In the previous section, we saw the naming procedure for hydrocarbons with more than one branch. In this section, we will see a special case coming under it.
This special case can be written as:
An example is given below in fig.14.23:
We will first name it using the usual procedure:
Step 1: The longest chain is highlighted in red colour in fig.14.24 below. It is the main chain:
Step 2:
• There are two branches. Both are Methyl
• In fig.14.24(a), the numbering is done from left to right
♦ In this numbering, the first branch is the left methyl radical and it gets number 2
• In fig.14.24(b), the numbering is done from right to left
♦ In this numbering, the first branch is the methyl radical on the right and it gets number 4
So the numbering in fig.14.24(a) is correct
♦ Position of the first branch is 2
♦ Position of the second branch is 4
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 7
♦ So the word root is hept
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 4
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[4-methyl]
+heptane
So the methyl radical is repeating. Based on what we have seen so far, the name would be:
2-Methyl-4-methylheptane.
But . . .
• If a branch comes two times, it's name should not be written two times
♦ Instead, the prefix 'di' should be used
• If a branch comes three times, it's name should not be written three times
♦ Instead, the prefix 'tri' should be used
• If a branch comes four times, it's name should not be written four times
♦ Instead, the prefix 'tetra' should be used
so on . . .
• The positions should be separated by commas
So the name of our compound is:
2,4-Dimethylheptane
Another example:
We will first name it using the usual procedure:
Step 1: The longest chain is highlighted in red colour in fig.14.26 below. It is the main chain:
Step 2:
• There are two branches. Both are Methyl
• In fig.14.26(a), the numbering is done from left to right
♦ In this numbering, the first branch is the left methyl radical and it gets number 2
• In fig.14.26(b), the numbering is done from right to left
♦ In this numbering, the first branch is the methyl radical on the right and it gets number 2
So the numbering in both fig.14.24(a)&(b) are correct
♦ Position of the first branch is 2
♦ Position of the second branch is 4
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 5
♦ So the word root is pent
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 4
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[4-methyl]
+pentane
So the methyl radical is repeating. Based on what we have seen in previous sections, the name would be:
2-Methyl-4-methylpentane
But as we have seen in the first example above in this section,
• If a branch comes two times, it's name should not be written two times
♦ Instead, the prefix 'di' should be used
• If a branch comes three times, it's name should not be written three times
♦ Instead, the prefix 'tri' should be used
• If a branch comes four times, it's name should not be written four times
♦ Instead, the prefix 'tetra' should be used
so on . . .
• The positions should be separated by commas
So the name of our compound is:
2,4-Dimethylpentane
In the next section, we will see a summary of what we have seen so far in this chapter. We will also see some solved examples.
This special case can be written as:
• The hydrocarbon has more than one branch
♦ Some of those branches are repeated
|
|---|
 |
| Fig.14.23 |
Step 1: The longest chain is highlighted in red colour in fig.14.24 below. It is the main chain:
 |
| Fig.14.24 |
• There are two branches. Both are Methyl
• In fig.14.24(a), the numbering is done from left to right
♦ In this numbering, the first branch is the left methyl radical and it gets number 2
• In fig.14.24(b), the numbering is done from right to left
♦ In this numbering, the first branch is the methyl radical on the right and it gets number 4
So the numbering in fig.14.24(a) is correct
♦ Position of the first branch is 2
♦ Position of the second branch is 4
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 7
♦ So the word root is hept
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 4
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[4-methyl]
+heptane
So the methyl radical is repeating. Based on what we have seen so far, the name would be:
2-Methyl-4-methylheptane.
But . . .
• If a branch comes two times, it's name should not be written two times
♦ Instead, the prefix 'di' should be used
• If a branch comes three times, it's name should not be written three times
♦ Instead, the prefix 'tri' should be used
• If a branch comes four times, it's name should not be written four times
♦ Instead, the prefix 'tetra' should be used
so on . . .
• The positions should be separated by commas
So the name of our compound is:
2,4-Dimethylheptane
Another example:
 |
| Fig.14.25 |
Step 1: The longest chain is highlighted in red colour in fig.14.26 below. It is the main chain:
 |
| Fig.14.26 |
• There are two branches. Both are Methyl
• In fig.14.26(a), the numbering is done from left to right
♦ In this numbering, the first branch is the left methyl radical and it gets number 2
• In fig.14.26(b), the numbering is done from right to left
♦ In this numbering, the first branch is the methyl radical on the right and it gets number 2
So the numbering in both fig.14.24(a)&(b) are correct
♦ Position of the first branch is 2
♦ Position of the second branch is 4
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 5
♦ So the word root is pent
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 4
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[4-methyl]
+pentane
So the methyl radical is repeating. Based on what we have seen in previous sections, the name would be:
2-Methyl-4-methylpentane
But as we have seen in the first example above in this section,
• If a branch comes two times, it's name should not be written two times
♦ Instead, the prefix 'di' should be used
• If a branch comes three times, it's name should not be written three times
♦ Instead, the prefix 'tri' should be used
• If a branch comes four times, it's name should not be written four times
♦ Instead, the prefix 'tetra' should be used
so on . . .
• The positions should be separated by commas
So the name of our compound is:
2,4-Dimethylpentane
We will now see an interesting case:
Consider the compound shown in fig.14.27 below:
Let us name it by the usual procedure:
Step 1: The longest chain is highlighted in red colour in fig.14.28 below. It is the main chain:
Step 2:
• There are three branches. All are Methyl
• In fig.14.28(a), the numbering is done from left to right
♦ In this numbering, the first branch is the left methyl radical and it gets number 2
• In fig.14.28(b), the numbering is done from right to left
♦ In this numbering, the first branch is the methyl radical on the right and it gets number 2
• The numbering in both fig.14.28(a)&(b) seems to be correct
From fig.14.28(a), we get:
♦ Position of the first branch is 2
♦ Position of the second branch is 4
♦ Position of the second branch is 5
From fig.14.28(b), we get:
♦ Position of the first branch is 2
♦ Position of the second branch is 3
♦ Position of the second branch is 5
■ So we have a situation:
• Two methods of numbering gives the same number for the first branch
• In such a situation, we must consider the second branch. That second branch must get the lowest number.
• In our case, the numbering in fig.14.28(b) gives a lower number for the second branch. So it is correct
• The method in fig.14.28(a) is wrong. So an '×' mark is given above it.
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 6
♦ So the word root is hex
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 3
♦ methyl at position 5
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[3-methyl]
+hyphen
+[5-methyl]
+hexane
• So the methyl radical is repeating. Based on what we have seen in previous sections, the name would be:
2-Methyl-3-methyl-5-methylhexane
• Base on IUPAC rules that we saw in this section, we get:
2,3,5-Trimethylhexane.
Another example in this category:
Consider the compound shown in fig.14.29 below:
Let us name it by the usual procedure:
Step 1: The longest chain is highlighted in red colour in fig.14.30 below. It is the main chain:
Step 2:
• There are three branches. All are Methyl
• In fig.14.30(a), the numbering is done from left to right
♦ In this numbering, the first branch is the left methyl radical and it gets number 2
• In fig.14.30(b), the numbering is done from right to left
♦ In this numbering, the first branch is the methyl radical on the right and it gets number 2
• The numbering in both fig.14.30(a)&(b) seems to be correct
From fig.14.30(a), we get:
♦ Position of the first branch is 2
♦ Position of the second branch is 3
♦ Position of the second branch is 6
From fig.14.28(b), we get:
♦ Position of the first branch is 2
♦ Position of the second branch is 5
♦ Position of the second branch is 6
■ So we have a situation:
• Two methods of numbering gives the same number for the first branch
• In such a situation, we must consider the second branch. That second branch must get the lowest number.
• In our case, the numbering in fig.14.30(a) gives a lower number for the second branch. So it is correct
• The method in fig.14.30(b) is wrong. So an '×' mark is given above it.
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 7
♦ So the word root is hept
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 3
♦ methyl at position 6
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[3-methyl]
+hyphen
+[6-methyl]
+heptane
• So the methyl radical is repeating. Based on what we have seen in previous sections, the name would be:
2-Methyl-3-methyl-6-methylheptane
• Based on IUPAC rules that we saw in this section, we get:
2,3,6-Trimethylheptane.
Next we will see another interesting case in this category
Consider the compound shown in fig.14.31 below:
Let us name it by the usual procedure:
Step 1: The longest chain is highlighted in red colour in fig.14.32 below. It is the main chain:
Step 2:
• There are two branches. Both are Methyl
• In fig.14.32(a), the numbering is done from left to right
♦ In this numbering, both the branches get the number 2
• In fig.14.32(b), the numbering is done from right to left
♦ In this numbering, both the branches get the number 2
• The numbering in both fig.14.32(a)&(b) are correct
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 3
♦ So the word root is prop
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 2
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[2-methyl]
+hyphen
+propane
• So the methyl radical is repeating. Based on what we have seen in previous sections, the name would be:
2-Methyl-2-methylpropane
• Base on IUPAC rules that we saw in this section, we get:
2,2-Dimethylhexane.
That is., if two identical branches have the same position number, then that number should be repeated.
Let us see another example:
• The numbering options are shown in fig.14.34 below:
• The reader may write the steps in his/her own notebooks. The IUPAC name of this compound is:
2,2,3-Trimethylpentane
Consider the compound shown in fig.14.27 below:
 |
| Fig.14.27 |
Step 1: The longest chain is highlighted in red colour in fig.14.28 below. It is the main chain:
 |
| Fig.14.28 |
• There are three branches. All are Methyl
• In fig.14.28(a), the numbering is done from left to right
♦ In this numbering, the first branch is the left methyl radical and it gets number 2
• In fig.14.28(b), the numbering is done from right to left
♦ In this numbering, the first branch is the methyl radical on the right and it gets number 2
• The numbering in both fig.14.28(a)&(b) seems to be correct
From fig.14.28(a), we get:
♦ Position of the first branch is 2
♦ Position of the second branch is 4
♦ Position of the second branch is 5
From fig.14.28(b), we get:
♦ Position of the first branch is 2
♦ Position of the second branch is 3
♦ Position of the second branch is 5
■ So we have a situation:
• Two methods of numbering gives the same number for the first branch
• In such a situation, we must consider the second branch. That second branch must get the lowest number.
• In our case, the numbering in fig.14.28(b) gives a lower number for the second branch. So it is correct
• The method in fig.14.28(a) is wrong. So an '×' mark is given above it.
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 6
♦ So the word root is hex
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 3
♦ methyl at position 5
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[3-methyl]
+hyphen
+[5-methyl]
+hexane
• So the methyl radical is repeating. Based on what we have seen in previous sections, the name would be:
2-Methyl-3-methyl-5-methylhexane
• Base on IUPAC rules that we saw in this section, we get:
2,3,5-Trimethylhexane.
Another example in this category:
Consider the compound shown in fig.14.29 below:
 |
| Fig.14.29 |
Step 1: The longest chain is highlighted in red colour in fig.14.30 below. It is the main chain:
 |
| Fig.14.30 |
• There are three branches. All are Methyl
• In fig.14.30(a), the numbering is done from left to right
♦ In this numbering, the first branch is the left methyl radical and it gets number 2
• In fig.14.30(b), the numbering is done from right to left
♦ In this numbering, the first branch is the methyl radical on the right and it gets number 2
• The numbering in both fig.14.30(a)&(b) seems to be correct
From fig.14.30(a), we get:
♦ Position of the first branch is 2
♦ Position of the second branch is 3
♦ Position of the second branch is 6
From fig.14.28(b), we get:
♦ Position of the first branch is 2
♦ Position of the second branch is 5
♦ Position of the second branch is 6
■ So we have a situation:
• Two methods of numbering gives the same number for the first branch
• In such a situation, we must consider the second branch. That second branch must get the lowest number.
• In our case, the numbering in fig.14.30(a) gives a lower number for the second branch. So it is correct
• The method in fig.14.30(b) is wrong. So an '×' mark is given above it.
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 7
♦ So the word root is hept
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 3
♦ methyl at position 6
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[3-methyl]
+hyphen
+[6-methyl]
+heptane
• So the methyl radical is repeating. Based on what we have seen in previous sections, the name would be:
2-Methyl-3-methyl-6-methylheptane
• Based on IUPAC rules that we saw in this section, we get:
2,3,6-Trimethylheptane.
Next we will see another interesting case in this category
Consider the compound shown in fig.14.31 below:
 |
| Fig.14.31 |
Step 1: The longest chain is highlighted in red colour in fig.14.32 below. It is the main chain:
 |
| Fig.14.32 |
• There are two branches. Both are Methyl
• In fig.14.32(a), the numbering is done from left to right
♦ In this numbering, both the branches get the number 2
• In fig.14.32(b), the numbering is done from right to left
♦ In this numbering, both the branches get the number 2
• The numbering in both fig.14.32(a)&(b) are correct
Step 3:
• The 'finalized number of carbon atoms in the main chain' is 3
♦ So the word root is prop
• All the carbon-carbon bonds in the molecule are single bonds
♦ So the suffix is ane
Step 4:
• The names of the alkyl radicals which come as branches are:
♦ methyl at position 2
♦ methyl at position 2
Step 5:
Assembling the name:
[2-methyl]
+hyphen
+[2-methyl]
+hyphen
+propane
• So the methyl radical is repeating. Based on what we have seen in previous sections, the name would be:
2-Methyl-2-methylpropane
• Base on IUPAC rules that we saw in this section, we get:
2,2-Dimethylhexane.
That is., if two identical branches have the same position number, then that number should be repeated.
Let us see another example:
 |
| Fig.14.33 |
 |
| Fig.14.34 |
2,2,3-Trimethylpentane
In the next section, we will see a summary of what we have seen so far in this chapter. We will also see some solved examples.
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