NAME_______________________ PER
DATE DUE
ACTIVE LEARNING IN CHEMISTRY EDUCATION
CHAPTER 25
INTRODUCTION
TO ORGANIC
COMPOUNDS
(Part 1)
25-1
©1997, A.J. Girondi
SECTION 25.1
Introduction to Carbon Compounds
All substances can be classified as being either organic or inorganic. So far, our study of
chemistry has dealt mainly with inorganic compounds. Originally, organic substances were considered to
be those carbon compounds that were extracted from living things, while inorganic ones were
compounds that did not originate in living systems. An organic compound is defined as a substance that
contains the element carbon. However, some compounds that contain carbon are considered to be
inorganic. A better definition may be that organic compounds have a carbon base, that carbon is the
“backbone” of the compounds.
Organic chemistry plays a very important role in our daily lives. Many of the clothes we wear are
made of rayon, dacron, nylon and orion. These are all synthetic (man-made) organic compounds. Plastics
of all sorts are synthetic organic compounds, too. Petroleum is a naturally occurring organic substance,
but synthetic rubber and plastics are two of the by-products of petroleum.
A large number of modern chemical materials have been developed from by-products of
petroleum. In addition to these items, other materials such as sulfa drugs, penicillin, cortisone, perfumes,
detergents, vitamins, pesticides, anesthetics, and many of the more modern antibiotics are among the
contributions made to society through a study of organic chemistry.
Throughout the 18th century, early chemists unsuccessfully tried to synthesize organic
substances, starting with inorganic materials in their laboratories. Their failures gave rise to the “vital force
theory” which stated that organic compounds could only be produced by a “vital force” which was
responsible for life itself. This conclusion was closely tied to religious beliefs at the time. However, in
1828, the German chemist, Friedrich Wohier, succeeded in synthesizing an organic compound known as
urea, starting with two inorganic compounds. Thereafter, many other organic compounds were
synthesized in the same way in laboratories around the world. By 1850, the “vital force theory” was
discredited. From that time on, organic and inorganic chemistry were recognized as two major fields of the
science. There are over 90,000 known inorganic compounds. However, there are well over one million
known organic compounds, and many more are being synthesized by chemists every year!
Why are there so many organic compounds? Well, carbon atoms can attach themselves to each
other in wide variety of ways. They can join together to form short or long chains, and they can form rings
of many kinds, as well:
c-c-c
c
c-c-c-c-c-c
I
f
f
c-c-c-c-c
/\
c—c
II
c—c
El
Carbon Chains
\c—c/
I
Carbon Rings
The chains and rings can have branches and cross-links with atoms of other elements (mainly hydrogen)
attached to the carbon atoms. Different arrangements of carbon atoms correspond to different
compounds, and each compound has its own characteristic properties.
We are going to approach the subject of organic chemistry in terms of organic nomenclature.
Nomenclature involves the naming of compounds. We will restrict ourselves to the simpler organic
compounds, because the more complex ones can get really complicated. You will be given a set of rules
to follow as you name compounds. These rules must be followed very carefully. Success in learning
organic nomenclature will involve some memorization on your part, but it will rely mainly on a logical
approach to the problems presented.
The second most abundant element found in organic compounds is hydrogen. This chapter will
deal exclusively with compounds composed of only carbon and hydrogen.
These are called
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©1997, A.J. Girondi
___________
hydrocarbons. These two elements can combine in countless ways. The structures of some
hydrocarbons are shown below. The lines between the atomic symbols represent bonds. There are
three types of carbon to carbon bonds:
HH
H
H
c
H-C-C-H
H
IiI+IiI
single bondj
In each case you will note that carbon has a total of four bonds. This is because carbon
has four valence electrons. There are only a few carbon compounds in which carbon
does not have four bonds. One example is carbon monoxide. In this chapter,
however, we will deal only with organic compounds in which the carbon atoms have
four bonds. After we have studied the hydrocarbons, Chapters 26 and 27 will
introduce you to the names and structures of organic compounds which contain other
elements in addition to carbon and hydrogen.
Section 25.2
:CQ:
carbon
monoxide
The Alkanes
The alkane family represents the simplest of the hydrocarbons. The general formula for the
compounds in this family is CnH2n+2, where “n” equals the number of carbon atoms in the molecule. For
example, if you substitute a I into this formula you will get CH4. Substitute a 2 and you will get C2H6.
These are the first two members of the family. The compounds in the alkane family are often called
saturated compounds, which means that the molecules contain only single bonds between the carbon
atoms.
Naming alkanes is fairly simple. The prefix in the name of each compound indicates the number of
carbon atoms present. All alkanes have a suffix of -ane. A list of alkane prefixes is shown in Problem I
which has been partially completed for you. To make writing formulas or drawing structures easier, the
hydrogens on the carbons are not always shown (note the structures on page 25-3); however, you should
assume that enough hydrogen atoms are present to give each carbon atom 4 bonds.
Problem 1. Give the name and molecular formula for each compound below. Use the formula CnH2n+2
to determine the formula, and add the suffix “ane” to the prefixes to obtain the names.
Prefix
No. of Carbons
Name
Molecular Formula
a.
meth-
I
methane
CH4
b.
eth-
2
c.
prop-
3
d.
but-
4
e.
pent-
5
f.
hex-
6
g.
hept-
7
C3H8
pentane
C
1’
-
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©1997, A.J. Girondi
____C4H1o
______CH4
______________
__
__________
__________
__________
__________
__________
_________________
__________
h.
oct-
8
I.
non-
9
j.
dee-
10
Cja_._
In problem 1, you were writing molecularformulas. The kinds of formulas seen at the top of page
25-4 are known as structural formulas. Writing structural formulas for organic compounds can become very
cumbersome when all of the chemical bonds are included in the drawings. To remedy this problem,
chemists have developed a shorthand method of writing structural formulas that involves condensing the
structures. In this shorthand method, the carbon atoms are still written separately (separated by hyphens),
but the hydrogens which are bound to carbons are not. Instead, the hydrogens are written to the right of
the carbon atoms to which they are bonded. This method of representing organic compounds is known
as the condensed structural formula. Study the examples of condensed structural formulas below.
Compound
Molecular Formula
Condensed Structural Formula
Structural Formula
H
methane
CH4
CH4
HC—H
H
HHHH
butane
C4HI0
CH3-CH2-CH2-CH3
H —C—C—C—C— H
HHHH
Problem 2. Complete the exercise below.
Compound Name
Condensed Structural Formula
Molecular Formula
a. methane
b. ethane
C
c.
propane
d. butane
e. pentane
LCt C&f.
3
C.’c\Q-\
hexane
(l
1’
-.
g. heptane
‘—-
I”
-.
(d.
,
I
h. octane
i. nonane
j. decane
(L
25-5
3
cLC}zCi\
©1997, A.J. Girondi
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__________
___________
Section 25.3
AIkyl Groups
Carbon chains are not rigid structures. They can bend and flex freely. When we say that an alkane
has a “straight” chain, we don’t really mean straight. We mean that it is a continuous chain, rather than a
branched chain. The two structures below both contain six carbon atoms. The one on the left is
“straight,” while the one on the right is branched.
CH3
CH3— CH2— CH2— CH— CH3
CH2— CH2— CH2
CH3
CH2— CH3
This is a branched
chain of carbon atoms.
This is one continuous
chain of carbon atoms.
Now that you have mastered the straight-chain (or should we say “continuous” chain) alkanes, it is
time to try something more challenging. Most alkanes exist as “branched” molecules such as the one
shown below. The longest continuous chain of carbon atoms in the molecule below is 7 (enclosed by
box). Therefore, the parent compound here is heptane. (Remember, the longest continuous chain is not
necessarily straight!)
CH2— CH3
3
CH3— CH2— CH2— CH— CH-. J
CH2— CH3
The longest continuous chain contains 7 carbon’s.
Having identified the parent compound, we must next identify the side chains. These side chains are
commonly called alkyl groups. AlkyJ groups are attached to the longest continuous chain. When written
alone, they are usually shown with a free-bonding site represented by a dash (like this: —CH3). This
bonding site represents a spot where a hydrogen atom has been removed. Thus, the general formula for
the alkyl groups is CnH2n÷i. The free bonding site is what allows the alkyl group to bond to the parent
compound. Alkyl groups are named with the same prefixes as the alkanes themselves. The suffix is
changed from “ane” to “yl.” Complete Problem 3 below by entering the formulas and condensed
structural formulas of the first six alkyl groups.
Problem 3. Complete the exercise below.
a.
Name of Alkyl group
Condensed Structural Formula
methyl
-CH
-ct_ -c’
b.
c.
d.
e.
f.
butyl
-CHHQHcHs
3
LC?J L(’AC4
C U\
2
-C.i -C
2
3
Cz -C\\
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©1997, A.J. Girondi
___________
Depending on where the hydrogen atom is removed, the bonding site on some alkyl groups can change
position. This would change the way in which the alkyl group bonds to the parent compound. For
example, note the two alkyl groups shown below. Both are composed of three-carbon chains, but the
bonding site differs:
—
CH3— CII— CH3
isopropyl
CH— CH2— CH3
propyl
The compound on the left below has a propyl group attached to the parent compound which is octane.
The compound on the right has an isopropyl group attached to the parent compound (heptane). Note
that all carbons in the molecules have four bonds.
CH3
CH2
CH2
I
CH3—CH2—CH2—CH—CH2—CH2—CH2—CH3
CH3— CH— CH3
I
CH3CH2—CH2—CH—CH2CH2—CH2—CH3
Propyl group attached to an 8-carbon chain
isopropyl group attached to an 8-carbon chain
The carbon atoms on the end of the chain are called terminal carbons. When the bonding site of an alkyl
group occurs on a terminal carbon, the alkyl group is said to be “normal” and its name is sometimes
preceded by the letter n. Thus, the propyl group above could also be called n-propyl (pronounced
“normal propyl”). We will consider the use of this “n” prefix as optional. The other structure with the
bonding site on the center carbon is called isopropyl.
SECTION 25.4
IUPAC Rules for Naming Alkanes
A system for naming organic compounds has been developed by the International Union of Pure
and Applied Chemists (IUPAC). The system is accepted and used throughout the world. There is also a
method by which many organic compounds are given “common” names, but we will use only the IUPAC
system in this chapter. We will consider the rules one at a time and apply them to some practice problems.
RULE 1: Locate the longest continuous chain of carbon atoms. This will give you the name of the
“parent” compound.
For example, if the longest chain contains four carbons, the parent compound is butane. The longest
chains in the following two molecules are enclosed by a box:
CH2— CH3
CH3
CH3-F CH— CH2— CH— CH2— CH2— CH3
I
CH2
ICH2CH3I
CH2
CH3—CH2
CH— CH2— CH2— CHI CH2— CH3
/0
longest continuous chain = 8 carbons
-
1 CH2—CH2—CH2—CH3I
longest continuous chain = 11 carbons
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©1997, A.J. Giroridi
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Problem 4. Draw a box around the longest continuous chain of carbon atoms in the structures below,
and name the parent compound for each one.
CH3
a
CH3— CH2
—
‘CH3
CH2— CH— CH3
b.
c.
CH3—CH
cHa— QH2CH
CH3
CH2— CH2— CHi’
ICH2— CH3
d
CH2— CH3
CH3
e
CH3—CH—CH2—CH—CH3
f.
CH3—CH—CH2—CH3
CH2- CH3
1
CH3—C—CH2--CH3
CH
CH2— CH3
a. parent:
d. parent:
b. parent:
e. parent:
c. parent:
f. parent:
c’:
-
RULE 2: The name of the parent compound is modified by noting what alkyl groups are attached to the
chain. Number the longest chain so that the alkyl group(s) will be on the lowest numbered carbons.
Note in the molecules shown below, that the longest chain should be numbered from right to left
in order to give the carbon which is bonded to the methyl group the lowest possible number:
1
2
3
4
4
3
2
1
CH3— CH2— CH— CH3
CH3— CH2— CH— CH3
CH3
Incorrect Numbering
CH3
Correct Numbering
The correct name of this compound is 2-methylbutane. The “2-” indicates that the methyl group is
attached to the second carbon in the longest chain. Note that the name of the alkyl group is added to that
of the parent compound (butane) to form one word, and that hyphens are used to separate numbers from
alphabetical parts of the name.
Problem 5. For the following compounds, draw a box around the longest continuous carbon chain and
name each molecule. The name of the molecule in part “b” is given to help you.
a.
CH3—CH-CH2—CH2--CH3,
Name:
b.
CH3— CH2— CH2— CH— CH2— CH3
Name:
0
\‘
\\
3-ethyihexane
CH3— CH2
25-8
©1997, A.J. Girondi
CH2—CH2—CH3
I
c.
-
-‘f
CH3—Ch2CH2—CH2—CH—CH2—CH2— CH3.
JL
1
‘
Name:
(
‘0
CH3— CH— CH3
d CH3—CH2— CH2— CH— CH2— CH2— CH2— CH2— CH3
Name:
-
9
RULE 3: When the same alkyl group occurs more than once in a molecule, the numbers of the carbons to
which they are attached are all included in the name. The number of the carbon is repeated asmanytimes
as the group appears. The number of repeating alkyl groups is indicated in the name by the use of Greek
prefixes for 2, 3, 4, 5, etc. (di, tn, tetra, penta, etc.).
To better understand rule 3, study the following examples.
F H3
is called 2,3-dimethylpentane
CH3—CH —CH— CH2— CH3
CH3
Note that numbers used in the name are separated from each other by commas, and note that the
numbers are separated from the rest of the name with a hyphen.
CH2—CH3
is called 3,3-diethyihexane
CH3— CH2— CH2— C— CH2— CH3
CH2— CH3
Problem 6. Name the four molecules whose structures are drawn below.
CH2— CH3
CH3
a
CH3C-j3
CH3
CH2— CH3
I
b. CH3—C—CH3
\CH3
c.
H3
CH2
CH2
CH2CH2CCH2CH2CH3
CH2— CH3
a.
d.
CH3— CH— CH2— CH2—CH3
b.
S.
CH- CH3
CH3— CHCH3
d
-CA(U
c.
eccftC
d.
1)
25-9
©1997, A.J. Girondi
RULE 4: If there are two or more different kinds of alkyl groups attached to the parent chain, name them in
alphabetical order.
CH2— CH3
I
is called 3-ethyl-2-methylpentane
For example:
CH3— CH— CH— CH2 CH3
It is NOT called 2-methyl-3-ethylpentane
CH3
However, when you are determining the alphabetical order, do i consider any Greek prefixes that are
being used. For example:
CH3
CH2—CH3
CH3— C— CH2— CH
is called 4-ethyl-2,2-dimethylheptane
CH2— CH2— CH3
—
It is NOT called 2,2-dimethyl-4-ethylheptane
CH3
Problem 7. Name the four molecules drawn below.
_c
(
CH3_
a.
CH2— CH2—
CH3
CH3
I
b.
‘
i
CH3— CH2-- 00H2
CH2-CH3
V
2
CH2—CH2—CH3
[ç
CH2— CH— CH2
CH2— CH3
CH3
0
c0flocc
‘
O
CH2— CH3
c.
CH3— CH2— OH— CH— CH2— 0H
CH3-CH- CH3
CH3
CH3
0
0
CH3
CH3
l
I
Z>
i
d. CH3—CH—CH2—CH-CH2OH2CHCH3
-
CH2-CH3
Vc
RULE 5: To put the finishing touches on the name of an alkane, keep the following points in mind: (a)
hyphens are used to separate numbers from names of substituents; (b) numbers are separated from each
other by commas; (c)the last alkyl group to be named is prefixed to the name of the parent alkane, forming
one word; and (d) the suffix “-ane” indicates that the molecule is an alkane.
ACTIVITY 25.5
Using Molecular Models
The structure of alkanes is more understandable if you see them in three dimensions. We will use
molecular model kits for this purpose. Obtain a box containing a molecular model kit and determine which
parts represent carbon atoms, hydrogen atoms, carbon to carbon bonds, and carbon to hydrogen bonds.
When you have done this, assemble models of the six molecules drawn in Problem 4. Pick up one of your
25-10
©1997, A.J. Girondi
models and rotate one section of the model while holding the other. Do you see how rotation is possible
Holding the model with both hands, bend and flex it a bit. Note
around a single bond?
the bond angles betweeh he carbons themselves and between the carbons and the hydrogens. Do you
see why these molecules are not really “straight” chains? C>
.
Because free rotation is possible around a single bond, what can you conclude about the 2 molecules
If you named these two molecules, what would
shown below?iy
-
What is the name’{3)
you discover’ {2}
CH
CH3—CH— CH2— CH— CH3
I
CH3
CH3—CH— CH2— CH— CH3
SECTION 25.6
I
I
CH3
CH3
Cyclic Alkanes
The compounds we have studied so far have been either “straight” or “branched” chains. Carbon
atoms can also form rings which result in the formation of cyclic alkane molecules with the general formula,
CnH2n. Naming the cyclic alkanes is not difficult, but the rules do differ a bit from those used to name the
straight and branched chained compounds.
The name of a cyclic molecule requires the addition of the prefix “cyclo” to the name of the
hydrocarbon. Note the two condensed structural formulas below.
CH2
CH2— CH2
CH2— CH2
CH2— CH2
cyclopropane
cyclobutane
/\
I
I
To make cyclic compounds easier to draw, a shorthand notation is used in which the hydrogens and
carbons which are part of the ring are not represented at all. The rings are represented by lines, and a
carbon atom is assumed to be present at each angle in the ring. The proper number of hydrogen atoms is
assumed to be attached to each carbon.
For example:
cyclopropane
cyclobutane
cyclopentane
cyclohexane
C3H6
C4H8
C5HIO
C6Hi2
Name this compound
U
{4}
25-11
©1997, A.J. Girondi
Like the “straight-chained” compounds, cyclic molecules can also contain alkyl side chains. The
same general rules for alkane nomenclature apply to the cyclics, except that all positions in a ring are
equivalent, so a number is not needed to indicate the position of the alkyl group there is only onealkyl
group on the ring. For example:
CH3
—
This is called methylcyclohexane
(It is NOT called 1-methylcyclohexane)
The carbon on which the alkyl group is located is automatically assumed to be number I.
Problem 8. Name the cyclic molecules below.
CH3— CH2
CH3
CH2
ccET
b.
‘.
a
(X
\.f\’:’
If there are two or more substituents on a ring, numbers must be used to indicate their positions.
One of the substituents is always assigned position number 1, and starting at position I, the chain is
numbered either clockwise or counterclockwise so as to give the other substituents on the ring the
smallest possible numbers. For example:
CH3
This is called I-ethyl-2-methylcyclopentane
CH2— CH3
This is called I ,2-dimethylcyclopentane
CH3
(It is NOT called I ,5-dimethylcyclopentane)
CH3
(You may have wanted to call it 4-ethyl-I-methylcyclohexane,
but we chose to assign the number I position to ethyl since it
comes first, alphabetically, and since we get the same
numbers,1 and 4, either way.)
CH3—
CH3— CH2—ç’
This is called 1-ethyl-4-methylcyclohexane
CH
—
This is called 4-ethyl-I ,2-dimethylcyclopentane
CH3
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©1997, A.J. Girondi
__
In the last example, we assign position 1 to the carbon in the lower right corner and number the ring
counterclockwise. This gives the lowest possible set of numbers for the three substitutents on the ring.
CH2—CH3
CH3
This is called 3-ethyl-1,1,2-trimethylcyciobutarie
(We numbered clockwise this time)
CI
CH3
In the molecule drawn above, if we assigned position #1 to the carbon which is bonded to the ethyl group,
we would have had to number counterclockwise and name the molecule: 1-ethyl-2,3,3-trimethylbutane.
This was avoided because it resulted in higher numbers.
2 ••(—c:
The three structures drawn below are identical. Write the name: {5’i
CH3
CH3
CH3
CH3
CH3
Problem 9. Name the cyclic alkanes shown below:
CH2—CH3
a. CH3—CH2—CH3
d.
CH3
b.
A
CH2— CH3
_ACH
3
CH
CH2— CH3
CH2—CH3
CH3
e.
CH
CH3Q CH3
f.
CH3
CH3
a.
.54ucoc
g.
CH3
-
,‘
i
c(\Q(
\
b.
•
c.
g.
d. ‘ ,2
C
CH2— CH2— CH3
cOxka(’L
2..
s&
4
0
25-13
©1997, A.J. Girondi
Models of Cyclic Alkanes
ACTIVITY 25.7
Using a molecular model kit, construct the four cyclic molecules drawn below. The models give
you some idea of what these cyclic compounds look like in three dimensions. You will also see the effects
of the bond angles on the shapes of the molecules. Be sure to include all needed hydrogen atoms, even
if they are not shown on the drawings.
cyclopropane
C3H6
cyclobutane
cyclopentane
cyclohexane
C4H8
C5HIO
C6H12
Do any of these cyclic compounds have what you might consider to be f rings? If so, which one(s)?
(6}
Here is a summary of the rules used to name alkanes:
RULE 1: Locate the longest continuous chain of carbon atoms. This will give you the name of the
“parent” compound.
RULE 2: The name of the parent compound is modified by noting what alkyl groups are attached to the
chain. Number the longest chain so that the alkyl group(s) will be on the lowest numbered carbons.
RULE 3: When the same alkyl group occurs more than once in a molecule, the numbers of the carbons to
which they are attached are all included in the name. The number of the carbon is repeated as many times
as the group appears. The number of repeating alkyl groups is indicated in the name by the use of Greek
prefixes for 2, 3, 4, 5, etc. (di, tn, tetra, penta, etc.).
RULE 4: If there are two or more different kinds of alkyl groups attached to the parent chain, name them in
alphabetical order.
RULE 5: The put the finishing touches on the name of an alkane, keep the following points in mind: (a)
hyphens are used to separate numbers from names of substitutents; (b) numbers are separated from
each other by commas; (c) the last alkyl group to be named is prefixed to the name of the parent alkane,
forming one word; and (d) the suffix “-ane” indicates that the molecule is an alkane.
SECTION 25.8
Naming Alkenes
Now that you are an expert on alkanes, let’s take a look at the alkene functional group. A
functional group is a feature of a class of compounds that is responsible for its characteristic properties.
The functional group of the alkanes is the single bond. The functional group of the alkenes is the double
bond. Alkenes contain at least one double bond which exists between a pair of carbon atoms. The
general formula for the straight-chained alkenes is CnH2n. The suffix to be used in the names of alkenes is
“-ene.” The rules for naming alkenes are the same as those for alkanes with a few additional restrictions.
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©1997, A.J. Girondi
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Additional Rules for the Nomenclature of Alkenes:
RULE 1: The chain chosen as the parent chain must contain the carbon—carbon double bond (C=C).
RULE 2: The parent chain must be numbered to give the carbon-carbon double bond the lowest possible
number.
RULE 3: The name of the alkene must contain a number to indicate the position of the double bond.
Note the example below. The longest carbon chain alkene is numbered correctly, giving the double bond
the lowest possible number.
1
2
7
4
5
6
CH2— CH3
I
CH3— CH2—CH—CH= C— CH3
3
CH3
3,5-dimethyl-3-heptene
As we number the carbons, the first carbon involved in the
double bond is #3, so the parent chain is called 3-heptene.
Methyl groups are located on carbons #3 and #5.
A number is not used to locate the double bond in chains which are shorter than four carbons. Two
examples are below.
This is called ethene, not 1-ethene
‘—
CH2= CH2
CH3— CH= CH2
This is called propene, 1-propene
Why is it that these two molecules do not require the use of the number? (7)_—
(
‘
Problem 10. Name the alkenes below. After you have located the longest chain containing the double
bond, be sure to number the chain so that the double bond gets the lowest possible number.
t—
.
a
a. CH3—CH2—CHCH2
‘)
3
b. CH3-CH=CH—CH3
;
3
c. CH3—CH2-CH= CH—CH3
‘
3
*
d. CH3—CH2—CHCH-CH2-CH3
—
--
,
e\
e. CH2= CH2
f. CH3—CH=CH2
CH3
13
CH3— CH— CH2— Cl-I-- CH= Cl-12
-
g.
-Ux€ftL
3
)
CH3
25-15
©1997, A,J. Girondi
h.
CH3—c=cH— CH&
CH2—CH3J
i.
M-2
4Lc
-‘
CH3—CH—CH=CH2
rr-
CH3
1- xc €e
L
-
j. (CH— CHZ CH— C— CH2— CH3
L4
CH2— CH3
SECTION 25.9 Naming Cycloalkenes
Cycloalkenes are named similarly to straight chained alkenes. The carbons in the ring that contain
the double bond are always assigned the #1 and #2 positions, so numbers are used only to locate the
positions of substitutents attached to the ring - not to locate the position of the double bond. The general
formula for cyclic alkenes in CnH2n-2. Study the examples below.
CH3
CH3
CH3
3-methylcyclohexene
cyclobutene
3,4-dimethylcyclopentene
Problem 11. Name the following cycloalkenes.
4%_
a.
CH2— CH3
L
\(
t)
‘
CH3
I
b.
flCH
3
CH3— CH2
r’3
c.
\rnccjc*c,1c
CH3
25-16
©1997, A.J. Girondi
_____
CH3—CH— CH3
d.
A
CH2— CH2— CH3
e.
Oj
CH3
CH3
CH2—CH3
f.
2bk 3-clo biec
2-
CH2— CH2— CH2— CH3
SECTION 25.10
Naming Alkynes
The functional group of the compounds known as the alkynes is a jpe bond. The general
formula for straight-chained alkynes is CnH2n-2. Alkynes are named in much the same way as the alkenes,
except that their names end with the suffix “-yne”, signifying the triple bond. Once again, the triple bond
must be located within the parent chain, and it should be assigned the lowest possible number.
Additional Rules for the Nomenclature of Alkynes:
RULE 1: The chain chosen as the parent chain must contain the carbon- carbon triple bond.
RULE 2: The parent chain must be numbered to give the carbon-carbon triple bond the lowest possible
number.
RULE 3: The name of the alkyne must contain a number to indicate the position of the triple bond.
As was the case with the alkenes, no number is used to locate the triple bond if the parent chain is shorter
than four carbons:
CHE CH
CHE C— CH3
CHE C— CH2—CH3
CH3— CE C— CH3
ethyne
propyne
I -butyne
2-butyne
1
For the example at right, the correct name is 5-methyl-2-hexyne
25-17
2
CH3— C
—
34
56
C— CH2— C— CH3
I
CH3
©1997, A.J. Girondi
Problem 12. Name the alkynes drawn below. Be sure to number the parent chain so as to give the
triple bond the lowest possible number.
a. CHE C-CH2-CH2-CH3
—CL’
b. CH3-CH2-CH2-CEC-CH3
c. CH3-CH2-CE C-CH3
•i
‘—
d. CH3—CH2-CH2—CECH
Z
I
e. CH3-CE C—CH2--CH2-CH2-CH3
L
\
Y\L
\-
pECF-
\CH— CH
f.
\)%k
CH3
CH3
CH3
g.
CH2— CH— CH
‘1Q:rQ
CE CH
CH2— CH3
CH3
-s.
CHEC—C—CH3
h.
CH2—CH2—CH3
CH3
5
I___L.
CH3—CEC--CH—CH2—CH—CH3
1-.
-
CH2— CH2
?c
2p\ftQ
CH3
Table 25.1
Summary of General Formulas for
Alkanes, Alkenes, and Alkynes
General Formula
Class of Compound
CnH2n÷2
CnH2n
CnH2n
CnH2n-2
CnH2n-2
Straight-chained alkanes
Cycloalkanes
Alkenes
Cycloalkenes
Alkynes
25-18
©1997, A.J. Girondi
SECTION 25.11
Review Problems
Problem
13. The names of the compounds listed below are NOT correct. Using the incorrect name,
draw the structural formula in the work area. Then write the correct name of each compound on the line
provided.
a. 4,4-dimethyihexane
Work Area
Correct Name
Incorrect Name
)3
(-C-c-c -(-C
lQ
kQ
c
3
C-
i:
C\
(-
QC\&
b. 2-ri-propylpentane
—
c. 1,1-diethylbutane
(_C
d. I ,4-dimethylcyclobutane
J
()
(
e. 3-methyl-2-butene
2-n--24çA(( &
C
—c
-
c-c
f.
g. 2-t-propyl-I-propene
-
y.
5-ethylcyclopentene
2 -(ruL%—V
-t
‘
(
h. 2-isopropyl-3-heptene
2)A-
-
ocec&
2.
I.
C — C —C
2,2-dimethyl-3-butyne
C
j. 5-octyne
(-C-C-C”CEC-C-C
25-19
©1997, A.J. Girondi
Problem 14. Write condensed structural formulas for the following:
Condensed Structural Formula
Name
— C
3
Gk
-(
- C— C}- C
2
C—C\
a. 4-isopropyloctane
Ci-\
3
CA\
3
cCH—CCC
b. 3,4-dimethyl-4.
n-propylheptane
4
3
cI
_L.
c: 1,1-dimethylcyclobutane
CkjCi\
2
-c-V
(c- CL—C- 3
d. 3-ethyl-3-heptene
S3
e. 3-ethyl-2-methyl-1-hexene
C;R-C_c
f. 3-octene
=
C4 2
(-
g. 3,3-dimethyl-1-butyne
—
(
—
3
c\k c-C:\
2
CU
2
—
h. 4,4-dimethyl-2-pentyne
(çJ
i.
3-i-butyl-2-ethylcyclohexene
3
j. 3,4-diethyl-4,6-dimethylnonane
C\4
c— C
C4aCAA.
25-20
C
2
CA--C- (‘
©1997, A.J. Girondi
SECTION 25.12
Learning Outcomes
Before leaving this chapter, read through the learning outcomes listed below. Place a check
before each outcome when you feel you have mastered it. When you have completed this task, arrange
to take any quizzes or exams on this chapter, and move on to Chapter 26.
1. Distinguish between organic and inorganic compounds.
2. Distinguish between alkanes, alkenes, and alkynes.
3. Determine the number of carbon atoms in the longest chain of any alkane, alkene, or alkyne.
4. Use the IUPAC system to name alkanes, alkenes, and alkynes, given their condensed structural
formulas.
5. Given the IUPAC names, be able to draw condensed structural formulas for alkanes, alkenes,
and alkynes.
25-21
©1997, A.J. Girondi
NAME___________________________ PER
DATE DUE
ACTIVE LEARNING I N CHEMISTRY EDUCATION
CHAPTER 26
iNTRODUCTiON
TO ORGANiC
COMPOUNDS
(Part 2)
26—1
©1997, A.J. Girondi
SECTION 26.1
Alcohols
Alcohols are molecules in which an alkyl group is attached to a hydroxy group (—OH). The
hydroxy group is responsible for the characteristic properties of alcohols so we refer to it as the functional
group for alcohols. There are three different methods for naming alcohols, but we will use only the IUPAC
system. The rules that you used for naming alkanes and alkenes (in Chapter 25) are similar to those used
for the alcohols. The modified rules are listed below.
Additional Rules for the Nomenclature of Alcohols:
RULE 1: Locate the longest continuous chain of carbon atoms which contains the “hydroxy” (—OH)
group. This chain will serve to identify the parent compound.
RULE 2: Number the chain so as to give the carbon atom which is bonded to the —OH group the lowest
possible number.
RULE 3: A number is included before the name of the parent compound to indicate the position of the
—OH group.
RULE 4: The suffix “ol” is added to the name to indicate that the molecule is an alcohol.
Study the examples below. Note that the number indicating the position of the —OH group is not used if
the chain is shorter than 3 carbons. Why?
{1)
-
—tDA
Cc’.
Condensed Stnictural Formula
Name
Formula
methanol
CH3OH
CH3
ethanol
CH3CH2OH
CH3— CH2
OH
OH
1-propanol
CH3CH2CH2OH
CH3— CH2— CH2— OH
2—propanol
CH3CHOHCH3
CH3— CH— CH3
/C\
H
H\
OH
cyclopentanol
H\/OH
26—3
©1997, A.J. Girondi
___OH
In addition, you see in the example above that the position of the —OH (“hydroxy”) group is not included in
the names of cyclic alcohols, either. Why not? (Remember that this is also the case for the double bond
)
2
in cyclic alkenes.{
- The hydroxy group has
1
(The hydroxy group,—OH, should not be confused with the hydroxide ion, OH
the same formula, but it is not an ion.)
Problem 1. Name the alcohols given below.
I
)
a.
CH3—CH2--CH—CH2--CH3
OH
b.
2-.
CH3—CH—CH2-CHS
OH
CH3
c.
A
CH—CH—H3
-CH
3
OH
CH3
OH
d.
N\c. H,
CH3—CH-CH2--CH--CH-CH3
CH3
L4
e.
\\\
CH3-CH2-CH—CH2--CH2--CH2-OH
I
\N
CH2— CH3
cIc
5
C
( fl C
‘I
OH
g.
CH3
‘31 -cc
h.
Cu
CH3_OQH
CH3
OH
N
I.
CH3—— CH2— CH3
26-4
©1997, A.J. Girondi
OH
J.
CH3-CH-CH3
This compound is commonly called “rubbing
alcohol.” Give its IUPAC name.
Problem 2. Draw the condensed structural formulas for the following.
b. cyclopropanol
a. 4,4—dimethyl—2—hexanol
3
c
C\ ( •C\kZCt:\
3
C
I—’
d. 3,4—diethyl—2—heptanol
c. 2,3—diethylcyclohexanol
(A
CIcj C
CC
C’ (i
C -C’
2 (C3
3
CCJc
Section 26,2
Ethers
Ethers are compounds which contain an oxygen atom bonded to two carbon atoms within the
carbon chain. The functional group is the C—O—C arrangement found within the chain. When you look at
For example,
an ether molecule, you will see an alkyl group on each side of the oxygen.
on
the right. The
group
methyl
and
a
atom
the
oxygen
left
the
of
on
ethyl
group
has
an
CH3—CH2--O—CH3
used
frequently
still
are
names
common
Although
“common name” for this molecule is methyl ethyl ether.
for ethers, we will stick to our “game plan” and use the IUPAC system.
Parent compound is “ethyl”
T
H
O_CH
C
3
‘CH
L
2
Functional group is “methoxy”j
In the IUPAC system, the larger of the two alkyl groups attached to the oxygen is considered to be
the parent compound. For the ether mentioned in the last paragraph above, the parent compound would
be ethane. The smaller alkyl group and the oxygen atom are considered to be a substituent group on the
parent compound. The —O—CH3 group is the substituent and it is called “methoxy.” So the name of that
ether is methoxyethane. If the substituent had been CH3—CH2--O—, it would have been called “ethoxy.”
Collectively these functional groups of the ethers are known as alkoxy groups. Only one modified rule
needs to be mentioned here regarding the nomenclature of ethers.
26—5
©1997, A.J. Girondi
Additional Rule for the Nomenclature of Ethers:
RULE: For ethers with parent chains that contain 3 or more carbon atoms, a number is included to
indicate the position of the alkoxy group.
Study the examples below.
CH3
CH3-O--CH-CH3
2—methoxypropane
CH3-O-CH2-CH2-CH3
1 —methoxypropane
CH3-CH--O-CH 2-CH3
ethoxyethane
CH3-O--CH3
methoxymethane
Problem 3. Name the following ethers:
Z.
L
a.
CH3-O-CH2--CH2--CH2-CH3
b.
CH—CH--CH2--O-CH2-CH2--CH3
c.
CH3—CH2--O-CH-CH2.-CH2-CH3
\—ç D
r(
5
—
CH3
Draw condensed structures for the following ethers:
d. methoxycyclohexane
e. 3—methoxycyclopentene
f. 4—ethoxynonane
g. 2—isopropoxybutane
cc- C4-CR-
C C
C
zCR
C
2
cC c
Section 26.3
c
Aldehydes and Ketones
The next two organic functional groups we will study are those of the aldehydes and ketones.
Aldehydes and ketones contain a carbonyl group, which consists of an oxygen atom which is
double—bonded to a carbon atom. There are two kinds of carbonyl groups involved here. In aldehydes, at
least one hydrogen is attached to the carbonyl carbon, while in ketones, two carbon atoms are always
attached to the carbonyl carbon.
0
II
0
II
0
II
—C—
—C—H
—C—CC—
carbonyl group
aldehyde group
ketone group
I
26—6
I
©1997, A.J. Girondi
It is helpful to note that in an aldehyde the carbonyl carbon is always a terminal carbon, which means it
of the carbon chain. In ketones, the carbonyl carbon is never a terminal carbon.
always occurs at one
The nomenclature of aldehydes requires a few rule modifications:
Additional Rules for the Nomenclature of Aldehydes:
RULE 1: The longest continuous chain containing the aldehyde group is considered to be the parent
compound.
RULE 2: The carbonyl carbon is part of the parent chain and is always considered to be in the #1 position.
RULE 3: The suffix “al” is added to the name of the parent compound to indicate that the compound is an
aldehyde.
Note the examples of aldehydes shown below. You see that no number is needed to indicate the
position of the functional group since it is always at position #1.
I
CH3—CH2- C
propanal
H
CH3
H
o
I
I
CH3-CH--CH2--CH2- C =0
4—methylpentanal
CH3
0
CH2-CH3
I
II
H— C— CH—CH--CH2--CH-CH2--CH2--CH-CH2--CH3
5—ethyl—8--methyldecanal
The nomenclature of ketones also requires a few rule modifications.
Additional Rules for the Nomenclature of Ketones:
RULE 1: The longest continuous chain containing the ketone group is considered to be the parent
compound.
RULE 2: A number is included before the name of the parent compound to indicate the position of the
ketone group. The chain is always numbered so that the carbonyl carbon has the lowest
possible number.
RULE 3: The suffix “one” is added to the name of the parent compound to indicate that the compound is
a ketone.
For example:
0
II
CH— C— CH3
0
II
CH3— CH2— C— CH2
CH3
2—propanone
3—pentanone
26—7
CHa-CH-CH2-CH2--CH2-C
CH3
0
CH3
6—methyl—2—heptanone
©1997, A.J. Girondi
Why would it be impossible for a ketone to have a name like 3—methyl—1--hexanone? {3L
o
•4 cc
VQ (-“ilet
Problem 4. Name the molecules shown below.
a.
0
II
CH3CH2—C-CH3
b.
0
II
CH3— CH— CH2— C— H
an
.
1
CH3
c.
CH3
i
CH3—CH2-CH--CH—CH3
/
H
CH2-CH3
CH3
d.
CH3—CH-CH-CH2--C= 0
C)
CH3
CH3—CH2--CH2
e.
C0
I
(ftQA kQ q
O
CH3
I
CH2-CH2-CH-CH3
Section 26.4
-
Organic Acids
Organic acids are molecules that contain a carboxyl group (sometimes called a carboxylic acid
group). This functional group consists of a carbon which is doubled bonded to an oxygen atom, as was
the case with aldehydes and ketones. However, in an acid a hydroxy group (—OH) is also bonded to that
same carbon. Be careful not to onfuse organic acids with alcohols, aldehydes, or ketones. As was the
case with aldehydes, this functional group always occurs on a terminal carbon of the parent chain.
Therefore, a number is not used in the name to locate the carboxyJ group.
Additional Rules for the Nomenclature of Carboxylic Acids:
RULE 1: The longest continuous chain containing the carboxyl group is considered to be the parent
compound.
RULE 2: The carboxyl carbon is part of the parent chain and is always considered to be in the #1 position.
RULE 3: The suffix “oic” is added to the name of the parent compound, and the word “acid” is added to
the name.
26-8
©1997, A.J. Girondi
For example:
O
0
H_C\
CH3
CH3—C\
OH
0
CH3—CH-CH2-CH2—C\
OH
methanoic acid
OH
4—methylpentanoic acid
ethanoic acid
Acids also have common names. For example, ethanoic acid is also called acetic acid or “vinegar.” We will
work only with the IUPAC names.
As you attempt to name the carboxylic acids, note that the carboxyl group is written in shorthand as
—COOH in the condensed structural formulas.
Problem 5. Name the organic acids below.
a.
CH3-CH2--CH-CH2--CH2--COOH
CH2—CH3
b.
CH--CH2--CH2--CH2--CH2--COOH
C.
CH3-CH2--CH2
CLCiA
3x?
2-
CH3-CH-CH-CI-I--qOOH
d.
L
CH3
e.
ac X
-
CH3
f CH
\l
CH-CH2-COOH
CH3
CH2-CH2-CH2-CH
f.
LILL\
CH3-C-CH2--CH2-COOH
ccc
1
rcacc
CH2-CH2--CH2-CH3
Section 26.5
Esters
Esters are organic compounds which are very common in nature. For
example, fats and oils are esters. Esters are also responsible for many of the odors
and flavors of fruits. Oil of wintergreen and aspirin are esters. Esters can be
considered to be derivatives of carboxylic acids. The functional group of esters looks
similar to the carboxyl group of acids, except that the hydrogen atom on the hydroxy
group is replaced with an organic group such as an alkyl group. The letter “R” in the
structure at right represents some organic group (methyl, ethyl, etc.).
26—9
0
-C’
4’
©1997, A.J. Girondi
0
—C
0
-C—
-c
\
0—H
0—R
0—CH3
sample ester group
general ester group
carboxyl group
Esters are named by first naming the “R” group followed by the name of the acid portion. The suffix of the
acid derivative is then changed from “—Ic” to “—ate.” For example, in the leftmost structure below, the
In the
parent acid is ethanoic acid. The “R” group is methyl, so the name of the ester is methyl ethanoate.
center structure, the parent acid is butanoic, while the “R” group is ethyl, so the ester is named ethyl
butanoate. Notice that the names of esters consist of two words, while the names of most of the previous
types of compounds you have studied consisted of only one word.
CH3-C
4,
0
CH3-CH2-CH2-C
‘Q-CH3
4,
0
4,
H-C
Q-CH2-CH3
0-CH2-CH3
ethyl methanoate
(artificial rum flavor)
ethyl butanoate
(pineapples)
methyl ethanoate
0
Artificial flavors of strawberry, apple, raspberry, cherry, etc., are made from esters.
Additional Rules for the Nomenclature of Esters:
RULE 1: Determine the name of the “R” group.
RULE 2: Place the name of the “R” group in front of the name of the parent acid, forming two words.
RULE 3: Determine the name of the parent acid, and change its suffix from “—Ic” to “—ate.” Drop the word
“acid.”
Problem 6. Namethe esters below.
0
a.
b.
CH3—CH2-CH2—C
4’
0
CH3-CH2-CH2-CH2-C
Q—CH
Q-CH2-CH2-CH3
‘
c.
CH3—CH2—C
4’
0
\_
d.
CH3-C
4,
0
‘0-CH-CH3
CH2—CH2—CH2—CH3
CH3
4\
)S)(\((
26—10
©1997, A.J. Girondi
__________
0
0
f.
e. CH3-CH2-CH2—CH2--C
H-C
0— CH2—CH2—CH2—CH2—CH3
‘0—CH2-CH2-CH3
\
\p\
Section 26.6
Amines
Amines are organic compounds which are related to ammonia (NH3). All amines have the element
nitrogen in them. There are three basic kinds of amines:
1. In prima,y amines one hydrogen atom in ammonia has been replaced by an alkyl group.
2. In secondary amines two hydrogen atoms in ammonia have been replaced by two alkyl groups.
3. In tertiaiyamines all three hydrogen atoms in ammonia have been replaced by three alkyl
groups. Examine the examples below:
H
I
CH3—N—H
H
I
CH3— CH2—N—CH2—CH3
CH3—CH—CH3
I
CH3—N—CH2CH3
A Primary Amine
A Secondary Amine
A Tertiary Amine
According to the IUPAC system, primary amines are named by treating the —NH2 (amino) group in
the molecule as a substituent group on the longest (parent) chain of carbon atoms. For example, the
primary amine shown above is called aminomethane. Two more examples are shown below.
CH3-CH2—CH-CH2—CH2—CH3
I
H—N—H
NH2
CH3
I
I
CH3-CH—CH2—CH-CH2—CH2—CH3
3—aminohexane
(a primary amine)
4—amino—2—methylheptane
(a primary amine)
Secondary and tertiary amines are named according to a “common” naming system. Primary
amines can have either IUPAC or common names. Amines are the only organic compounds for which we
will learn common names. In the common system, amines are named by adding the names of the alkyl
group(s) attached to the nitrogen atom to the word “amine.” In the past, the alkyl groups were named in
order of size (smallest first) instead of in alphabetical order is normally done in the IUPAC system.
However, today we follow the IUPAC rules and name the alkyl groups in alphabetical order. For example,
the name of the secondary amine shown above is diethylamine. The name of the tertiary amine above is
ethylisopropylmethylamine. Study the examples below. Note that the primary amine can have two names.
26—11
©1997, A.J. Girondi
CH3
CH2— CH2
I
CH3—N—CH3
CH2— CH2
CH3
I
I
H—N—CH3
H—N—H
trimethylamine
a tertiary amine
CH2— CH2— CH3
methylpropylamine
pentylamine (common)
a secondary amine
1—aminopentane (IUPAC)
a pnmaiy amine
Additional Rules for the Nomenclature of Amines:
RULE 1: In primary amines only, the IUPAC system treats the NH2 (amino) group as a substituent group
on the parent chain.
RULE 2: When using the common naming system, the names of the alkyl groups which are attached to
the nitrogen atom are listed in alphabetical order and are attached to the suffix “amine” to
form one word. Greek prefixes are used if specific alkyl groups occur more than once in a
molecule. Name the amines below. Where two lines are present, give two names.
Problem 7. Name the amines below. Where two lines are present, give two names.
a.
CH3
CH3— N— CH2— CH3
b.
U
H
c
CH3— N— CH2— CH3
L)
c.
2(L(1\Z(E)9 -mdpwLQ
CH3—CH2-CH2—CH—CH2-CH—CH3
NH2
CH3
d.
0
CH3— CH2— CH2— CH2— CH2
Q
H— N—CH3
CH2— CH3
e.
‘
CH3— CH2— N— CH2— CH3
CH2— CH3
f.
CH3—CH—CH2—CH2—CH2— CH2— CH2— NH2
NH2
g.
2—c
01 ?sc
CH3—CH— CH3
26—12
)_
N
j(j
Cji1tRL (Cc’.vr©1997, AJ. Giroridi
NH2
h.
oCdc 2
Section 26.7
Amides
You are already familiar with the carboxyl group which is the functional group of a carboxylic acid. If
you replace the hydroxy group (—OH) in the carboxyl group with an amino group (—NH2), you get the
functional group of a class of organic compounds known as primary amides.
-c’Q
SO—H
amide group
carboxyl group
There are three classes of amides just as there were for amines, but we will consider only primaly
amides, and we will name them according to the IUPAC system. Amides are considered to be derivatives
of carboxyllc acids, which means they are formed from acids. Thus, the amides are named as derivatives of
acids. To name an amide, simply identify the name of the organic acid from which the amide was derived,
and change the “—oic” suffix in the acid’s name to “—amide.” The examples of amides shown below were
derived from ethanoic, propanoic, and butanoic acids.
CH3
C\
CH
—
3
CH3CHCH2C\
CH3CH2C\
ethanamide
NH2
2
NH
NH2
3—methylbutanamide
propanamide
Additional Rules for the Nomenclature of Amides:
RULE 1:
Identify the carboxylic acid from which the amide was derived and change the suffix of the acid
name from “—oic” to “—amide,” and drop the word acid.
RULE 2:
Add the names of any alkyl groups to the name of the parent compound, forming one word.
Problem 8. Name the amides shown below.
shorthand as CONH2.
Note that the amide functional group is written in
b. CH3-CH2--CH2--CH2-CONH2
a. HCONH2
Atca cLcr’
26—13
©1997, A.J. Girondi
CH3
CH2CH3
C.
d.
CH3—c-CH.2-CONH2
-!
HN2
2
H2-CH--CH2
D
CH3
‘33-d.
L\X4.
CH3
1
CH2-CH3
e.
-
[5
qHH2-cH-cH2-cH-çc NH2
CH3
CH3_CH_CH2?_CH2CONH2
CH3
CH3
mkhncm&
Section 26.8
Halogenated Hydrocarbons
The last group of compounds we are going to discuss includes some that are of great importance
and interest today. Included are the chlorofluorocarbons that are used in refrigeration and air conditioning
systems and which are thought to be involved in the depletion of ozone in the upper atmosphere.
This class of organic compounds is known as the halogenated hydrocarbons. In addition to their
use in refrigerants they are used as solvents, aerosol sprays, antiseptics, dry cleaning fluids, insecticides,
herbicides, and anesthetics. Most of these compounds are synthetic (human— made).
In these compounds, the functional group is a single atom of a halogen such as fluorine, chlorine,
bromine, or iodine. In the IUPAC system, the halogen atoms are considered to be substituents on the
parent chain. The “—me” suffix of the halogen’s name is dropped and the letter “o” is added before being
added to the name of the parent compound. For example, fluorine becomes “fluoro,” chlorine becomes
“chioro”, bromine becomes “bromo,” and iodine becomes “iodo.” Note the examples below.
H-C-I
HH
II
H-C-C-Cl
HFHHIHHH
lIlIllIl
H-C-C-C-C-C-C-C-C-H
I
II
HHH
III
H-C-C-C-Br
III
1111
H
HH
HHH
HHHFHHHH
iodomethane
chlororiethane
CH—I
CH3—CH2-Cl
H
1—bromopropane
CH3-CH2-CH2-Br
1111
2,4—difluoro—5—iodooctane
CH3-CHF-CH2-CHF-CHI-CH2-CH2-CH3
Numbers are not used to indicate the position of a single halogen atom substituent unless the parent
carbon chain is longer than 2 atoms; however, if more than one halogen atom substituent is present, then
numbers are needed on a two—carbon chain, too! Study the following examples.
HCI
II
H-C-C-Cl
I I
HH
I ,I—dichloroethane
HH
II
Cl-C-C-Cl
II
HH
I ,2—dichloroethane
26—14
Br
H-C-H
F
bromofluoromethane
©1 997, A.J. Girondi
Additional Rules for the Nomenclature of Halogenated Hydrocarbons:
RULE 1:
Drop the “—me” suffix from the name of the halogen atom(s) and add a suffix consisting of the
letter “0”.
RULE 2:
Add the altered name(s) of the halogen atom(s) to that of the parent compound.
Problem 9. Name the halogenated compounds below.
Cl
I
CH3—CH2--CH--CH—CH3
5
a.
-zcco xoa
2
3
.
1
Cl
H
b.
—.
F—C—F
H
I
c.
Lj
I
2.
-
CH3—CH-CH—CH-CH2-CH3
Br
F
d.
Br
I •z
CH3—CH—CH=CH2
e.
CH2—CH2—CH2—Br
3. D
Lt
CH2-CH2
;
f.
bcoir- 2V loco 3-r
do h.c&xaftL
0
-
CH2
-
‘
H
CH3
Cl-C-Cl
(4:
,
-
F
Problem ‘10. Write condensed structural formulas (such as those shown above) for the following.
a.
tetrafluoromethane
F
b.
I ,1,I—trichloroethane
3
c--c
C’
26—15
©1997, A.J. Girondi
C.
chlorocyclopentane
d.
1 ,3—difluoro—2—iodocyclohexane
e.
3,4—dibromo—6—methyl--1—heptyne
/\
f.
3—chiorocyclopentene
g.
2,3—dichlorocyclobutene
Section 26.9
F
.
C C-c Ck-C-c -c
3
3
c
A Review of Organic Nomenclature
The remainder of this chapter consists of a review of nomenclature of the various classes of
organic compounds which you have studied.
Problem 11. Some of the names of the six compounds listed below are incorrect. If the name is
correct, respond with “O.K.” If the name is incorrect, provide the correct name.
C’
-c—c
a. 3—chioropentane
Cc
b. I ,I—dimethyl—1—propanol
(C
c
s.
2
c. 2,2,3—trimethyl—4--bromoheptane
6
d. 4—methyl—4—hexanol
)
‘
CE-C
C
(l
C
C’c
f. I—ethyl—2—ethanol
c-c
t)
3.
e. 2,2—dimethyl—3—chloro—3—butanol
-(-L
fl
\—
26—16
.
S
©1997, A.J. Girondi
Problem 12. Draw condensed structural formulas for the compounds named below.
a. I ,3,5—tribromocyclohexane
b. 2,3—dichiorobutane
c. 2—ethyl--3--methyl—I —pentanol
d. 1—ethoxypropane
o
e. 2—iodo—3—isopropylcyclohexanol
f. 3,3—dimethylbutanal
Ck4
C4_
3
Cc
g. 2—methoxy—3—heptanone
a
h. 3—pentanone
C
1
CC
3
C
(3
i. 3,4—diethyihexanal
j. 2,4—difluorohexanoic acid
F’
-C- -c”
I
,C
C\3
k. 2—hydroxybutanoic acid
I. ethyl ethanoate
m. n—propyl octanoate
n. 4—bromo—3—chloroheptane
C4- c -c
C.CC-C 2
26—17
-
L
©1997, A.J. Girondi
o. ethylmethylamine
p. isopropyldimethylamine
3
-CC.•
c
cM
r. 3—methylbutanamide
q. propanamide
0
C- c-c’.
-c”
1
C\-c
3
c
t. 2,3,4—triiodopentanoic acid
s. 4—chloro—2—pentanone
.0
C-c -c
Problem 13. Give another name for each of the following:
a. ethylamine
b. isopropylamine
.j (..._
2 Q
\ ‘(‘. I ..
ñC)
(‘)( .
(.
3
C Ck-C\
3
Section 26.11 Learning Outcomes
Before leaving this chapter, read through the learning outcomes listed below. Place a check
before each outcome when you feel you have mastered it. When you have completed this task, arrange
to take any quizzes or exams on this chapter.
1. Given their names or condensed structural formulas, distinguish between alcohols, ethers,
aldehydes, ketones, organic acids, esters, amines, amides, and halogenated compounds.
2. Given their names, draw condensed structural formulas for the classes of compounds given in
outcome 1 above.
3. Given their condensed structural formulas, give the IUPAC names of molecules belonging to
the classes of compounds listed in outcome I above.
4. Given their condensed structural formulas, give the common names of secondary and tertiary
amines.
26—18
©1997, A.J. Girondi
NAME__
____
PER
DATEDUE__________
ACTIVE LEARNING IN CHEMISTRY EDUCATION
CHAPTER 27
INTRODUCTION
TO ORGANIC
COMPOUNDS
(Part 3)
27-1
@1997k A.J. Giroridi
SECTiON 27.1
Aromatic Compounds
An important class of carbon compounds exists which was not discussed in Chapters 25 or 26.
This class of compounds was discovered during the early years of the study of organic chemistry.
Because these compounds had sweet smelling odors they came to be known as the aromatics, although
some of them have no such odor.
These compounds are still called aromatics, although the name no longer applies to any odor.
Instead, compounds are now classified as aromatic if they contain a particular structure.
The alkanes, alkenes, and alkynes discussed in Chapter 25 are categorized according to whether
they contained single, double, or triple bonds. Alcohols, ethers, aldehydes and the other classes of
compounds discussed in Chapter 26 are categorized according to the presence of a specific functional
group. The parent compound found in all aromatic molecules is benzene.
Benzene was discovered in 1825 by Michael Faraday who was at the time analyzing “illuminating
gas.” Benzene, itself, is the simplest member of the aromatic family. About ten years after its discovery, its
formula was determined to be C&-16. However, the problem of determining the structure of benzene
persisted for several decades. The molecule contains only one hydrogen atom for each carbon atom.
Many different structures were proposed, some of which are shown below.
I-I
H
I
I
H
H
Slructure I
H-C=C-CE C-C=C-H
I
I
H
H
II
H-CE C—CE C-C-C-H
II
HH
Structure 2
H
I
H—C-CE C—CE C—C-H
I
I
1-I
H
Structure 4
HH
I
I
N-CE C-C=C-C=C—H
H
H
H
I
I
H
Structure 3
HH
I
II
H-CE C—C=C= C—C—H
I
H
Structure 5
H
H
I
I
H—C-CE C-C=C=C-H
I
I
H
H
Structure 6
Benzene was found to be a rather stable molecule. Eventually, chemical testing revealed that
none of these six “straight-chained” structures could explain the properties of benzene. Finally, in 1865,
the chemIcal structure of benzene was predIcted b the German chemist, Kekule. As the story goes,
Kekule fell asleep one night sitting in front of a fire and had a dream about chains of carbon atoms
behaving like twisting snakes. Suddenly, one of the snakes bit its own tail forming a ring, giving Kekule
the inspiration to spend the rest of the night devising a ring structure for benzene. As a result, Kekule is
remembered by his famous quote, “Let us learn to dream gentlemen, and then perhaps we shall learn the
truth.”
H
I
The structure which Kekule proposed was a ring consisting of six
carbon atoms joined by alternating single and double bonds. Each H—
H
carbon atom was also bonded to one hydrogen atom. The stability of the
molecule needed to be explained, as did the fact that when it reacts in a H—
H
vne-to-one mole ratio with bromine, benzene forms only one di-substituted
product (containing two bromine atoms), when two different products
H
would be predicted as shown below.
Benzene
‘b,
27-3
I
@1997, A.J. Girondi
H
H
H
Br
H
Br
H
OR
Br
Br
H
H
This evidence suggested that all of the bonds in benzene were equivalent. To solve this problems
Kekule suggested that the double bonds and single bonds in the ring shifted back and forth, and this
shifting made all of the bonds sites equivalent:
H
H
H
However, benzene does not react like the alkenes which really do have double bonds. Today, we use the
‘theory of resonance to describe the structure of benzene. This theory suggests that. berizene does not
contain single bonds or double bond& Instead, the bonds between the carbon atoms are all Identical.
They are called resonance hybrids meaning that they have properties which are between single and
double bonds, such as the length of the bonds. The length of carbon to carbon single bonds and carbon
peptiyiy. The)ngjti f tFe carbon
o oaron doubJe bonds are 154 Angstrorns and 134 Mgstroma,
tecarbon resonance hybrid bonds In the benzene ring Is ‘1.39 Angstroms. According to this theory óach
carbon on the molecule would be identical. Therefore, only one product would be expected when
benzene reacts with bromine. You may still see benzene represented with alternating single and double
bonds, but it is understood that they are actuaHy identical resonance hybrids. Some chemists use other
symbols to represent benzene, including the structure shown below with the circle inside the ring. (The
hydrogen atoms present on the ring are usually not written. They are assumed to be there, unless they
are replaced by an atom of another element.)
.
QOR©
Benzene
Benzene
Section 25.2
Naming Aromatic Compounds
Aromatic compounds.have both common names and IUPAC names. In Chapters 25 and 26 we
did not include common names. However, because they are still widely used with aromatic compounds,
we will include them in this chapter. When a hydrogen atom on the benzene ring is replaced by some
other substituent;” the compound can be named as a derivative of benzerie. In other words, benzene is
considered to be the parent compound. Common substituents include:
brorno
chloro
fluoro
lode
nitro
amino
hydroxy
methyl
ethyl
—Br
—CI
—F
—I
274
—N02
—NH2
—OH
—0H3
—C2F-15
©1997, A.J. Girondi
Naming the compounds in this way, gives the LUPAC names:
CHa
CH2- CH3
methylbenzene
chlorobenzene
ethylbenz-ene
o
bromobenzene
CH—CH -CH
isopropylbenzene
nitrobenzene
arninobenzene
Note how the flJPAC names always end with ‘benzene.” When the ring contains only one substituent, It
is not necessary to include number in the name, because allQf the carbons are equivalent.
When the ring contains more than one substituent, the names. become more complex. When the
ring .has two substituents, the prefixes ortho, meta, and pars are used to describe the positions of the
substituents. Ortho refers to adjacent positions,, while meta describes two positions separated by one
carbon atom. Para positions are located across from each other on the ring. The prefixes can be
abbreviated as 0-, m-, and p. as in the examples below. The substituents appear In the names In
alphabetical order:
CH3
m-hydroxymethylbenzene
o-bromochlorobenzene
N02
4
.
1
h
0
.
loronltrobei
-
Prefixes are used when more than one identical substftuent occurs on the ring. Note the use of the prefix
“dl” in the name of the structure below.
Prefixes are used when more than one
identical substituent occurs on the ring. Note
the use of the prefix “di” in the name of the
structure shown at right.
Cl.4
m-chiorohydroxybenzene
—
The structure at left has only
two
substituents. Note that in the IIJPAC name
the substituents are in alphabetical order
(chloro before hydroxy).
27-5
p-dlchlorobenzene
(paradichlorobenzene)
©1997, AJ, Girondi
Problem 1.
provided.
I
Give IUPAC names for the structures shown below. Write your answers in the space
b.
a.
Cl
.
bC! 0
‘.
C.
,.‘
d.cy
d.ZJL____
Structural isomers are compounds that have the same formula but different structures. Three
structural isomers of dibromobenzene are possible. They are shown below with their ItJPAC names.
Br
Br
Br
1Br
o-dibromobenzene
(orthodlbromobenzene)
m-dibromobenzene
4rnetadlbromobenzene)
When the ring has three or more substituents, they are
located by numbering the ring. The carbons in the ring
are numbered so as to give the substituerits the lowest
possible numbers. (as was the case with the cyclic
compounds you studied in previously). The compound
Shown at rigN is called I ,2,4—trichlorobenzene.
Prefixes like di, tn, etc., are not considered when
putting names of substituents in alphabetical order.
Consider the name of the structure at right. It is called
i-tluoro-2,3-dimethylbenzene. Note that “fluoro” comes
before “methyl.” The prefix “di” is ignored.
Note that the structure at right is 1-bromo-2-chloro-4hydroxybenzene. It is nj called I-hydroxy-3-chloro-4bromobenzerie,because numbering the ring that way
would give put higher numbers in the name.
27-6
p-dibromobenzene
(paradibromobenzene)
Cl.
CH3
H3
CJ1OH
@1997, A.J. Girondi
When numbering a ring in either of two ways gives
the same set of numbers, then give the lowest number to
the substituent which appears first in the name (see
structure at riht).
It is called 1-bromo-2-chloro-3iodobenzene,
It is
called 1-iodo-2-chloro-3bromobenzene.
I
Problem 2 Name the compounds shown below using the IUPAC system:
CH
CH2—CH3
QeflZfM
a.
b.
Br
OH
e.
Br
f.
N02
N02
CI
d.
e.
a
co(rp-
Problem 3. Draw structures which satisfy each of the following IUPAC names:
a. I ,2-dichloro-4-methylbenzene
b. I ,3,5-trimethylbenzene
CJ4
/
\0
C’tk
C. o-diiodobenzene
d. m-hydroxyiodobenzene
/c
27-7
@1997, A.J. Girondl
a. p-diethylbenzene
S
f. I ,3-dibromo-5-chlorobenzerie
3
Ck
/
Problem 4. The following IUPAC names are incorrect. Draw the structure that satisfies the name, and
then write the correct name:
a. 2,3-dichlorobenzene
b. I -chloro-5,6-dibromobenzene
ç
c. 2-hydroxy-4,6-difluorobenzene
d. I -chloro-2-amlno-5-chlorobenzene
C’
0
•
Section 27.3
/
NV
—
The Common Names of Aromatic (Benzene) Compounds
Remember, in the IUPAC system compounds are named as derivatives of benzene and,
therefore, IUPAC names end with ‘benzene.” Note the common names of the compounds shown below.
The IUPAC names are also given.
Common Name:
IUPAC Name:
CH3
OH
NH2
toluene
methylbenzene
phenol
hydroxybenzene
aniline
aminobenzene
27-8
©1997 A.J. Girondi
We will now consider the common names of some benzene compounds that have two
substituents on them. Note, however, that they are named as derivatives of toluene, phenol, or aniline,
rather than benzene.
CH3
OH
NH2
Br
o-chlorotoluene
NH2
p-aminoanhline
m-bromophenol
Problem 5. Give the IUPAC names of the three structures shown above.
a.
—
-
——
bL)
When the two substituents on the benzene ring are methyl groups, the compounds are known as
xylenes in the common naming system. There are three forms of xylene:
CH3
CH
CH3
CH3
CH3
o-xylene
CH3
p-xylene
m-xylene
Since xylenes are a special case, they should
be named as derivatives of toluene. For example,
o-xylene should
be named o-methyltoluene. The common naming system, like the IUPAC system,
makes use of the numbering of the ring for structures with three or more substituents. Note the common
names of the structures below:
CH3
OH
NH2
NH2
Br
Common Names:
2-amino-4-iodotoluene
27-9
2,5-dichlorophenol
m-bromoanhline
@1997, A.J. Girondi
_____________
Problem 6. Give the IUPAC names of the threestructures above.
icflzftQ
b.i_jQZ2Zb
TNT is an abbreviation that comes from the common
name for an explosive. Its structure is shown at right.
Its common name is 2
4,6-trinitrotoluene. What is its
1
ItJPAC name?
‘ )Ztfl
N02
ft.Q..
examine the structure at right. Its common name is 2,3dibromotoluene. Note that “methyl” is not part of its common
name because the methyl group Is part of the toluene structure.
Since it is part of the parent compound in the common name
(toluene), the methyl group is numbered as being on the number
I carbon in the ring. That’s why we do not call it 1,2dibromotoluene.
Problem 7.
N02
Br
Br
Name the following compounds twice, using the common and IUPAC systems.
OH
Common:
b.
NH2
Common:
lUPACJ)L(L
CH2—CH3
C.
Common:
0H3
27-10
@1997, A.J. Girondi
CH3
d
Common:
ClJ.
JUPAC
Br
a.
Common:
‘
IUPAC:
f.
Common:
SQ
ZCfl(’-
NH2
Cl
Problem 8. The following common names are incorrect. Draw the structure that satisfies the name
given, and then write the öorrect common name:
a. 4,5-dichiorophenol
3
c&
b. 3-bromotoluene
c. 4,5-dibrómoaniline
3R
/
\Q)
c ‘occ çn\?ftQ
d. 4-methyltoluene
\S
Section 27.4
Condensed Ring Structures
There are some common aromatic structures which are not composed of benzene rings with
substituents on them. These compounds are known as condensed ring structures. They look somewhat
like a number of benzene rings which have been bonded together. Three examples of condensed ring
structures which are extracted from coal tar include:
27-11
@1997, A.J Girondi
naphthalene
anthracene
phenanthrene
Like p-dichlorobenzene, naphthalene is often used to make moth balls. Anthracene is used in
the manufacture of dyes, and steroids are compounds which are based on the structure of phenanthrene.
Since aromatic chemistry developed in a rather haphazard way for many years, many of these compounds
were given common names (such as those above) which are still used today. These compounds do not
actually exist in coal tar; instead, they are formed when coal tar Is heated (distilled). It is believed that some
condensed ring structures are formed whenever organic molecules are heated to a high temperature.
This includes the burning of tobacco in cigarettes. The bad news is that many of these compounds have
been shown to produce cancer. Workers at plants where coal tar is distilled have had higher than normal
rates of skin cancer. Needless to say, condensed ring structures are also suspect in the development of
lung cancer.
Section 27.5
Learning Outcomes
This is the end of your study of organic nomenclature in the ALICE program. You should know
that organic chemistry is a very large field of study. New organic compounds and products are being made
every year. Students of organic chemistry not only learn about the classification and nomenclature of
compounds. This is actually only a very small part of what they study. Some of the most Important
research being done in science today, involves the study of reactions that organic compounds undergo.
This field is very important in agriculture, medicine, manufacturing, and many other fields of human
endeavor. Be sure that you have mastered each of the learning outcomes below.
____1. Distinguish between organic structures which belong to the aromatic class of compounds and
those which do not.
2. Draw the structure of simple aromatic molecules given their iUPAC names.
____3. Write the IUPAC names of simple aromatic molecules given their structures.
___4. Draw the structures of simple aromatic molecules given their IUPAC names.
____5. Draw the structures of simple aromatic molecules given their common names.
___6. Recognize the structure of condensed ring structures.
27-12
@1997, A.J. Girondi