Transcript Chapter 23

Chapter 23
Organic Chemistry
Contents and Concepts
1.
The Bonding of Carbon
Hydrocarbons
2. Alkanes and Cycloalkanes
3. Alkenes and Alkynes
4. Aromatic Hydrocarbons
5. Naming Hydrocarbons
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Derivatives of Hydrocarbons
6. Organic Compounds Containing Oxygen
7. Organic Compounds Containing Nitrogen
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Learning Objectives
1. The Bonding of Carbon
a. Describe the ways in which carbon typically
bonds.
b. Define saturated hydrocarbon, unsaturated
hydrocarbon, and aromatic hydrocarbon.
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Hydrocarbons
2. Alkanes and Cycloalkanes
a. Define alkane and cycloalkane.
b. Know the general formula of an alkane.
c. Give examples of alkanes in a homologous
series.
d. Define constitutional (structural) isomers.
e. Write a condensed structural formula.
f. Know the general formula of alkanes and
cycloalkanes.
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g. State the sources of alkanes and
cycloalkanes.
h. Predict the products of reactions of alkanes
with oxygen.
i. Predict the product of substitution reactions of
alkanes with the halogens F2, Cl2, and Br2.
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3. Alkenes and Alkynes
a. Know the general formula of alkenes (olefins).
b. Define geometric isomers.
c. Predict cis–trans isomers.
d. State Markownikoff’s rule.
e. Predict the major product of an addition
reaction.
f. Know the general formula of alkynes.
4. Aromatic Hydrocarbons
a. Recognize aromatic hydrocarbon molecules.
b. Predict the products of substitution reactions of
aromatic hydrocarbons.
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5. Naming Hydrocarbons
a. Learn the IUPAC rules for naming alkanes.
b. Write the IUPAC name of an alkane given the
structural formula.
c. Write the structural formula of an alkane
given the IUPAC name.
d. Learn the IUPAC rules for naming alkenes
and alkynes.
e. Write the IUPAC name of an alkene given the
structural formula.
f. Learn the nomenclature of aromatic
hydrocarbons.
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Derivatives of Hydrocarbons
6. Organic Compounds Containing Oxygen
a. Define functional group.
b. Recognize alcohols and ethers by functional
group.
c. Name alcohols using IUPAC rules.
d. Use common names for ethers.
e. Recognize aldehydes and ketones by
functional group.
f. Recognize carboxylic acids and esters by
functional group.
g. Name carboxylic acids and esters using
IUPAC rules.
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7. Organic Compounds Containing Nitrogen
a. Recognize amines and amides by
functional group.
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The Bonding of Carbon
Organic chemistry is the chemistry of compounds
containing carbon.
Because carbon can form single, double, and triple
bonds, the following bonding combinations are
possible for carbon:
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Hydrocarbons
The simplest organic compounds are made of
carbon and hydrogen. They are called
hydrocarbons.
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Three types of hydrocarbons exist.
Saturated hydrocarbons: contain only carbon–
carbon single bonds. They may be cyclic or acyclic.
Unsaturated hydrocarbons: contain at least one
carbon–carbon double or triple bonds.
Aromatic hydrocarbons: contain benzene rings or
similar features.
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Alkanes and Cycloalkanes
Alkanes are acyclic saturated hydrocarbons.
Cycloalkanes are cyclic saturated hydrocarbons.
The simplest alkane is methane. It can be
represented by its molecular formula , CH4,
or by its structural formula:
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Space−filling model of
methane
Ball−and−stick model of
methane with bond angles
Electrostatic potential map
of methane
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The Alkane Series
Alkanes are also called paraffins. They have the
general formula CnH2n+2. This general formula
gives no information about how the atoms are
connected, however.
We will assume that the carbons are bonded
together in a straight chain. These compounds are
called straight−chain or normal alkanes.
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The structural formulas for the first
four alkanes are shown to the
right.
These alkanes’ condensed
structural formulas are written as
follows:
Methane: CH4
Ethane: CH3CH3
Propane: CH3CH2CH3
Butane: CH3CH2CH2CH3
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The alkanes constitute a homologous series, a
series of compounds in which one compound
differs from a preceding one by a fixed group of
atoms.
Members of a homologous series have similar
properties that vary systematically, as shown in
Table 23.1.
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Constitutional Isomerism and Branched−Chain
Alkanes
In addition to straight−chain alkanes,
branched−chain alkanes are possible.
Isomers of butane are shown on the next slide.
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There are three constitutional isomers of pentane:
pentane (left), 2−methylbutane (center), and
2,2−dimethylpropane (right).
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Concept Check 23.1
In the model shown here,
C atoms are black and H
atoms are light blue.
a. Write the molecular
formula.
b. Write the condensed
structural formula.
a. C7H16
b. CH3CH2CH(CH3)CH(CH3)2
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Cycloalkanes
Cycloalkanes have the general formula CnH2n.
The first four members of this series are illustrated
on the next slide.
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Sources of Alkanes and Cycloalkanes
Petroleum, or crude oil, is a mixture of alkanes and
cycloalkanes with small amount of aromatic
hydrocarbons.
Crude oil from different regions differ in their
compositions of these compounds.
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Oil from the Canadian north slope contain
molecules composed of 20 to 40 carbon atoms.
Oil from Saudi Arabia contain molecules
composed of 5 to 20 carbon atoms. This oil is
more desirable as a source because it is easier to
transport crude oil containing low molecular mass
molecules.
Hydrocarbon mixtures in crude oil are separated
by a process known as fractional distillation. This
process separates molecules according to
molecular mass.
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Reactions of Alkanes with Oxygen
Alkanes react with oxygen exothermically to give
carbon dioxide and water.
Substitution Reactions of Alkanes
In a substitution reaction, a part of the reacting
molecule is substituted from a hydrogen atom on a
hydrocarbon or hydrocarbon group.
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Under the right conditions, alkanes can react with
other molecules.
For example, alkanes react with the halogens F2,
Cl2, and Br2. In the presence of chlorine and light
(hn) or heat, the following series of reactions
occurs:
CH4 + Cl2  CH3Cl + HCl
CH3Cl + Cl2  CH2Cl2 + HCl
CH2Cl2 + Cl2  CHCl3 + HCl
CHCl3 + Cl2  CCl4 + HCl
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Alkenes and Alkynes
Alkenes and alkynes are unsaturated
hydrocarbons.
Alkenes contain carbon–carbon double bonds.
They have the general formula CnH2n.
Alkynes contain carbon–carbon triple bonds. They
have the general formula CnH2n−2.
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Alkenes and Geometric Isomers
In an alkene, all of the atoms connected to the
double−bonded carbons are in one plane.
Rotation around the carbon–carbon double bond is
restricted due to the side−to−side overlap of the p
orbitals to form the p bond. This makes geometric
isomers—that is, cis and trans isomers—possible.
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This is illustrated below for 2−pentene.
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Oxidation Reactions of
Alkenes
Unsaturated
hydrocarbons can
undergo partial oxidation
under relatively mild
conditions. For example,
when KMnO4 is added to
an alkene or an alkyne,
the purple color of the
MnO4− ion fades and a
brown precipitate of MnO2
forms (as seen at right).
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Addition Reactions of Alkenes
Alkenes are more reactive than alkanes owing to
the presence of the double bond. Many reactions
add to the double bond.
In an addition reaction, parts of a reactant are
added to each carbon atom of a carbon–carbon
double bond, which converts it to a carbon–carbon
single bond.
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A simple example is the addition of a halogen,
such as bromine, Br2, to propene.
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Unsymmetrical reactants such as HBr and HCl add
to unsymmetrical alkenes to give two products.
2−bromopropane
1−bromopropane
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The two products are not formed in equal
amounts. Markovnikoff’s rule is a generalization
that states that the major product formed by the
addition of an unsymmetrical reactant, such as
H—Cl, H—Br, or H—OH, is the one obtained when
the hydrogen atom of the reactant adds to the
carbon atom of the multiple bond that has the
greater number of hydrogen atoms attached to it.
The major product is then 2−bromopropane.
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Alkynes
Alkynes are unsaturated hydrocarbons containing
a carbon–carbon triple bond. The general formula
is CnH2n−2.
The simplest alkyne is acetylene, C2H2. It is very
reactive with oxygen, so it is used in torches for
welding to give a very hot flame (~3000°C).
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Here acetylene
is prepared by
the reaction of
water with
calcium carbide,
CaC2.
The acetylene
produced burns
with a sooty
flame.
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Aromatic Hydrocarbons
Aromatic hydrocarbons usually contain benzene
rings: six−membered rings of carbon atoms with
alternating carbon–carbon single and carbon–
carbon double bonds.
The molecular orbital description of benzene
utilizes a p molecular orbital that is delocalized
across the entire molecule. The result is that the
double bonds in benzene do not behave as
isolated double bonds.
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A space−filling model of benzene.
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Some polycyclic aromatic hydrocarbons are shown
on the next slide.
Naphthalene is the simplest member of the series.
This white, crystalline substance is used in
manufacturing plastics and plasticizers (to keep
plastic pliable). Small amounts are used for
mothballs.
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The term aromatic indicates that compounds
containing a benzene ring have aromas. Flavoring
agents that can be made in the lab or are found in
nature and that contain benzene rings include
cinnamaldehyde, which is the source of the
cinnamon flavor, and methyl salicylate, which is
the source of the wintergreen flavor that is used in
candies and gum.
Benzene rings are also found in pain relievers
such as acetylsalicylic acid (aspirin),
acetaminophen (Tylenol), and the illegal drug
mescaline.
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Naming Hydrocarbons
1. Determine the longest continuous chain of
carbon atoms.
2. Name any chain branching off of the longest
chain as an alkyl.
3. Locate the branch on the longest chain by
counting the carbon to which it is attached so
that it has the lowest number possible.
4. For more than one of a group, use prefixes.
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?
Give the IUPAC name for each of the
following.
1
a.
2
b.
7 6 5
3
4
3
2
1
4
5
a.
b.
6
2−methylhexane
2,3−dimethyl−4−t−butylheptane
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?
Write the condensed structural formula of
2,3,5−trimethylhexane.
Hexane is a six−carbon chain.
2,3,5−Trimethyl means three methyl groups: one
each at the 2, 3, and 5 carbons.
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IUPAC Rules for Naming Alkenes and Alkynes
Identify the longest chain containing the multiple
bonds.
Alkenes have contain carbon−carbon double
bond(s) and alkynes contain carbon−carbon triple
bond(s).
The longest chain provides the stem name
followed by the ending –ene for alkenes or –yne
for alkynes.
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Number the longest chain from the end neared the
multiple bond. The multiple bond is given the
number of the first carbon atom involved in the
multiple bond. This number is written in front of the
alkene or alkyne name, separating the number
from the name by a dash.
Branched chains are named using the same
method used in naming alkanes.
If the multiple bond is in the middle of the longest
chain, number the chain from the end that gives
the branches the lowest number.
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The simplest alkene, CH2CH2, is ethene and has a
common name of ethylene.
The simplest alkyne, CHCH, is ethyne and has a
common name of acetylene.
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Concept Check 23.3
In the model shown here, C atoms are black and H
atoms are light blue.
a. Write the molecular formula.
b. Write the condensed structural formula.
c. Write the IUPAC name.
a. C5H10
b. CH3CH=CHCH2CH3
c. 2−pentene
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?
Give the IUPAC name for each of the
following compounds:
a. 2,4−dimethyl−2−hexene
b. 3−propyl−1−hexene
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?
Give the IUPAC name for each of
the following alkynes:
a. 1−propyne
b. 3−methyl−1−pentyne
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Nomenclature of Aromatic Hydrocarbons
Simple benzene compounds have one group
substituted on the benzene ring. They are named
by using the attached group name as the prefix.
For example, this compound is ethylbenzene:
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When two groups are on the benzene ring, the three
are isomers are named by the relative position of the
two groups. The following three isomers are called
ortho−dimethylbenzene or o−xylene (left);
meta−dimethylbenzene or m−xylene (center); and
para−dimethylbenzene or p−xylene (right).
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1−ethyl−3−methylbenzene
Numbers are also used to
show the positions of two
or more groups so that
they have the lowest
possible numbering.
1,3,5−trimethylbenzene
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It is also possible to treat a benzene ring as a
substituent using the prefix phenyl−.
This compound is diphenylmethane:
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Derivatives of Hydrocarbons
Certain groups of atoms in organic molecules are
especially reactive and have characteristic
chemical properties. A functional group is a
reactive portion of a molecule that undergoes
predictable reactions.
Table 23.7 lists some common functional groups.
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Alcohols and Ethers
We can think of an alcohol as a compound
obtained by substituting a hydroxyl group (—OH)
for a hydrogen atom (—H) on a tetrahedral (sp3
hybridized) carbon atom of a hydrocarbon group.
Alcohols are named by IUPAC rules similar to
those for naming the hydrocarbons, except the
stem name is the longest chain that contains the
—OH group and the name ends with the suffix −ol.
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?
Give the IUPAC name of the following
compound:
3−ethyl−3−hexanol
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Common Names of Ethers
Ethers have common names formed from the
hydrocarbon groups followed by the word ether.
The hydrocarbon groups are listed alphabetically.
For example, CH3OCH2CH2CH3, has a common
name of methyl propyl ether.
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?
Give the common name of each of the
following compounds:
a. CH3OCH3
b. CH3OCH2CH3
a. Dimethyl ether
b. Ethyl methyl ether
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Alcohols are classified according to the number of
carbon atoms attached to the carbon with the
hydroxyl group.
A primary alcohol has only one other carbon
bonded to the hydroxyl carbon.
A secondary alcohol has two other carbons
bonded to the hydroxyl carbon.
A tertiary alcohol has three other carbons bonded
to the hydroxyl carbon.
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An ether can be thought of as a derivative of an
alcohol in which the hydrogen of the hydroxyl
group is replaced with an alkyl group. Hydrocarbon
groups are symbolized by using the letter R.
R—O—H
An alcohol
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R—O—R
An ether
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Aldehydes and Ketones
A carbonyl group is composed of a
carbon–oxygen double bond (right).
An aldehyde is a compound that contains a
carbonyl group with at least one hydrogen
attached to it.
A ketone is a compound containing a carbonyl
group with two hydrocarbons attached to it.
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Some Aldehydes of Aromatic Hydrocarbons
Note: there
is also an
alcohol and
ether group.
Benzaldehyde
(oil of almond)
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Vanillin
(extract of
vanilla)
Cinnamaldehyde
(oil of cinnamon)
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Carboxylic Acids and Esters
A carboxylic acid is a compound that contains the
carboxyl group, —COOH.
An ester is a derivative of a carboxylic acid in
which the hydrogen of the carboxyl group is
replaced with an alkyl group. The ester, RCOOR,
is formed from the reaction of a carboxylic acid,
RCOOH, and an alcohol, ROH.
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IUPAC Names for Carboxylic Acids and Esters
Carboxylic acids are named by IUPAC rules like
those for aldehydes, except the ending on the
stem name is –oic followed by the word acid.
For example, the structure below is ethanoic acid.
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Organic Compounds Containing Nitrogen
Most organic bases are amines—that is,
compounds structurally derived by replacing one
or more of the hydrogen atoms of ammonia with
hydrocarbon groups.
A primary amine has replaced one hydrogen.
A secondary amine has replaced two hydrogens.
A tertiary amine has replaced all three hydrogens.
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Amines act as Brønsted−Lowry bases by
accepting a proton from water, producing a
derivative of an ammonium ion and the hydroxide
ion.
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Amides are compounds derived from the reaction
of ammonia or a primary or secondary amine with
a carboxylic acid.
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