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Chapter 10 Introduction to Organic Chemistry: Alkanes

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Functional Groups
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
1
Elements in Organic Compounds
In organic molecules,
carbon atoms bond
• with four bonds.
• mostly with H and
other C atoms.
• sometimes to O, N,
S,
• sometimes to
halogens F, Cl, and
Br.
2
Functional Groups
Functional groups are
• a characteristic feature of organic molecules
that behave in a predictable, similar way.
• composed of an atom or group of atoms.
• groups that replace a hydrogen atom in the
corresponding alkane.
• a way to classify families of organic
compounds.
3
Alkenes and Alkynes
Alkenes contain a
double bond between
adjacent carbon atoms.
(Double bond: 4 electrons)
Alkynes contain a triple
bond.
(Triple bond: 6 electrons)
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4
Organic compounds with
Carbon-Oxygen bonds
1. Alcohols
An alcohol contains the
hydroxyl (-OH)
functional group.
(instead of an H in that
place)
Ethanol
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OH- vs -OH
• OH- : hydroxide anion found in bases
(e.g NaOH)
• -OH: hydroxyl group colvalently bound to
carbon atom in an organic compound
(e.g. ethanol CH3-CH2OH)
6
2. Ethers
In an ether, an oxygen
atom is bonded to two
carbon atoms.
–C–O–C– .
has a common name
that gives the alkyl
names of the attached
groups followed by
ether.
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Diethyl ether
7
3. Aldehydes
An aldehyde contains a
carbonyl group (C=O),
which is a carbon atom
with a double bond to an
oxygen atom.
formaldehyde
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acetaldehyde
8
4. Ketones
In a ketone, the carbon of
the carbonyl group is
attached to two other
carbon atoms.
Acetone
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9
5. Carboxylic Acids and Esters
Carboxylic acids contain the
carboxyl group, which is a
carbonyl group attached to a
hydroxyl group.
O
║
— C—OH
Acetic acid
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10
5. Esters
An ester contains the carboxyl
group between carbon atoms.
Methyl acetate
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11
Organic compounds with CarbonNitrogen bonds
1. Amines
In amines, the functional
group is a nitrogen atom.
H
H
C —N – H or C —N —C
Methyl amine
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Dimethyl amine
12
2. Amides
In amides, the hydroxyl
group of a carboxylic acid is
replaced by a nitrogen
group (-NH2).
acetamide
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13
Functional Groups
Copyright © 2005 by
Pearson Education, Inc.
Publishing as Benjamin
Cummings
14
Learning Check
Classify each of the following as: alcohol, ether,
aldehyde, ketone, carboxylic acid, ester, amine or
amide.
1) CH3─CH2─CH2─OH
2) CH3─O─CH2─CH3
3) CH3─CH2─NH2
O
║
4) CH3─C─OH
carboxylic acid
alcohol
ether
amine
O
║
5) CH3─C─O─CH3
ester
15
Unsaturated Hydrocarbons
Cis-Trans Isomers
Chapter 11.2
16
Cis and Trans Isomers
In an alkene the double bond,
• is rigid.
• holds attached groups in fixed positions.
• makes cis/trans isomers possible.
CH3
CH = CH
cis
CH3
CH3
CH = CH
trans
CH3
17
Cis-Trans Isomers
In cis-trans isomers
• there is no rotation around
the double bond in alkenes.
• groups attached to the
double bond are fixed
relative to each other.
You can make a “double
bond” with your fingers with
both thumbs on the same
side or opposite from each
other.
18
Cis-Trans Isomers
Two isomers are possible when
groups are attached to the
double bond are different.
(a double bond cannot rotate)
• In a cis isomer, groups are
attached on the same side of
the double bond.
• In the trans isomer, the
groups are attached on
opposite sides.
19
Cis-Trans Isomerism
• Alkenes cannot have cis-trans isomers if a carbon
atom in the double bond is attached to identical
groups.
Identical
HH
C
HH
Identical
Brr
BH
Br
H
C
C
CH3
2-bromopropene
(not cis or trans)
H
C
Br
1,1 dibromoethene
(not cis or trans)
20
Cis-Trans Isomers in Nature
• Insects emit tiny quantities of pheromones, which are
chemicals that send messages.
• The silkworm moth attracts other moths by emitting
bombykol, which has one cis and one trans double
bond.
21
Organic Compounds with
Oxygen and Sulfur
12.1
Alcohols, Ethers, and Thiols
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Alcohols
An alcohol contains a hydroxyl group (—OH) attached to a
carbon chain.
A phenol contains a hydroxyl group (—OH) attached to a
benzene ring.
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Cummings
water
alcohol
phenol
23
Naming Alcohols
The names of alcohols
• in IUPAC replace the -e with -ol.
• with common names use the name of the alkyl group
followed by alcohol.
Formula
IUPAC
CH4
methane
CH3─OH
methanol
CH3─CH3
ethane
CH3─CH2─OH
ethanol
Common Name
methyl alcohol
ethyl alcohol
24
Classification of Alcohols
Classification of alcohols is
• determined by the number of alkyl groups attached to
the carbon bonded to the hydroxyl.
• primary (1°), secondary (2°), or tertiary(3).
Primary (1º)
1 group
H
|
CH3—C—OH
|
H
Secondary (2º)
Tertiary (3º)
2 groups
3 groups
CH3
CH3
|
|
CH3—C—OH
CH3—C—OH
|
|
H
CH3
25
Thiols
Thiols
• are carbon compounds that
contain a –SH group.
• are named in the IUPAC
system by adding thiol to
the alkane name of the
longest carbon chain.
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26
Thiols
Thiols
• often have
strong odors.
• are used to
detect gas leaks.
• are found in
onions, oysters,
and garlic.
27
Properties of Alcohols, Ethers,
and Thiols
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Boiling Points of Alcohols
Alcohols
• contain polar OH
groups.
• form hydrogen bonds
with other alcohol
molecules.
• have higher boiling
points than alkanes and
ethers of similar mass.
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29
Boiling Points of Ethers
Ethers
• do not have a polar
group.
• have an O atom,
but there is no H
attached.
• cannot form
hydrogen bonds
between ether
molecules.
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30
Solubility of Alcohols and Ethers
in Water
Alcohols and ethers
• are more soluble in water than alkanes because the
oxygen atom can hydrogen bond with water.
• with 1-4 C atoms are soluble, but not with 5 or more
C atoms.
31
Comparing Solubility and
Boiling Points
Molar
Compound
Mass
Alkane CH3─CH2─CH3 44
Ether
CH3─O─CH3
Alcohol CH3─CH2─OH
Boiling
Soluble
Point (°C) in Water?
-42
No
46
-23
Yes
46
78
Yes
32
Solubility of Phenol
Phenol
• is soluble in water.
• has a hydroxyl group that ionizes slightly (weak acid).
• is corrosive and irritating to skin.
OH
O
+ H2O
-
+ H3O+
33
Combustion of Alcohols
Alcohols undergo combustion with O2 to produce
CO2 and H2O.
2CH3OH + 3O2
2CO2 + 4H2O + Heat
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Oxidation and Reduction
In an oxidation,
• there is an increase in the number of C-O bonds.
• there is a loss of H.
In a reduction,
• there is an decrease in the number of C-O bonds.
• there is a gain of H.
35
Oxidation and Reduction
36
Oxidation of Primary (1)
Alcohols
When a primary alcohol is oxidized, [O],
• one H is removed from the –OH.
• another H is removed from the carbon bonded to the OH.
• an aldehyde is produced.
[O]
Primary alcohol
Aldehyde
OH
O
|
[O]
||
CH3—C—H
CH3—C—H + H2O
|
H
Ethanol
Ethanal
(ethyl alcohol)
(acetaldehyde)
37
Oxidation of Secondary (2)
Alcohols
When a secondary alcohol is oxidized, [O],
• one H is removed from the –OH.
• another H is removed from the carbon bonded to the OH.
• a ketone is produced.
[O]
secondary alcohol
ketone
OH
O
│
[O]
║
CH3─C─CH3
CH3─C─CH3 + H2O
│
H
isopropyl alcohol
dimethyl ketone
38
Oxidation of Tertiary Alcohols
Tertiary 3alcohols do not readily oxidize.
[O]
Tertiary alcohol
no reaction
OH
│
[O]
CH3─C─CH3
no product
│
CH3
no H on the C-OH to oxidize
2-methyl-2-propanol
39
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