iupac nomenclature dr margaret a.l. blackie [email protected]
TRANSCRIPT
Naming of the Alkanes
Naming of the alkanes
2. Identify the longest unbroken carbon chain
8 – carbon chain7 – carbon chain
CH3 CH CH2 CH2 CH CH CH2 CH3
CH2
CH3
CH3 CH3
octane
base
1. Identify the main functional group
This step is not necessary for the alkanes – there is no functional group.
CH3 CH CH2 CH2 CH CH CH2 CH3
CH2
CH3
CH3 CH3
21 3 4 5 6 7 8
First substituent at carbon no. 2
3. Number the chain so that the first substituent has the lowest possible number
378 6 5 4 2 1
First substituent at position no. 3
Correct numbering: Substituents at 2, 5 and 6
NB: If the first substituent (side chain) has the same number, use the second substituent to separate the two etc …
CH3 CH CH2 CH2 CH CH CH2 CH3
CH2
CH3
CH3 CH3
21 3 4 5 6 7 8
4. Identify the substituents (side chains and the position on the main chain or ring)
2-methyl5-ethyl6-methyl
5. Use the prefixes (di-, tri-, tetra-) depending on the number of identical substituents bonded to the main chain
CH3 CH CH2 CH2 CH CH CH2 CH3
CH2
CH3
CH3 CH3
21 3 4 5 6 7 8
2-methyl5-ethyl6-methyl
2,6-dimethyl5-ethyl
CH3 CH CH2 CH2 CH CH CH2 CH3
CH2
CH3
CH3 CH3
21 3 4 5 6 7 8
6. Write down the side chains in alphabetical order, preceded by the number: (don’t write down di-, tri-, tetra-etc. in alphabetical order)
5-ethyl-2,6-dimethyloctane
Dimethyl comes after ethyl, because e is before m – the d of di is not considered.
5-ethyl-2,6-dimethyloctane
The name should not be separated (there are some exceptions which will be addressed later.)
Dimethyloctane is written as one word
Numbers separated from words by a hyphen (N shows a position and is considered as a number when naming the amines and amides)
Numbers separated by a comma
Note: The name is WRONG if any one of these three rules are disobeyed!
5-ethyl-2-6-dimethyloctane5,ethyl,2,6,dimethyloctane
5-ethyl-2,6-dimethyl octane
Important: The name is WRONG if any one of these rules are disobeyed!
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
Name is wrong – There should be no space between dimethyl and octane
What is wrong with the names below?
Important points for purposes of explanation
CH3
CH3 CH2
CH CH2 CH
CH2 CH2 CH3
CH2 CH3
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
If there are two options for an unbroken carbon chain:Choose the chain with the most side chains as the base
CH3
CH3 CH2
CH CH2 CH
CH2 CH2 CH3
CH2 CH CH3
CH3
Three substituentsTwo substituents
Correct name: 2,6-dimethyl-4-propyloctaneIncorrect: 3-methyl-5-isobutyloctane
CH3 CH CH
CH3
CH2 CH CH3
CH3CH3
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.
CH3 CH CH
CH3
CH2 CH CH3
CH3CH31 2 3 4 5 6 6 5 4 3 2 1
First substituent is at position 2 in both numberings
Second substituent at positions 3 and 4 respectively.
Correct numbering
Correct name : 2,3,5-trimethylhexane
CH3 CH2 CH
CH3
CH CH2 CH3
CH2
CH3
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
CH3 CH2 CH
CH3
CH CH2 CH3
CH2
CH3
1 2 3 4 5 6
3-methyl-4-ethylhexane3-ethyl-4-methylhexane
6 5 4 3 2 1
Correct name
When a functional group occurs
Identifying the main functional group is the first step in naming the compound.
At grade 12 level the following step is unnecessary, but is included for educators.
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.
FUNCTIONAL GROUPSHighest 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
R OH
O
R OR'
O
R H
O
R R'
O
R OH
R C C R'
CH3 C CH CH CH3
O
Br
CH3
The highest priority group must get the lowest possible number
1 2 3 4 5
Number from left to right
Main functional group – ketone – suffix ‘one’
Longest unbroken carbon chain containing the main functional group – 5 carbons - ‘pentane’
Base – pentan-2-one
Subsituents: 3-bromo4-methyl
Correct name: 3-bromo-4-methylpentan-2-one
correct name: 3-bromo-4-methylpentan-2-one
CH3 C CH CH CH3
O
Br
CH3
1 2 3 4 5
3-bromo-4-methyl-2-pentanone is also acceptable
It is better to write the number directly in front of the main functional group
CH3 C CH C CH2
O
Br
CH3
Correct name: 3-bromo-4-methylpentan-2-one
CH3 C CH CH CH3
O
Br
CH3
1 2 3 4 5
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
Number or no number?
Main functional group : aldehyde – prefix ‘al’
correct name: Pentanal
CH2 CH2 CH2 CH OCH3
C CH2 CH2 CH3CH3
O
Main functional group: ketone – prefix ‘one’
correct name: Pentan-2-one
No number on the aldehyde because the carbonyl group must be on the first carbon
Number necessary because the carbonyl group can be at position 2 or 3
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.
Pentan-1-al is NOT acceptable
Number or no number?
CH3 CH
CH2
CH3 CH
CH CH3
correct name: But-2-ene
correct name: Propene
CH3 CH2
CH CH2
But-1-ene is a possibility, so the number is important.‘
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
Questions 1. On the previous slide But-2-ene and But-1-ene are called… ? 2. Give a brief explanation for the names given in question 1.3. Write down the molecular formula for the above compounds.4. Write down the structural formulae for 2 more possible structures.5. Name the structures completed in question 4.
Answers 1. ISOMERS2. Isomers are compounds with the same molecular formula but
different structural formulas .4. Write down the structural formulae for 2 more possible structures.
2-MethylPropene
C
CC
H
H
H H
HHH
H
CH2
CH3 C
C
HC
Cyclobutane
Carboxylic acids and derivatives
CH3
CH2
C O
OH
Carboxylic acids
Propanoic acid
CH3
CH2
C O
O-
Propanoate ion
CH3
CH2
C O
Cl
Propanoyl chloride (not for exam)
Esters
MethylpropanoateCH3 CH2 C
O
O CH3
Identify carboxylic acid that produces the ester
This part is named as with the corresponding ion - propanoate
Identify the substituent on the carboxylate oxygen
This part is named as the alkyl group – methyl