1. Dr Margaret A.L. Blackie mblackie@sun.ac.za
IUPAC nomenclature
Dr Margaret A.L. Blackie

2. Naming of the Alkanes

3. Naming of the alkanes 1. Identify the main functional group
This step is not necessary for the alkanes – there is no functional group.
Naming of the alkanes
1. Identify the main functional group
2. Identify the longest unbroken carbon chain
7 – carbon chain
8 – carbon chain
octane
base

4. NB: If the first substituent (side chain) has the same number, use the second substituent to separate the two etc …
3. Number the chain so that the first substituent has the lowest possible number 2 1 3 4 5 6 7 8 3 7 8 6 5 4 2 1
First substituent at carbon no. 2
First substituent at position no. 3
Correct numbering:
Substituents at 2, 5 and 6

5. 4. Identify the substituents (side chains and the position on the main chain or ring)2 1 3 4 5 6 7 8
2-methyl
5-ethyl
6-methyl

6. 5. Use the prefixes (di-, tri-, tetra-) depending on the number of identical substituents bonded to the main chain 2 1 3 4 5 6 7 8
2-methyl
5-ethyl
6-methyl
2,6-dimethyl
5-ethyl

7. 5-ethyl-2,6-dimethyloctane
6. Write down the side chains in alphabetical order, preceded by the number: (don’t write down di-, tri-, tetra-etc. in alphabetical order) 2 1 3 4 5 6 7 8
5-ethyl-2,6-dimethyloctane
Dimethyl comes after ethyl, because e is before m – the d of di is not considered.

8. 5-ethyl-2,6-dimethyloctane
The name should not be separated (there are some exceptions which will be addressed later.)
Numbers separated by a comma
Dimethyloctane is written as one word
5-ethyl-2,6-dimethyloctane
Numbers separated from words by a hyphen (N shows a position and is considered as a number when naming the amines and amides)
Note: The name is WRONG if any one of these three rules are disobeyed!

9. 5-ethyl-2,6-dimethyloctane
Important: The name is WRONG if any one of these rules are disobeyed!
5-ethyl-2,6-dimethyloctane
What is wrong with the names below?
5-ethyl-2-6-dimethyloctane
5,ethyl,2,6,dimethyloctane
Name is wrong – the hyphen between the numbers are incorrect
The name is wrong – the comma between a number and a word is incorrect
5-ethyl-2,6-dimethyl octane
Name is wrong – There should be no space between dimethyl and octane

10. Important points for purposes of explanation

11. The longest unbroken carbon chain is not necessarily straight
Longest straight chain contains only 5 carbons
Longest unbroken chain contains 8 carbons
Therefore the name is octane and not pentane

12. If there are two options for an unbroken carbon chain:
Choose the chain with the most side chains as the base
Two substituents
Three substituents
Correct name: 2,6-dimethyl-4-propyloctane
Incorrect: 3-methyl-5-isobutyloctane

13. Correct name : 2,3,5-trimethylhexane
If there is no difference in the number of the position of the first side chain, look at the following side chain, if there is no difference at the second, look at the third, etc. 1 2 3 4 5 6 6 5 4 3 2 1
Correct numbering
First substituent is at position 2 in both numberings
Second substituent at positions 3 and 4 respectively.
Correct name : 2,3,5-trimethylhexane

14. 3-methyl-4-ethylhexane 3-ethyl-4-methylhexane
When there is no difference in the numbers of the positions of the substituents : choose the numbers according to alphabetical order of the substituents, that is the first substituent alphabetically gets the lowest number 1 2 3 4 5 6 6 5 4 3 2 1
3-methyl-4-ethylhexane
3-ethyl-4-methylhexane
Correct name

15. When a functional group occurs

16. At grade 12 level the following step is unnecessary, but is included for educators.
Identifying the main functional group is the first step in naming the compound.
Functional groups are prioritised according a list (see next slide)
The main functional group is the functional group with the highest priority.
The base is the longest unbroken carbon chain containing the main functional group.

17. General name General structure Name as suffix Carboxylic acid
FUNCTIONAL GROUPS
Highest to lowest priority
General name
General structure
Name as suffix
Carboxylic acid
-oic acid
Ester
-oate
Aldehyde
-al
Ketone
-one
Alcohol
-ol
Alkene
-ene
Alkyne
-yne

18. The highest priority group must get the lowest possible number
Subsituents:
3-bromo
4-methyl 1 2 3 4 5
Base – pentan-2-one
Number from left to right
Main functional group – ketone – suffix ‘one’
Longest unbroken carbon chain containing the main functional group – 5 carbons - ‘pentane’
Correct name:
3-bromo-4-methylpentan-2-one

19. 3-bromo-4-methylpentan-2-one1 2 3 4 5
correct name:
3-bromo-4-methylpentan-2-one
3-bromo-4-methyl-2-pentanone is also acceptable
It is better to write the number directly in front of the main functional group

20. 3-bromo-4-methylpent-4-ene-2-one1 2 3 4 5
Correct name:
3-bromo-4-methylpentan-2-one
Consider:
Main functional group – ketone – prefix ‘one’
Longest unbroken carbon chain containing the main functional group – 5 carbons – unsaturated chain - ‘pentene’-
Base – pent-4-ene-2-one
correct name:
3-bromo-4-methylpent-4-ene-2-one

21. correct name: Pentan-2-one
Number or no number?
Number necessary because the carbonyl group can be at position 2 or 3
Main functional group: ketone – prefix ‘one’
correct name: Pentan-2-one
Pentan-1-al is NOT acceptable
No number on the aldehyde because the carbonyl group must be on the first carbon
Main functional group : aldehyde – prefix ‘al’
correct name: Pentanal
Revise: the main functional group always gets the lowest possible number. The carbonyl group is always at the end or beginning of the chain, therefore it must be in position number 1.

22. Number or no number? correct name: But-2-ene correct name: Propene
But-1-ene is a possibility, so the number is important.‘
correct name: But-2-ene
There is no alternative, propene is prop-1-ene
The locant is redundant in this particular case and should be dropped.
The redundancy is associated with this particular molecule not the nature of the functional group so inclusion of the locant is acceptable
correct name: Propene

23. Questions Answers 2-MethylPropene Cyclobutane
On the previous slide But-2-ene and But-1-ene are called… ?
Give a brief explanation for the names given in question 1.
Write down the molecular formula for the above compounds.
Write down the structural formulae for 2 more possible structures.
Name the structures completed in question 4.
Answers
ISOMERS
Isomers are compounds with the same molecular formula but different structural formulas .
4. Write down the structural formulae for 2 more possible structures. C H 2 3
2-MethylPropene
Cyclobutane

24. Carboxylic acids and derivatives
Propanoic acid
Propanoate ion
Propanoyl chloride (not for exam)

25. Esters Methylpropanoate
Identify carboxylic acid that produces the ester
This part is named as with the corresponding ion - propanoate
Methylpropanoate
Identify the substituent on the carboxylate oxygen
This part is named as the alkyl group – methyl
Esters