Chapter 23 Functional Groups

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Chapter 23Functional Groups
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Functional Groups
Most organic chemistry involves substituents,
which are groups attached to hydrocarbon chains.
The substituents of organic molecules often
contain oxygen, nitrogen, sulfur and phosphorus.
They are called functional groups because they
are the chemically functional parts of the
molecules. Organic compounds can be classified
according to their functional groups. They
symbol R represents any carbon chains or rings
attached to the functional group.
? And ? bonds of alkenes and alkynes are
chemically reactive and are also considered
functional groups.
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Halogen Substituents
Halocarbons in which a halogen is attached to a
carbon of an aliphatic chain are called alkyl
halides. The number of carbon atoms attached to
the alkyl group determines whether the carbon is
primary, secondary, or tertiary. Halocarbons in
which a halogen is attached to a carbon of an
arene (aromatic hydrocarbon) ring are called aryl
halides. The attractions between halocarbon
molecules are primarily the result of weak van
der Waals interactions called dispersion forces.
The attractions increase with the degree of
halogen substitution.
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Halogen Substituents
The more highly halogenated organic compounds
have higher boiling points. Very few halocarbons
are found in nature, but they can be readily
prepared and used for many purposes.
Hydrofluorocarbons are used as refrigerants in
automobile air conditioning systems. Halothan
(2-bromo-2-chloro-1,1,1,-trifluoroethane) is used
and an anesthetic.
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Effect of Structure on Boiling Point
CH3CH2CH3
CH3CH2OH
CH3CH2F
Molecularweight Boilingpoint, C

• 44 48 46
• -42 -32 78

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Effect of Structure on Boiling Point
CH3CH2CH3
Molecularweight Boilingpoint, C
Intermolecular forcesare weak. Only
intermolecular forces are induced dipole-induced
dipole attractions.

• 44
• -42

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Effect of Structure on Boiling Point
CH3CH2F
A polar moleculetherefore dipole-dipoleand
dipole-induceddipole forces contributeto
intermolecular attractions.
Molecularweight Boilingpoint,
C Dipolemoment, D

• 48
• -32
• 1.9

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Effect of Structure on Boiling Point
CH3CH2OH
Molecularweight Boilingpoint,
C Dipolemoment, D
Highest boiling pointstrongest
intermolecularattractive forces. Hydrogen
bonding isstronger than other dipole-dipole
attractions.

• 46
• 78
• 1.7

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Halogen Substituents
Chloromethane (methyl chloride)
Chlorobenzene (phenyl chloride)
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Nomenclature of Alkyl Halides

• Name the alkyl group and the halogen asseparate
  words (alkyl halide)

CH3F
CH3CH2CH2CH2CH2Cl
Methyl fluoride
Pentyl chloride
1-Ethylbutyl bromide
Cyclohexyl iodide
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Nomenclature of Alkyl Halides

• Name as halo-substituted alkanes.
• Number the longest chain containing thehalogen
  in the direction that gives the lowestnumber to
  the substituted carbon.

CH3CH2CH2CH2CH2F
1-Fluoropentane
2-Bromopentane
3-Iodopentane
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Nomenclature of Alkyl Halides

• Halogen and alkyl groupsare of equal rank when
  it comes to numberingthe chain.
• Number the chain in thedirection that gives the
  lowest number to thegroup (halogen or
  alkyl)that appears first.

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Nomenclature of Alkyl Halides
5-Chloro-2-methylheptane
2-Chloro-5-methylheptane
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Nomenclature of Alkyl Halides
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1,2 or 1,3 or 1,4-dichlorobenzene
chlorobenzene
chloromethylbenzene
benzyl chloride
Aryl Halides
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Classification

• Alcohols and alkyl halides are classified
  as primary secondary tertiaryaccording to
  their "degree of substitution."
• Degree of substitution is determined by
  countingthe number of carbon atoms directly
  attached tothe carbon that bears the halogen or
  hydroxyl group.

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Classification
H
CH3CH2CH2CH2CH2F
OH
primary alkyl halide
secondary alcohol
secondary alkyl halide
tertiary alcohol
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Structural formula Name
CH3- Methyl-
CH3CH2- Ethyl-
CH3CH2CH2- propyl- or n-propyl
(CH3)2CH- Isopropyl-
CH3CH2CH2CH2- butyl- or n-butyl
CH3CHCH2CH3 sec-butyl- or s-butyl
(CH3)2CHCH2- isobutyl
(CH3)3C- tert-butyl or t-butyl
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Substitution Reactions
Organic reactions often proceed more slowly than
inorganic reactions. Organic reactions commonly
involve the breaking of relatively strong
covalent bonds. Catalysts are often needed. Many
organic reactions are complex, often producing a
mixture of products. The desired product must
then be separated by distillation,
crystallization, or other means. A common type
of organic reaction is a substitution reaction,
in which an atom or a group of atoms replaces
another atom or group of atoms.
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Substitution Reactions
A halogen can replace a hydrogen atom on an
alkane to produce a halocarbon. CH4 Cl2
? CH3Cl HCl Sunlight or another
source of ultraviolet radiation usually serves as
a catalyst. Even under controlled conditions,
this simple halogenation reaction produces a
mixture of mono-, di-, tri-, and
tetrachloromethanes.
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Substitution Reactions
Iron compounds are often used as catalysts for
aromatic substitution reactions. Halogens on
carbon chains are readily displace by hydroxide
ions to produce an alcohol and a salt. CH3I
KOH ? CH3OH KI
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Substitution Reactions
Iron compounds are often used as catalysts for
aromatic substitution reactions. Halogens on
carbon chains are readily displace by hydroxide
ions to produce an alcohol and a salt. CH3I
KOH ? CH3OH KI Fluoro groups are not
easily displaced. Thus, fluorocarbons are seldom,
if ever, used to make alcohols.
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Questions
How are organic compounds classified? According
to their functional groups What is a
halocarbon? Class of organic compounds containing
covalently bonded fluorine, chlorine, bromine, or
iodine. How can a halocarbon be prepared? By
reacting an alkane with a halogen, catalyzed by
UV light.
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Questions
Identify the functional group in each
structure Isopropyl chloride hydroxyl CH3 CH2
NH2 amino CH3 CH2 CH2 Br Halogen CH3 CH2
O CH2 CH3 ether
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Questions
Give the structural formula for the
compound Isopropyl chloride CH3 CH3
C Cl H
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Questions
Give the structural formula for the
compound 1-iodo-2,2-dimethylpentane
CH3
I CH2 C CH2 CH2
CH3
CH3
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Questions
Give the structural formula for the
compound P-bromotoluene Write the names of all
possible dichloropropanes that could form from
the chlorination of propane. 1,1,-dichloropropan
e 1,2-dichloropropane 2,2-dichloropropane 1,3-dich
loropropane
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Questions
Write the structural formulas for ethene, ethyl
chloride, and ethanol. Identify their
functional groups. Choose two of the compounds
to illustrate a substitution reaction. Explain
the terms primary, secondary and tertiary.

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End of Section 23.1
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Alcohols
The OH functional group in alcohols is called a
hydroxyl group. Aliphatic alcohols can be
classified into structural categories according
to the number of R groups attached to the carbon
with the hydroxyl group.
Primary
Secondary
Tertiary
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Naming Alcohols - IUPAC
When using the IUPAC system to name
continuous-chain substituted alcohols, drop the
e ending of the parent alkane name and add the
ending ol. The parent alkane is the longest
continuous chain of C that includes the C
attached to the hydroxyl group. In numbering the
longest continuous chain, the position of the
hydroxyl group is given the lowest possible
number. Alcohols containing two, three, and four
OH substituents are name diols, triols, and
tetrols, respectively..
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Common Names - Alcohol
Common names of aliphatic alcohols are written in
the same way as those of the halocarbons.
The alkyl group ethyl, for example, is named and
followed by the word alcohol, as in ethyl
alcohol. Compounds with more than one OH
substituent are called glycols.
Methanol Methyl alcohol
Ethanol Ethyl alcohol
2-propanol Propyl alcohol
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Naming Alcohols
2-butanol sec-butyl alcohol
2-methyl-2-propanol tert-butyl alcohol
2-propanol isopropyl alcohol
2-methyl-1-propanol isobutyl alcohol
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Naming Alcohols
1,2,3-propanetriol glycerol (glycerin)
1,2-ethanediol ethylene glycol
2-propanol isopropyl alcohol
2-methyl-1-propanol isobutyl alcohol
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Properties of Alcohols
Alcohols are capable of intermolecular hydrogen
bonding. Therefore, they boil at higher
temperatures than alkanes and halocarbons
containing comparable numbers of atoms. Because
alcohols are derivatives of water, (the hydroxyl
group is part of a water molecule) they are
somewhat soluble. Alcohols of up to four carbons
are soluble in water in all proportions. The
solubility of alcohols with four or more carbons
in the chain is usually much lower.
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Properties of Alcohols
Alcohols consist of two parts the carbon chain
and the hydroxyl group. The carbon chain is
nonpolar and is not attracted to water. The
hydroxyl group is polar and strongly interacts
with water through hydrogen bonding. For
alcohols of up to four carbons, the polarity of
the hydroxyl group is more significant than the
nonpolarity of the carbon chain. These alcohols
are soluble in water. As the number of carbon
atoms increases above four, the nonpolarity of
the chain becomes more significant, and the
solubility decreases.
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Properties of Alcohols
Many aliphatic alcohols are used in laboratories,
clinics and industry as rubbing alcohol,
antiseptic and as a base for perfumes, creams,
lotions and other cosmetics. Ethylene glycol
(1,2-ethanediol) is the principal ingredient of
certain antifreezes. Ethyl alcohol is called
grain alcohol and is an important industrial
chemical. Most ethanol is still produced by yeast
fermentation of sugar. Fermentation is the
production of ethanol from sugars by the action
of yeast or bacteria.
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Properties of Alcohols
Ethanol is the intoxication substance in
alcoholic beverages. It is a depressant and can
be fatal if taken in large doses at once. The
ethanol used in industrial application is
denatured. Denatured alcohol is ethanol with an
added substance to make it toxic. The added
substance is often methyl alcohol, which is
sometimes called wood alcohol because it used to
be prepared by the distillation of wood. Wood
alcohol is extremely toxic. As little as 10 mL
has been reported to cause permanent blindness
and as little as 30 mL to can cause death.
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Addition Reactions
The carbon-carbon single bonds in alkanes are not
easy to break. In alkenes one of the bonds in the
double bond is somewhat weaker and is easier to
break than a carbon-carbon single bond. It is
sometimes possible for a compound of general
structure X-Y to add to a double bond. In an
addition reaction, a substance is added at the
double or triple bond of an alkene or alkyne.
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Addition Reactions
Addition reactions of alkenes are an important
method of introducing new functional groups into
organic molecules. In alkenes one of the bonds
in the double bond is somewhat weaker and is
easier to break than a carbon-carbon single bond.
It is sometimes possible for a compound of
general structure X-Y to add to a double bond.
In an addition reaction, a substance is added at
the double or triple bond of an alkene or alkyne.
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Addition Reactions
The addition of water to an alkene is a hydration
reaction. Hydration reactions usually occur when
the alkene and water are heated to about 100ºC in
the presence of a trace of strong acid. (The acid
usually HCl or H2SO4, serves as a catalyst for
the reaction.) When the reagent is a halogen, a
disubstituted halocarbon is produced.
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Addition Reactions
The addition of bromine to carbon-carbon multiple
bonds is often used as a chemical test for
unsaturation in an organic molecule. Bromine has
a brownish-orange color, but most organic
compounds of bromine are colorless. The loss of
the orange color is a positive test for
unsaturation. If the orange remains, the sample
is completely saturated.
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Hydrogenation Reactions
Hydrogen halides can also be added to a double
bond. The product is called a monosubstituted
halocarbon because it only has one
substituent. The addition of hydrogen to a
carbon-carbon double bond to produce an alkane is
called a hydrogenation reaction. Hydrogenation
reactions usually require a catalyst. Platinum
or paladium are often used. The manufacture of
margarine from unsaturated vegetable oils is a
common application of a hydrogenation reaction.
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Hydrogenation Reactions
The hydrogenation of a double bond is a reduction
reaction. Ethene is reduced to ethane. Under
normal conditions, benzene resists hydrogenation.
It also resists the addition of a halogen or a
hydrogen halide. Under condition of high
temperature and high pressures of hydrogen, and
with certain catalysts, three molecules of
hydrogen gas can reduce one molecule of benzene
to form one molecule of cyclohexane.
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Ethers
An ether is a compound in which oxygen is bonded
to two carbon groups. The general structure of
an ether is R O R. The alkyl groups attached
to the ether linkage are named in alphabetical
order and are followed by the word ether. Some
ethers are non-symmetric, because the R groups
attached to the ether oxygen are different.
H   H H  H-C-O-C-C-H  
H   H H methyl ethyl ether
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Ethers
When both R groups are the same the ether is
symmetric. Symmetric ethers are named using the
prefix di-.
Diethyl ether
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Ethers
Diethyl ether
tert-butyl isopropyl ether
1,4-dioxahexylbenzene   
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Ethers
Diethyl ether was the first reliable general
anesthetic. Diethyl ether has been replaced by
other anesthetics such as halothan because it is
highly flammable and often causes nausea. Ethers
usually have lower boiling points than alcohols
of comparable molar mass. They have higher
boiling points than comparable hydrocarbons and
halocarbons. Ethers are more soluble in water
than hydrocarbons and halocarbons, but less
soluble than alcohols. This is because the O in
an ether is a hydrogen acceptor. Ethers form more
hydrogen bonds than hydrocarbons and halocarbons,
but fewer than alcohols.
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Questions
How are alcohols classified and named? Alcohols
are classified as primary, secondary, or
tertiary. They are named by dropping the e
ending of the parent alkane name and adding the
ending -0l How does the solubility of alcohols
vary with the length of the carbon
chains? Alcohols are soluble in water when the
carbon chain of the alcohol contains four or
fewer carbons. The solubility of longer chain
alcohols is much lower. How can functional groups
be introduced into organic molecules? By addition
or substitution reactions
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End of Section 23.2
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End of Chapter 23