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8 Focus on Health & Medicine: Ethers as Anesthetics
Classify each alkyl halide as 1°, 2°, or 3°.
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.
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.
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.
bp = 12 °C
bp = 47 °C
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
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
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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ORGANIC COMPOUNDS THAT CONTAIN OXYGEN, HALOGEN, OR SULFUR
Name an Alkyl Halide Using the IUPAC System
Give the IUPAC name of the following alkyl halide.
Find the parent carbon chain containing the halogen.
7 C’s in the longest chain
• Name the parent chain as an alkane, with the halogen as a
substituent bonded to the longest chain.
Apply all other rules of nomenclature.
a. Number the chain.
b. Name and number the substituents.
methyl at C5
chloro at C2
• Begin at the end nearest the first
substituent, either alkyl or halogen.
c. Alphabetize: c for chloro, then m for methyl.
Common names for alkyl halides are used only for simple alkyl halides. To assign a common
name, name the carbon atoms as an alkyl group. Then name the halogen by changing the -ine
ending of the halogen name to the suffix -ide; for example, bromine → bromide.
Common name: ethyl chloride
Give the IUPAC name for each compound.
Give the structure corresponding to each name.
d. propyl chloride
14.9C INTERESTING ALKYL HALIDES
Many simple alkyl halides make excellent solvents because they are not flammable and they
dissolve a wide variety of organic compounds. Two compounds in this category include CHCl3
(chloroform or trichloromethane) and CCl4 (carbon tetrachloride or tetrachloromethane). Large
quantities of these solvents are produced industrially each year, but like many chlorinated organic
compounds, both chloroform and carbon tetrachloride are toxic if inhaled or ingested. Two other
simple alkyl halides are given in Figure 14.5.
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FIGURE 14.5 Two Simple Alkyl Halides
• Chloromethane (CH3Cl) is produced by giant kelp and algae and is also
found in emissions from volcanoes such as Hawaii’s Kilauea. Almost all of
the atmospheric chloromethane results from these natural sources.
• Dichloromethane (or methylene chloride, CH2Cl2) is an important
solvent, once used to decaffeinate coffee. Coffee is now decaffeinated
using liquid CO2 due to concerns over the possible ill effects of trace
amounts of residual CH2Cl2 in the coffee. Subsequent studies on rats
have shown, however, that no cancers occurred when animals ingested
the equivalent of over 100,000 cups of decaffeinated coffee per day.
The 1995 Nobel Prize in Chemistry
was awarded to Professors
Mario Molina, Paul Crutzen, and
F. Sherwood Rowland for their work
in elucidating the interaction of ozone
with CFCs. What began as a very
fundamental research project turned
out to have important implications in
the practical world.
FOCUS ON THE ENVIRONMENT
ALKYL HALIDES AND THE OZONE LAYER
While the beneficial effects of many organic halides are undisputed, certain synthetic chlorinated organics, such as the chlorofluorocarbons, have caused lasting harm to the environment.
Chlorofluorocarbons (CFCs) are simple halogen-containing compounds having the general
molecular structure CFxCl4 – x. CFCs are manufactured under the trade name Freons. Two
examples are CFCl3 (Freon 11) and CF2Cl2 (Freon 12).
CFCs are inert and nontoxic, and they have been used as refrigerants, solvents, and aerosol propellants. Because CFCs have low boiling points and are water insoluble, they readily escape into
the upper atmosphere. There, CFCs are decomposed by sunlight. This process forms highly reactive intermediates that have been shown to destroy the ozone layer (Figure 14.6).
FIGURE 14.6 CFCs and Ozone Destruction
• CFCs are decomposed by sunlight.
• The reactive intermediates convert
ozone (O3) to oxygen (O2).
CFCs used at ground level
escape to the upper atmosphere.
Propane and butane are now used
as propellants in spray cans in place
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ORGANIC COMPOUNDS THAT CONTAIN OXYGEN, HALOGEN, OR SULFUR
The ozone (O3) in the upper atmosphere is vital to life: it acts as a shield, protecting the earth’s
surface from destructive ultraviolet radiation. A decrease in ozone concentration in this protective layer will have some immediate consequences, including an increase in the incidence of skin
cancer and eye cataracts. Other long-term effects include a reduced immune response, interference with photosynthesis in plants, and harmful effects on the growth of plankton, the mainstay
of the ocean food chain.
These findings led to a ban on the use of CFCs in aerosol propellants in the United States in 1978
and to the phasing out of their use in refrigeration systems. While it is now easy to second-guess
the extensive use of CFCs, it is also easy to see why they were used so widely. CFCs made
refrigeration available to the general public. Would you call your refrigerator a comfort or a
O3 destruction is most severe in
the region of the South Pole, where
a large ozone hole (shown in purple)
is visible with satellite imaging.
There are two newer alternatives to CFCs. Hydrochlorofluorocarbons (HCFCs) such as
CF3CHCl2 contain the elements of H, Cl, and F bonded to carbon, and hydrofluorocarbons
(HFCs) such as FCH2CF3 contain the elements of H and F bonded to carbon. These compounds
have many properties in common with CFCs, but they are decomposed more readily before they
reach the upper atmosphere, so they are less destructive to the O3 layer.
Classify each compound as a CFC, HCFC, or HFC: (a) CF3Cl; (b) CHFCl2; (c) CH2F2.
14.10 ORGANIC COMPOUNDS THAT CONTAIN SULFUR
Thiols are organic compounds that contain a sulfhydryl group (SH group) bonded to a
tetrahedral carbon. Since sulfur is directly below oxygen in the periodic table, thiols can be
considered sulfur analogues of alcohols. Because the sulfur atom is surrounded by two atoms and
two lone pairs, thiols have a bent shape around sulfur.
bent shape around S
Thiols differ from alcohols in one important way. They contain no O H bonds, so they are incapable of intermolecular hydrogen bonding. This gives thiols lower boiling points and melting
points compared to alcohols having the same size and shape.
Hydrogen bonding can occur.
stronger intermolecular forces
higher boiling point
bp 78 °C
bp 35 °C
Hydrogen bonding is impossible.
weaker intermolecular forces
lower boiling point
To name a thiol in the IUPAC system:
• Name the parent hydrocarbon as an alkane and add the sufﬁx -thiol.
• Number the carbon chain to give the SH group the lower number.
Begin numbering at this C.
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