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Outline
14.1 Alcohols, Phenols, and Ethers
14.2 Some Common Alcohols
14.3 Naming Alcohols
14.4 Properties of Alcohols
14.5 Reactions of Alcohols
14.6 Phenols
14.7 Acidity of Alcohols and Phenols
14.8 Ethers
14.9 Thiols and Disulfides
14.10 Halogen-Containing Compounds
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Goals
1. What are the distinguishing features of alcohols, phenols,
ethers, thiols, and alkyl halides?
Be able to describe the structures and uses of compounds with
these functional groups.
2. How are alcohols, phenols, ethers, thiols, and alkyl halides
named?
Be able to give systematic names for the simple members of these
families and write their structures, given the names.
3. What are the general properties of alcohols, phenols, and
ethers?
Be able to describe such properties as polarity, hydrogen bonding,
and water solubility.
4. Why are alcohols and phenols weak acids?
Be able to explain why alcohols and phenols are acids
5. What are the main chemical reactions of alcohols and thiols?
Be able to describe and predict the products of the dehydration of
alcohols and of the oxidation of alcohols and thiols.
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14.1 Alcohols, Phenols, and Ethers
• Alcohol is a compound that has an —OH group
bonded to a saturated, alkane-like carbon atom.
• Phenol is a compound that has an —OH group
bonded directly to an aromatic, benzene-like ring.
• Ether is a compound that has an oxygen atom
bonded to two organic groups, R—O—R.
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14.1 Alcohols, Phenols, and Ethers
• The structural similarity between alcohols and
water also leads to similarities in physical
properties.
• The high boiling point of water is due to
hydrogen bonding. Hydrogen bonds also form
between alcohol (or phenol) molecules.
• Alkanes and ethers cannot form hydrogen
bonds.
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14.2 Some Common Alcohols
• METHYL ALCOHOL, CH3OH, is known as wood alcohol
because it was prepared by heating wood in the absence
of air. Today it is made by reaction of carbon monoxide
with hydrogen.
• Methanol is used industrially as a solvent, and as a
starting material for preparing formaldehyde.
• Methyl alcohol is colorless, miscible with water, and
toxic. It causes blindness in low doses (about 15 mL for
an adult) and death in larger amounts (100–250 mL).
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14.2 Some Common Alcohols
• ETHYL ALCOHOL, CH3CH2OH, is sometimes known as
grain alcohol and is the alcohol present in alcoholic
beverages.
• During fermentation, starches and sugars are converted to
simple sugars and then to ethanol by yeast enzymes.
• Fermentation can produce concentrations up to 14% ethanol,
but higher concentrations can be produced by distillation or
addition of a distilled product.
• Nonbeverage alcohol is often denatured by addition of an
unpleasant tasting and toxic substance.
• Industrially, ethyl alcohol is made by hydration of ethylene.
Distillation yields 95% ethanol, and dehydration gives 100%
or absolute ethanol.
• In some states, a blend of ethanol and gasoline is
commercially available.
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14.2 Some Common Alcohols
• ISOPROPYL ALCOHOL, (CH3)2CHOH, is often called
rubbing alcohol.
• It is used for rubdowns and in astringents, as a solvent, a
sterilant, and as a skin cleanser.
• Though less toxic than methyl alcohol, it is much more toxic
than ethanol.
• ETHYLENE GLYCOL, (HOCH2CH2OH), is a diol.
• It is a colorless liquid, miscible with water, and insoluble in
non-polar solvents.
• It is used as an engine antifreeze and coolant; it is also used
as a starting material for the manufacture of polyester.
• It is highly toxic and has a slightly sweet taste. As a result, it is
being phased out in favor of propylene glycol
(CH3CH(OH)CH2OH), which is tasteless and non-toxic.
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14.2 Some Common Alcohols
• GLYCEROL (HOCH2CH(OH)CH2OH), is a triol also called
glycerin.
• It is a colorless liquid that is miscible with water.
• It is not toxic, and has a sweet taste that makes it useful for
use in foods. It is also used as a moisturizer, in plastics
manufacture, in antifreeze and shock absorbers, and as a
solvent.
• Because of extensive hydrogen bonding, it is an extremely
viscous fluid.
• Glycerol also provides the structural backbone of animal fats
and vegetable oils.
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14.3 Naming Alcohols
• STEP 1: Name the parent compound. Find the longest
chain that has the hydroxyl substituent attached, and
name the chain by replacing the -e ending of the
corresponding alkane with -ol.
• STEP 2: Number the carbon atoms in the main chain.
Begin at the end nearer the hydroxyl group, ignoring the
location of other substituents: In a cyclic alcohol, begin
with the carbon that bears the —OH group and proceed
in a direction that gives the other substituents the lowest
possible numbers.
• STEP 3: Write the name, placing the number that
locates the hydroxyl group immediately before the
compound name. Number all other substituents, and list
them alphabetically. In a cyclic alcohol, do not use the
number 1 to specify the location of the —OH group.
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14.3 Naming Alcohols
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14.3 Naming Alcohols
• Dialcohols, or diols,
contain two hydroxy
groups in the same
molecule. The IUPAC
names of these alcohols
are formed by attaching
the ending diol to the
alkane name.
• The names will contain two
numbers indicating the
carbons bonded to the two
—OH groups, with the
numbering starting at the
end closest to one of the
—OH groups.
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14.3 Naming Alcohols
• Diols with two —OH groups on adjacent carbons are
often referred to by the common name glycols.
• This is preferably reserved for two compounds, ethylene
glycol and propylene glycol.
• Alcohols are classified as primary, secondary, or tertiary
according to the number of carbon substituents bonded
to the hydroxyl-bearing carbon.
• This classification is useful as many of the reactions of
alcohols are a function of their substitution.
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14.4 Properties of Alcohols
• Alcohols are polar because of the
electronegative oxygen atom.
• Hydrogen bonding occurs and has a
strong influence on alcohol properties.
• Straight-chain alcohols with up to 12
carbons are liquid.
• Methanol and ethanol are miscible with
water and can dissolve small amounts of
ionic compounds. Both are also miscible
with many organic solvents
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14.4 Properties of Alcohols
• All alcohols are composed of a “water-loving” or hydrophilic
part and a “water-fearing” or hydrophobic part.
• Alcohols with a larger hydrophobic part, are more like alkanes
and less like water.
• Alcohols with two or more —OH groups can form more than
one hydrogen bond. They are therefore higher boiling and
more water-soluble than similar alcohols with one —OH
group.
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14.5 Reactions of Alcohols
• DEHYDRATION: Alcohols undergo loss of water
on treatment with a strong acid.
• The reaction is driven to completion by heating.
• The —OH group is lost from one carbon, and an
—H is lost from an adjacent carbon to yield an
alkene.
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14.5 Reactions of Alcohols
• When more than one alkene can result, a
mixture of products is formed.
• The major product has the greater number of
alkyl groups directly attached to the double-bond
carbons.
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14.5 Reactions of Alcohols
Mastering Reactions: How Eliminations Occur
• When an alcohol is treated with a strong acid, the oxygen atom of
the alcohol protonates in an equilibrium process.
• This converts the —OH group into a water molecule.
• The water molecule leaves, and a carbocation remains.
• The favorability of this reaction is a function of the stability of the
carbocation. 3° alcohols undergo this process more readily than
2° alcohols, and 1° alcohols undergo the process very slowly.
• Water acting as a Lewis base, can remove an adjacent hydrogen,
forming the alkene.
• Heating selectively drives off the alkene due to its lower boiling
point.
• Zaitsev’s Rule states that the more substituted alkene will be
favored. This is the result of the equilibrium process that is
operating: the less stable form is more likely to revert to the
carbocation.
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14.5 Reactions of Alcohols
• OXIDATION occurs when primary and secondary
alcohols are converted into carbonyl-containing
compounds by an oxidizing agent.
• A carbonyl group is a carbon attached to an
oxygen by a double bond.
• Any oxidizing agent can be used.
• In organic chemistry, a more general definition of
oxidation and reduction is used.
– An organic oxidation is one that increases the number of
C—O bonds and/or decreases the number of C—H bonds.
– An organic reduction is one that decreases the number of
C—O bonds and/or increases the number of C—H bonds.
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14.5 Reactions of Alcohols
• Two hydrogen atoms are removed during the reaction;
one from the —OH group, and one from the carbon
attached to the —OH group.
• Primary alcohols are converted into aldehydes under
controlled conditions, or carboxylic acids, if an excess of
oxidant is used.
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14.5 Reactions of Alcohols
• Secondary alcohols (R2CHOH) are converted into
ketones (R2C=O) on treatment with oxidizing agents.
• Tertiary alcohols do not normally react with oxidizing
agents because they do not have a hydrogen on the
carbon atom to which the —OH group is bonded.
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14.5 Reactions of Alcohols
Ethyl Alcohol as a Drug and a Poison
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Ethyl alcohol is a central nervous system (CNS) depressant. Its direct
effects resemble the response to anesthetics.
Ethyl alcohol is absorbed in the stomach and small intestine, then
rapidly distributed to all body fluids and organs.
– In the pituitary gland, alcohol inhibits the production of a hormone that regulates
urine flow, causing increased urine production and dehydration.
– In the stomach, ethyl alcohol stimulates production of acid.
– Throughout the body, it causes blood vessels to dilate.
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Ethyl alcohol is metabolized in the liver in a two-step process: oxidation
of the alcohol to acetaldehyde, followed by oxidation of the aldehyde to
acetic acid. When continuously present, alcohol and acetaldehyde are
toxic. The liver usually suffers the worst damage because it is the major
site of alcohol metabolism.
Alcohol concentration can be measured in expired air by the color
change that occurs when the yellow-orange potassium dichromate is
reduced to blue-green chromium(III). The color change can be
interpreted by instruments to give an accurate measure of alcohol
concentration in the blood.
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14.6 Phenols
• The word phenol is the name both of a specific
compound (hydroxybenzene, C6H5OH), as well
as a family of compounds.
• Phenol itself, formerly called carbolic acid, is a
medical antiseptic that also numbs the skin.
– It was first used by Joseph Lister, who showed that
the instance of post-operative infection dramatically
decreased when phenol was used to cleanse the
operating room and the patient’s skin.
• The presence of an alkyl group lowers the
absorption through skin, rendering alkylsubstituted phenols less toxic than phenol.
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14.6 Phenols
• Some other alkyl-substituted phenols such as
the cresols (methylphenols) are common as
disinfectants.
• Phenols are usually named with the ending
phenol rather than -benzene.
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14.6 Phenols
• The properties of phenols are influenced by the
electronegative oxygen and hydrogen bonding.
• Most phenols are somewhat water-soluble and have higher
melting and boiling points than similar alkylbenzenes.
• They are less soluble in water than alcohols.
• Many biomolecules contain a hydroxyl-substituted benzene
ring.
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14.7 Acidity of Alcohols and Phenols
• Alcohols and phenols are very weakly acidic
because of the positively-polarized —OH
hydrogen.
• They dissociate slightly in solution and establish
equilibria between neutral and anionic forms.
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14.7 Acidity of Alcohols and Phenols
• Methanol and ethanol dissociate so little in water
that their aqueous solutions are neutral (pH 7).
• An alkoxide ion, or anion of an alcohol, is as
strong a base as a hydroxide ion.
• An alkoxide ion is produced by reaction of an
alkali metal with an alcohol.
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14.7 Acidity of Alcohols and Phenols
• Phenols are about 10,000 times more acidic
than water.
• A phenoxide ion is produced by reaction of a
phenol with dilute aqueous sodium hydroxide.
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14.7 Acidity of Alcohols and Phenols
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Phenols as Antioxidants
Butylated hydroxytoluene and butylated hydroxyanisole, or
their abbreviations BHT and BHA, are probably familiar.
Foods that contain unsaturated fats—those having carbon–
carbon double bonds—become rancid when oxygen from
the air reacts with their double bonds.
BHT and BHA prevent oxidation by donating a hydrogen
atom from their —OH group to the free radical as soon as it
forms.
The BHA or BHT is converted into a stable and unreactive
free radical, which causes no damage. Vitamin E, a natural
antioxidant within the body, acts similarly .
Free radicals are suspected of playing a role in both cancer
and aging of living tissue.
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14.7 Acidity of Alcohols and Phenols
Phenols as Antioxidants
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14.8 Ethers
• Ethers are named by identifying the two organic
groups and adding the word ether.
• Cyclic ethers are often referred to by their
common names.
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14.8 Ethers
• An —OR group is referred to as an alkoxy group.
• Ethers do not form hydrogen bonds to one another.
• They are higher boiling than alkanes but lower boiling
than alcohols.
• The oxygen atom in ethers can hydrogen-bond with
water, causing dimethyl ether to be water-soluble and
diethyl ether to be partially miscible with water.
• Ethers make good solvents for reactions where a polar
solvent is needed but no —OH groups can be present.
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14.8 Ethers
• Ethers are alkane-like in many properties and do
not react with acids or bases.
• Simple ethers are highly flammable.
• On standing in air, many ethers form explosive
peroxides, compounds that contain an O—O
bond. Ethers must be handled with care and
stored in the absence of oxygen.
• Diethyl ether was a mainstay of the operating
room until the 1940s. It acts quickly and is very
effective, but has a long recovery time and often
induces nausea.
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14.8 Ethers
• Ethers are found throughout the plant and
animal kingdoms. Some are present in plant oils
and are used in perfumes; others have a variety
of biological roles.
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14.9 Thiols and Disulfides
• Many oxygen-containing compounds have sulfur
analogs.
• Thiols, also called mercaptans, are sulfur
analogs of alcohols.
• The systematic name of a thiol is formed by
adding -thiol to the parent hydrocarbon name.
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14.9 Thiols and Disulfides
• The most outstanding characteristic of thiols is their
appalling odor.
• Skunk scent and the odor when garlic and onions are
being sliced are thiols.
• Natural gas is odorless, but methanethiol is added to
make leak detection easy.
• Thiols react with mild oxidizing agents to yield
disulfides. Two thiols join in this reaction, the hydrogen
from each is lost, and a bond forms between the sulfurs.
• The reverse occurs when a disulfide is treated with a
reducing agent.
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14.9 Thiols and Disulfides
Inhaled Anesthetics
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William Morton’s demonstration in 1846 of ether-induced anesthesia is one
of the most important medical breakthroughs of all time.
Hundreds of substances have subsequently been shown to act as inhaled
anesthetics.
Halothane, enflurane, isoflurane, and methoxyflurane are the most
commonly used. All are potent at low doses, nontoxic, and nonflammable.
Little is known about how inhaled anesthetics work in the body.
The potency of anesthetics correlates well with their solubility in olive oil,
leading scientists to believe that they dissolve in the membranes
surrounding nerve cells.
Depth of anesthesia is determined by the concentration of anesthetic agent
that reaches the brain.
Anesthetic potency is usually expressed as a minimum alveolar
concentration (MAC), defined as the concentration of anesthetic in inhaled
air that results in anesthesia in 50% of patients.
Nitrous oxide, is the least potent of the common anesthetics and
methoxyflurane is the most potent.
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14.9 Thiols and Disulfides
• Thiols are important because they occur in the
amino acid cysteine, which is part of many
proteins.
• The easy formation of bonds between cysteines
helps shape large protein molecules.
• The proteins in hair are unusually rich in S—S
and S—H groups.
Figure 14.2 Chemistry can curl your hair. A permanent wave
results when disulfide bridges are formed between iSH groups in hair
protein molecules.
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14.10 Halogen-Containing Compounds
• The simplest halogen-containing compounds are
alkyl halides, RX.
• Their common names consist of the name of the
alkyl group followed by the halogen name with an ide ending.
• The halogen atom is a substituent on a parent
alkane.
– The parent alkane is named in the usual way.
– The halo-substituent name is then given as a prefix, just as
if it were an alkyl group.
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14.10 Halogen-Containing Compounds
• Halogenated compounds are also used widely in
industry as solvents and degreasing agents.
• The use of halogenated herbicides and fungicides has
resulted in vastly increased crop yields in recent
decades.
• The widespread application of chlorinated insecticides,
such as DDT, is largely responsible for the progress
made toward worldwide control of malaria and typhus.
• Despite their enormous benefits, chlorinated pesticides
present problems because they persist in the
environment, remaining in the fatty tissues of organisms
and accumulating up the food chain.
• The use of many has been restricted, and others have
been banned altogether.
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Chapter Summary, Continued
1.
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What are the distinguishing features of alcohols, phenols,
ethers, thiols, and alkyl halides?
An alcohol has an —OH group (a hydroxyl group) bonded to a
saturated, alkane-like carbon atom
A phenol has an —OH group bonded directly to an aromatic ring.
An ether has an oxygen atom bonded to two organic groups.
Thiols are sulfur analogs of alcohols, R—SH
Alkyl halides contain a halogen atom bonded to an alkyl group
R—X.
The —OH group is present in many biochemically active molecules.
Phenols are notable for their use as disinfectants and antiseptics.
Ethers are used primarily as solvents.
Thiols are found in proteins.
Halogenated compounds are rare in human biochemistry, but are
widely used in industry as solvents and in agriculture as herbicides,
fungicides, and insecticides.
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Chapter Summary, Continued
2. How are alcohols, phenols, ethers, thiols,
and alkyl halides named?
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Alcohols are named using the -ol ending, and
phenols are named using the -phenol ending.
•
Ethers are named by identifying the two
organic groups attached to oxygen, followed by
the word ether.
•
Thiols use the name ending -thiol.
•
Alkyl halides are named as halo-substituted
alkanes.
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Chapter Summary, Continued
3. What are the general properties of
alcohols, phenols, and ethers?
• Both alcohols and phenols are like water
in their ability to form hydrogen bonds.
• As the size of the organic part increases,
alcohols become less soluble in water.
• Ethers do not hydrogen-bond and are
more alkane-like in their properties.
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Chapter Summary, Continued
4. Why are alcohols and phenols weak
acids?
• Like water, alcohols and phenols are
weak acids that can donate H+ from their
group to a strong base.
• Alcohols are similar to water in acidity.
• Phenols are more acidic than water and
will react with aqueous NaOH.
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Chapter Summary, Continued
5.
What are the main chemical reactions of alcohols and
thiols?
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Alcohols undergo loss of water (dehydration) to yield
alkenes when treated with a strong acid.
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They undergo oxidation to yield compounds that contain a
carbonyl group (C=O).
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Primary alcohols are oxidized to yield either aldehydes
(RCHO) or carboxylic acids (RCO2H).
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Secondary alcohols are oxidized to yield ketones (R2C=O).
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Tertiary alcohols are not oxidized.
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Thiols react with mild oxidizing agents to yield disulfides
(RSSR), a reaction of importance in protein chemistry.
•
Disulfides can be reduced back to thiols.
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