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ORGANIC CHEMISTRY
-Organic molecules
contain only C, H, O, N
and sometimes S and P
-56 204 570 organic
substances have been
recorded
What allows for the diversity of organic compounds?
-Carbon can make 4 bonds
-The 4 bonds can be a combination of single, double,
and triple bonds
methane, CH4
methanal, CH2O
ethanenitrile, CH3CN
Naming Hydrocarbons
What’s in a Name
Assembled from components that describe various
features of the molecule.
root
suffix
Functional
group
Number of
carbons in the
longest chain
Ex: methane
Ex: butanol
Root Name = Longest Chain
• The longest continuous chain of carbons containing
the principal functional group defines the root name.
• Other groups attached to this chain are called
substituents.
Longest Carbon Chain Name
methethpropbutpenthexheptoctnondecundecdodec-
= 1 carbon
=2
=3
=4
=5
=6
=7
=8
=9
= 10
= 11
= 12
Just FYI…
13
trideca-
30
triaconta-
500
pentacta- 7000
heptalia-
14
tetradeca-
40
tetraconta-
600
hexacta
octalia-
15
pentadeca
50
pentaconta-
700
heptacta- 9000
16
hexadeca-
60
hexaconta-
800
octacta-
17
heptadeca
70
heptaconta-
900
nonacta-
18
octadeca-
80
octaconta-
1000 kilia-
19
nonadeca-
90
nonaconta-
2000 dilia-
20
icosa-
100 hecta-
3000 trilia-
21
heneicosa
200 dicta-
4000 tetralia-
22
docosa
300 tricta-
5000 pentalia-
23
tricosa
400 tetracta-
6000 hexalia-
8000
nonalia-
Principal Functional Group =
Suffix
• The principal functional group is used to define the
class the compound belongs to e.g. an alkene, alcohol,
etc.
• Determines the suffix of molecule’s name
• Refer to ‘Families of Organic Compounds’ handout
Lesson 3 Success Criteria
• Student will be able to:
– Recognize the molecular formula of alkanes
– Draw different structures of alkanes,
cycloalkanes & haloalkanes.
– Name alkanes, cycloalkanes & haloalkanes
using IUPAC rules
– Determine if a compound is a structural
isomer
Basic Naming Rules
The IUPAC systematic name of an organic compound can
be constructed based on a series of steps and rules:
1. Identification of the principal functional group and
substituents
2. Identification of the longest continuous chain
containing the principal functional group.
3. Assign locants (i.e. numbers) to the principal
functional group and substituents.
First Set of Functional
Groups:
HYDROCARBONS
Hydrocarbons:
When an organic molecule is composed only of hydrogen and
carbon, it is called a hydrocarbon:
Alkanes: Hydrocarbons with single bonds
Alkenes: Hydrocarbons with double bond(s)
Alkynes: Hydrocarbons with triple bond(s)
ALKANES
-Characterized by C-C single bonds
-Also known as saturated hydrocarbons
-empirical formula = CnH2n+2
 CnH2n+2, n=8
= C8H18
ALKANES
Properties:
-Hydrophobic (does not mix with water and other polar
substances)
-Generally low boiling points (due to weak London Dispersion
Forces)
- Longer alkane molecules have higher boiling points
ALKANES
Some IUPAC* names of alkanes:
ethane
propane
butane
All alkanes have the suffix “ane”
*International Union of Pure and Applied Chemistry
ALKANES
IUPAC naming system:
Molecular
formula
Expanded Molecular Formula
Name
CH4
CH4
methane
C2 H6
CH3CH3
ethane
C3 H8
CH3CH2CH3
propane
C4H10
CH3CH2CH2CH3
butane
C5H12
CH3CH2CH2CH2CH3
pentane
C6H14
CH3CH2CH2CH2CH2CH3
hexane
C7H16
CH3CH2CH2CH2CH2CH2CH3
heptane
C8H18
CH3CH2CH2CH2CH2CH2CH2CH3
octane
C9H20
CH3CH2CH2CH2CH2CH2CH2CH2CH3
nonane
C10H22
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
decane
ALKANES
IUPAC naming system:
Name the following alkanes:
1
2
3
4
hexane
5
6
1
2
3
4 5
6
nonane
7 8
9
Substituents: Branches in
Chains
Not all alkanes are straight chains. Some alkanes
have alkyl side groups (alkyl substituents) attached.
-CH3
methyl
-C2H5
ethyl
-C3H7
propyl
-C4H9
butyl
-C5H11
pentyl
-C6H13
hexyl
-C7H15
heptyl
-C8H17
octyl
Ex:
methyl group
name: 2-methylbutane
IUPAC naming system:
For alkanes with side groups…
Substituent(s)
Branches
prefix
suffix
family
Number of
carbons in the
longest chain
Ex: 2-methylbutane
Assigning Locants (i.e.
numbering)
• The numbers that define the positions of the principal
functional group and substituents are called locants.
• Compounds are numbered from one end of the longest
continuous chain.
• The locants are assigned such that the principal
functional group gets the lowest possible locant
IUPAC naming system:
Name the following branched alkanes
1
2
3
4
5
2-methylpentane
1
2
3
4
5
3-methylpentane
When there is ambiguity, the substituent
must be numbered according to the carbon
atom that it is attached to
(aim to get the lowest possible number)
First Point of Difference:
Which name is incorrect?
1
2
3
4
5
2-methylpentane
5
4
3
2
1
4-methylpentane
Aim for the lowest possible number when
counting.
ALKANES
For alkanes with multiple branches of the same kind
attached to the main chain….
•
•
•
•
give each branch a number.
list the numbers in ascending order.
give the branch name a multiplying prefix (i.e.
di, tri, tetra, etc.) to indicate the number of
identical branches.
put commas between numbers, and hyphens
between numbers and letters.
No space!
Ex: 4,6-dimethylheptane
ALKANES
IUPAC naming system:
Name the following branched alkane
4
1. Find the longest
continuous chain
of C atoms
(parent chain)
2. Identify any
substitutents
1
5
CH3 - CH - CH3
|
2
3
CH3 - CH - CH2
|
CH3
No space!
2,4 -dimethylpentane
ALKANES
IUPAC naming system:
For alkanes with multiple, but different kinds of
branched groups…
• name the branched groups in alphabetical
order.
• give the branch name a number to indicate
which carbon in the main chain it is bonded
with.
• put commas between numbers, and hyphens
between numbers and letters.
Ex: 4-ethyl-6-methylheptane
CH3
|
7
5
The order of
substituents in the
name is based on
alphabetical order
CH2 - CH2
6
|
3
4
CH2 - CH - CH2 - CH3
|
2
1
CH - CH3
|
CH3
3-ethyl-2-methylheptane
No space!
Numbering (con’t)
• If numbering a functional group results in a "tie" then the
first point of difference rule. The first time a difference
in numbering occurs, then the method that gives the
lower number at this first difference is used.
• In the event that there is no first point of difference then
alphabetisation is used.
ALKANES
IUPAC naming system:
Name the following branched alkane
3
The order of
substituents in the
name is based on
alphabetical order
4
5
6
2
7
1
8
9
4,5,5-triethyl -3,6,6-trimethylnonane
ALKANES
Drawing alkanes:
3 types of diagrams—all showing the same molecule
Structural diagram
Condensed diagram
Line diagram
CH3CH2CH2CH2CH2CH3
ALKANES
Drawing alkanes:
Line diagrams:
2
1
4
3
Every end or point on a line diagram
represents a carbon atom. Hydrogen
atoms are not shown.
6
5
ALKANES
Drawing alkanes:
Draw the following alkanes using line diagrams
2-methylbutane
2
1
3-ethyl-3,4-dimethylheptane
3
4
2
4
1
3
6
5
7
Nomenclature of Alkanes
Write the structure of 3-ethyl-2-methylpentane.
No First Point of Difference
• In the event that there is no first point of difference then
alphabetisation is used to determine numbering.
• Name this alkane:
1
8
2
7
3-ethyl-6-methyloctane
4
3
6
5
5
4
6
3
7
2
8
NOT
1 6-ethyl-3-methyloctane
• Two branches occur at C-3 and C-6, regardless of how the parent
chain is numbered
1
8
2
7
4
3
6
5
5
4
6
3
7
2
8
1
This time, there is a first point of difference at C-4
6-ethyl-3,4-dimethyloctane
Condensed Diagrams
• Bonds are (usually) not drawn. Only atoms
are drawn
• Entire molecule is written in one line (even
branches)
• Repeated fragments are simplified with
brackets
• Branches are also indicated with brackets.
Structural diagram
Condensed diagram
CH3CH2CH2CH2CH2CH3
CH3(CH2)4CH3
Condensed diagram
7
5 CH
6
2-
CH3
|
CH2
|
4
BE CAREFUL! A bracket to
indicate a branch can be easily
confused with a repeated
fragment. Typically brackets
such as (CH3) indicate a
branch, while brackets such as
(CH2) indicate a repeated
fragment that’s part of a main
chain
CH2 - CH - CH2 - CH3
3
2
|
CH - CH3
|
1 CH3
1
2
3
4
5
6
7
CH3CH(CH3)CH(CH2CH3)CH2CH2CH2CH3
CH3CH(CH3)CH(CH2CH3)(CH2)3CH3
CH3CH2CH(CH3)CH(CH3)CH2CH3
CH3CH2CH2CH=CHCH3
CH3CH2CH2CHCHCH3
It is common practice to
draw the multiple bond in
the condensed formula, but
the bond can be omitted
when its placement will be
obvious
CH3CH2CH(OH)CH2CH3
OH
O
(CH3O)2CH(CH2)4Br
Br
O
CYCLOALKANES
-Ring-like structures of alkanes
-empirical formula = CnH2n
 CnH2n, n=6
= C6H12
CYCLOALKANES
IUPAC naming system:
Name the following alkanes:
cyclobutane
cyclooctane
cyclopentane
The prefix “cyclo” is added to the alkane name
IUPAC naming system:
Name the following alkanes:
CH3CH2CH2
methylcyclohexane
CH
CH2
CH2
CH2
propylcyclobutane
Numbering the lcoation is not required, since the number is implied
3
3
1
1
3
1
1,3-dimethylcyclohexane
1
3
1-ethyl-3-methylcyclohexane
1,3-dimethylcyclohexane
If there are several substituents, the numbering of ring carbons then continues
in a direction (clockwise or counter-clockwise) that affords the second
substituent the lower possible location number
If two different substituents are present on the ring, they are listed in
alphabetical order, and the first cited substituent is assigned to carbon #1.
2
3
1
4
6
5
The disubstituted carbon becomes #1 because the total locator
numbers are thereby kept to a minimum. The methyl substituent is
then located on carbon #2 (clockwise numbering), and the ethyl
group is located on #4
4-ethyl-1,1,2-trimethylcyclohexane
CYCLOALKANES
IUPAC naming system:
Draw the following alkanes using line structures:
1,1-dipropylcyclopropane
1-ethyl-1,2,5-trimethylcyclopentane
HALOALKANES
HALOALKANES
-Alkanes with halogen atoms
-Also known as alkyl halides
HALOALKANES
IUPAC naming system:
Halogen groups:
-F
-Cl
-Br
-I
fluoro
chloro
bromo
iodo
Just like alkyl substituents, the halogens are placed at the
beginning of the name, and are ordered alphabetically.
HALOALKANES
IUPAC naming system:
Name the following haloalkanes:
1,2-dibromo-1-chlorobutane
2-bromo-2-methylpropane
2-bromo-2-chloro-1,1,1-trifluoroethane
STRUCTURAL ISOMERS
STRUCTURAL ISOMERS
Compounds with the same molecular formula
but with different bonding arrangements are
structural isomers.
Butane isomers
Pentane isomers
STRUCTURAL ISOMERS
Ex: Structural isomers of hexane + boiling points
Changing the structure affects the boiling point
This structure can easily stack and form more London Dispersion Forces
with neighbouring hexane molecules
STRUCTURAL ISOMERS
Draw all of the structural isomers of heptane using
line structures:
STRUCTURAL ISOMERS
The longer the chain, the greater the number of
structural isomers
Number of Carbon Atoms
4
5
6
7
8
9
10
12
15
Number of Isomers
2
3
5
9
18
35
75
355
4347