Transcript NamingIsomers

Naming Branched Alkanes
Grade 11 Chemistry
Shelley MacGibbon
INDEX
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Substituents
Naming Branched Alkanes
Finding the Longest Chain
Numbering the Carbons
Identifying the Branches
Rules of Nomenclature
Naming Our Molecule
More Complex Example
Alkanes
Alkanes have all single bonds. They can
either be in a ‘straight chain’ or they can
have one or more substituents.
H
H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
H
Straight Chain Molecule
INDEX
Substituents
Substituents are any functional group which is not part of the
main chain. They look like branches.
H
H
H
H
H
H
C
C
C
C
C
H
H
CH3 H
H
H
Substituent of the main chain.
INDEX
Naming Branched Alkanes
1. Find the longest continuous chain of carbons in
the molecule.
2. Number the carbons in the main chain ONLY!
Start closest to the first branching point.
3. Identify all branches and assign each a number.
4. Name the molecule using the rules of
nomenclature.
INDEX
Finding the Longest Chain
It must be continuous. This means that you cannot
backtrack or lift your pencil from the paper.
CH3
H3C
Longest
chain
CH CH2 CH CH2 CH3
CH2
CH3
INDEX
Numbering the Carbons
Number only those carbons in the main chain.
Remember to start at the carbon closest to the
first branch point.
CH3
CH3
4
H3C
1
3
CH CH2 CH CH2 CH3
2
3
CH2
5
6
H3C
6
CH CH2 CH CH2 CH3
5
4
1
CH2
CH3
YES
2
CH3
NO
INDEX
Identifying the Branches
Identify all branches on the main chain, name
them, and assign them a number according to
what carbon they are attached to.
CH3
H3C
1
meth- group on Carbon #2
4
CH CH2 CH CH2 CH3
2
3
5
6
CH2
eth- group on Carbon #4
CH3
INDEX
Rules of Nomenclature
• All substituents’ names end in –yl Ex: methyl
• The number of the carbon the substituent is attached to goes in
front of the substituent name and is separated with a hyphen (-)
Ex: 2-methyl
• If there is more than one substituent, they are separated by a
hyphen. Ex: 2-methyl-3-ethyl
• When there is more than one substituent with the same name the
numbers of each of the carbons they are attached to are separated
by commas(,). A prefix which tells you how many of that
substituent there are must also be used. Ex: 2,4-dimethyl
Cont’d
Rules of Nomenclature (cont’d)
• When naming the molecule, always start
with the lowest number. Ex: 2-methyl-5propyl.
• After all branches have been named, the
very last substituent is written directly
before the name of the main chain.
Ex: 2-methyl-3-ethyldecane
INDEX
Naming Our Molecule
CH3
H3C
1
4
CH CH2 CH CH2 CH3
2
3
Main chain has 6 carbons  hexane
Methyl on carbon #2
Ethyl on carbon #4
5
6
CH2
CH3
Name: 2-methyl-4-ethylhexane
INDEX
More Complex Example
CH3
1 CH3
3
H2C
CH2
CH3
CH
4
CH 2 C
5
2
CH 2 CH
6
7
CH 2 CH 2 CH3
8
9
10
CH3 H3C CH
CH3
Name: 3,5-dimethyl-5-propyl-7-ethyldecane
INDEX