is scarred and loses its ability to function.

The consumption of ethanol during pregnancy is not recommended. The liver of a fetus does

not contain the necessary enzyme to metabolize ethanol. As a result, any alcohol consumed

by a pregnant woman crosses the placenta and can cause a variety of abnormalities. Fetal

alcohol syndrome can result in infants of women who chronically consume alcohol during pregnancy. Infants with fetal alcohol syndrome are mentally retarded, grow poorly, and have certain

facial abnormalities. Even modest alcohol consumption during pregnancy can negatively affect

the fetus. Currently the American Medical Association recommends that a woman completely

abstain from alcohol during pregnancy.



14.7 STRUCTURE AND PROPERTIES OF ETHERS

Ethers are organic compounds that have two alkyl groups bonded to an oxygen atom. These

two alkyl groups can be the same, or they can be different.

R



O

ether



R



CH3CH2



O



CH2CH3



R groups are the same.



CH3



O



CH2CH3



R groups are different.



The oxygen atom of an ether is surrounded by two carbon atoms and two lone pairs of electrons,

giving it a bent shape like the oxygen in H2O. The C O C bond angle is similar to the tetrahedral bond angle of 109.5°.

109.5°

CH3



O



CH3



dimethyl ether



smi26573_ch14.indd 432



=

bent shape



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STRUCTURE AND PROPERTIES OF ETHERS



433



The ether oxygen can be contained in a ring. A ring that contains a heteroatom is called a

heterocycle. When the ether is part of a three-membered ring, the ether is called an epoxide.

O

H



C



C



H



H



=



H



epoxide



HEALTH NOTE

Shellfish collected during red tides

may contain high levels of neurotoxins, making it unfit for human

consumption.



a three-membered ring

with an ether O atom



Many compounds that contain ether heterocycles are naturally occurring. Disparlure, the sex

pheromone of the female gypsy moth, is an epoxide used to control the spread of the gypsy moth

caterpillar. This pest has periodically devastated the forests of the northeastern United States by

eating the leaves of many shade and fruit-bearing trees. Hemibrevetoxin B, a complex neurotoxin with four ether oxygens, is produced by algal blooms referred to as “red tides,” because of

the color of the ocean waters when these algae proliferate.

O

(CH3)2CHCH2CH2CH2CH2



C



C



H



H



(CH2)9CH3



disparlure

CH3

OH



CHO

CH2



CCH2



O



O



O

O

OH



CH3



CH2CH2CH



CHCH



CH2



hemibrevetoxin B



[Cyclic ethers are labeled in red.]



PROBLEM 14.13



What other functional groups are present in hemibrevetoxin B?



PROBLEM 14.14



Draw the structure of the three constitutional isomers of molecular formula C4H10O that

contain an ether.



14.7A PHYSICAL PROPERTIES

Because oxygen is more electronegative than carbon, the C O bonds of an ether are both polar.

Since an ether contains two polar bonds and a bent shape, it has a net dipole. In this way, ethers

resemble alcohols.

O

CH3



CH3



net dipole



two polar bonds



Ethers do not contain a hydrogen atom bonded to oxygen, so unlike alcohols, two ether molecules

cannot intermolecularly hydrogen bond to each other. This gives ethers stronger intermolecular forces than alkanes but weaker intermolecular forces than alcohols. As a result:

• Ethers have higher melting points and boiling points than hydrocarbons of comparable

size and shape.

• Ethers have lower melting points and boiling points than alcohols of comparable size

and shape.



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434



ORGANIC COMPOUNDS THAT CONTAIN OXYGEN, HALOGEN, OR SULFUR



CH3CH2CH2CH3



CH3OCH2CH3



CH3CH2CH2OH



butane

boiling point −0.5 °C



ethyl methyl ether

boiling point 11 °C



1-propanol

boiling point 97 °C



Increasing boiling point



All ethers are soluble in organic solvents. Like alcohols, low molecular weight ethers are water

soluble, because the oxygen atom of the ether can hydrogen bond to one of the hydrogens of

water. When the alkyl groups of the ether have more than a total of five carbons, the nonpolar

portion of the molecule is too large, so the ether is water insoluble.

=



CH3



=



O



O



H



H



hydrogen bond



CH3

dimethyl ether



SAMPLE PROBLEM 14.5



Rank the following compounds in order of increasing boiling point:

OCH3



CH2CH3



A



ANALYSIS

SOLUTION



CH2OH



B



C



Look at the functional groups to determine the strength of the intermolecular forces—the

stronger the forces, the higher the boiling point.

B is an alkane with nonpolar C C and C H bonds, so it has the weakest intermolecular forces

and therefore the lowest boiling point. C is an alcohol capable of intermolecular hydrogen

bonding, so it has the strongest intermolecular forces and the highest boiling point. A is an

ether, so it contains a net dipole but is incapable of intermolecular hydrogen bonding. A,

therefore, has intermolecular forces of intermediate strength and has a boiling point between

the boiling points of B and C.

CH2CH3



OCH3



B



CH2OH



A



C



Increasing intermolecular forces

Increasing boiling point



PROBLEM 14.15



Which compound in each pair has the higher boiling point?

a.



CH3(CH2)6CH3 or CH3(CH2)5OCH3



b.



PROBLEM 14.16



O



or



c.



CH3(CH2)6OH



d.



CH3(CH2)5OCH3 or CH3OCH3



or



CH3(CH2)5OCH3



Label each ether as water soluble or water insoluble.

OCH3



a.



smi26573_ch14.indd 434



CH3CH2



O



CH3



b.



O



c.



12/9/08 4:41:20 PM



FOCUS ON HEALTH & MEDICINE: ETHERS AS ANESTHETICS



14.7B



435



NAMING ETHERS



Simple ethers are usually assigned common names. To do so, name both alkyl groups bonded

to the oxygen, arrange these names alphabetically, and add the word ether. For ethers with identical alkyl groups, name the alkyl group and add the prefix di-.

CH3



O



methyl



CH2CH3



CH3CH2



ethyl



ethyl



ethyl methyl ether



O



CH2CH3

ethyl



diethyl ether



More complex ethers are named using the IUPAC system. One alkyl group is named as a hydrocarbon chain, and the other is named as part of a substituent bonded to that chain.

• Name the simpler alkyl group + O atom as an alkoxy substituent by changing the -yl

ending of the alkyl group to -oxy.

CH3O–



CH3CH2O–



methoxy



ethoxy



• Name the remaining alkyl group as an alkane, with the alkoxy group as a substituent

bonded to this chain.



SAMPLE PROBLEM 14.6



Give the IUPAC name for the following ether.

CH3CH2CH2CH2CHCH2CH2CH3

OCH2CH3



ANALYSIS AND SOLUTION



[1] Name the longer chain as an alkane and

the shorter chain as an alkoxy group.



[2] Apply other nomenclature rules to

complete the name.

4



CH3CH2CH2CH2CHCH2CH2CH3

ethoxy group



PROBLEM 14.17



CH3CH2CH2CH2CHCH2CH2CH3



OCH2CH3



8 C’s



1



OCH2CH3



octane



Answer: 4-ethoxyoctane



Name each ether.

OCH3



a.



PROBLEM 14.18



CH3



O



CH2CH2CH2CH3



c.



CH3CH2CH2



O



CH2CH2CH3



Draw the structure corresponding to each name.

a. dibutyl ether

b. ethyl propyl ether



smi26573_ch14.indd 435



b.



c. 1-methoxypentane

d. 3-ethoxyhexane



12/9/08 4:41:21 PM



436



ORGANIC COMPOUNDS THAT CONTAIN OXYGEN, HALOGEN, OR SULFUR



14.8 FOCUS ON HEALTH & MEDICINE

ETHERS AS ANESTHETICS

A general anesthetic is a drug that interferes with nerve transmission in the brain, resulting in a loss

of consciousness and the sensation of pain. The discovery that diethyl ether (CH3CH2OCH2CH3)

is a general anesthetic revolutionized surgery in the nineteenth century. Early experiments performed by a dentist, Dr. William Morton, resulted in a public demonstration of diethyl ether as an

anesthetic in Boston in 1846. Diethyl ether quickly supplanted the crude methods then used for a

patient to tolerate the excruciating pain of surgery—making an individual unconscious by excess

alcohol intake or by striking a blow to the head.



diethyl ether



Diethyl ether is an imperfect anesthetic, but considering the alternatives in the nineteenth century,

it was considered revolutionary. It is safe and easy to administer with low patient mortality, but it

is highly flammable, and it causes nausea in many patients.

For these reasons, alternatives to diethyl ether are now widely used. Many of these newer general

anesthetics, which cause little patient discomfort, are also ethers. These include isoflurane, enflurane, and methoxyflurane. Replacing some of the hydrogen atoms in the ether by halogens results

in compounds with similar anesthetic properties but decreased flammability.

F



This painting by Robert Hinckley

depicts a public demonstration of

the use of diethyl ether as an anesthetic at the Massachusetts General

Hospital in Boston, MA in the 1840s.



PROBLEM 14.19



F



C

H



O



Cl



F



C



C



H



F



F

F



isoflurane

(Trade name: Forane)



F



C



O



H



F



Cl



C



C



F



H



H

F



H



C



O



H



enflurane

(Trade name: Ethrane)



F



Cl



C



C



F



H



Cl



methoxyflurane

(Trade name: Penthrane)



Halothane (CF3CHClBr) is a general anesthetic that is not an ether. Draw a three-dimensional

structure for halothane using solid lines, wedges, and dashes (see Section 11.3).



14.9 ALKYL HALIDES

Alkyl halides have the general

molecular formula CnH2n + 1X, and

are formally derived from an alkane

by replacing a hydrogen atom with

a halogen.



Alkyl halides are organic molecules containing a halogen atom X (X = F, Cl, Br, I) bonded

to a tetrahedral carbon atom. Alkyl halides are classified as primary (1°), secondary (2°), or

tertiary (3°) depending on the number of carbons bonded to the carbon with the halogen.

Alkyl halide



Classification of alkyl halides

H



C



X



X = F, Cl, Br, I



CH3



C

H





CH3

X



CH3



C

H





CH3

X



CH3



C



X



CH3





• A primary (1°) alkyl halide has a halogen on a carbon bonded to one carbon.

• A secondary (2°) alkyl halide has a halogen on a carbon bonded to two carbons.

• A tertiary (3°) alkyl halide has a halogen on a carbon bonded to three carbons.



smi26573_ch14.indd 436



12/9/08 4:41:22 PM



ALKYL HALIDES



PROBLEM 14.20



437



Classify each alkyl halide as 1°, 2°, or 3°.

CH3



a.



CH3CH2CH2CH2CH2



b.



Br



CH3



F



c.



CH3



C



CHCH3



CH3 Cl



PROBLEM 14.21



Draw the structure of an alkyl halide that fits each description: (a) a 2° alkyl bromide of

molecular formula C4H9Br; (b) a 3° alkyl chloride of molecular formula C4H9Cl; (c) a 1° alkyl

fluoride of molecular formula C3H7F.



14.9A



PHYSICAL PROPERTIES



Alkyl halides contain a polar C X bond, but since they have all of their hydrogens bonded to

carbon, they are incapable of intermolecular hydrogen bonding. Alkyl halides with one halogen

are polar molecules, therefore, because they contain a net dipole. As a result, they have higher

melting points and boiling points than alkanes with the same number of carbons.

polar bond

C



X



H



H



H



C Cl

δ+ δ−



net dipole



X = F, Cl, Br, I



The size of the alkyl groups and the halogen also affects the physical properties of an alkyl halide.

• The boiling point and melting point of an alkyl halide increase with the size of the alkyl

group because of increased surface area.

• The boiling point and melting point of an alkyl halide increase with the size of the halogen.



Thus, CH3CH2CH2Cl has a higher boiling point than CH3CH2Cl because it has one more carbon,

giving it a larger surface area. CH3CH2CH2Br has a higher boiling point than CH3CH2CH2Cl

because Br is further down the column of the periodic table, making it larger than Cl.

CH3CH2Cl



CH3CH2CH2Cl



CH3CH2CH2Br



chloroethane

bp = 12 °C



1-chloropropane

bp = 47 °C



1-bromopropane

bp = 71 °C



Increasing boiling point

Increasing size of the alkyl group

Increasing size of the halogen



Since alkyl halides are incapable of hydrogen bonding, they are insoluble in water regardless of

size.



PROBLEM 14.22



Rank the compounds in each group in order of increasing boiling point.

a. CH3CH2CH2I, CH3CH2CH2Cl, CH3CH2CH2F

b. CH3(CH2)4CH3, CH3(CH2)5Br, CH3(CH2)5Cl



14.9B



NOMENCLATURE



In the IUPAC system, an alkyl halide is named as an alkane with a halogen substituent—that

is, as a halo alkane. To name a halogen substituent, change the -ine ending of the name of the

halogen to the suffix -o (e.g., chlorine → chloro).



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12/9/08 4:41:25 PM



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