In the previous section, we saw the naming procedure for hydrocarbons with repeating branches. In this section, we will see a summary of the various cases that we have seen so far in this chapter.
• Later in this section, we will see how to do a reverse process. That is., when we are given an IUPAC name, we will see how to draw it's structure
The various cases that we saw so far, can be presented in the form of a flow chart as shown in fig.14.35 below:
Now we will see some solved examples related to the 'Branched chain' case as a whole:
Solved example 14.4
Write the IUPAC names of the four compounds shown in fig.14.36 below:
Solution:
The fig.14.37 below shows the required markings. Based on that, the naming can be done easily.
The compounds are:
1. 3-Methylhexane
2. 2,4-Dimethylpentane
3. 3,3-Diethylpentane
4. 3,4-Diethylhexane
• The reader may try different numbering options and write the steps in his/her own notebooks.
Solved example 14.5
Write the IUPAC names of the four compounds shown in fig.14.38 below:
Solution:
The fig.14.39 below shows the required markings. Based on that, the naming can be done easily.
The compounds are:
1. 3-Ethyl-2-methylhexane
2. 2,3,5-Trimethylhexane
3. 3,4-Dimethylhexane
4. 4-Ethyl-2,3-Dimethylhexane
• The reader may try different numbering options and write the steps in his/her own notebooks.
■ Now we will see a reverse process. That is:
We will be given the IUPAC name of a hydrocarbon. We must draw the structure of that hydrocarbon.
• We will analyse the process using an example:
Consider 2,3-Dimethylbutane. We will try to draw it's structure using the following steps:
Step 1: Note the 'word root+suffix'. It is 'butane'
• From this, we get two information:
♦ There are 4 carbon atoms in the main chain
♦ All the carbon-carbon bonds are 'single bonds'
• So we can draw the main chain in this step 1.
• The 'numbering of carbon atoms in the main chain' can also be done at this stage.
• This is shown in fig.14.40(a) below:
Step 2: Note the branches and their positions. We have: '2,3-Dimethyl'
• From this we get the following information:
♦ There are two branches.
♦ Both are methyl radicals
♦ Their positions are at 2 and 3
• So the two branches can be attached to the main chain that we obtained in step 1
• The result is shown in fig.14.40(b) above
Step 3: This is the final step.
• Fill all the valencies of carbon atoms.
• Since it is a hydrocarbon, only carbon and hydrogen will be present.
♦ So we use hydrogen to fill up the valencies.
• The result is shown in fig.14.40(c) above. So this fig.14.40(c) shows the required structure
Another example: 4-Ethyl-3,3-dimethylheptane
Step 1: Note the 'word root+suffix'. It is 'heptane'
• From this, we get two information:
♦ There are 7 carbon atoms in the main chain
♦ All the carbon-carbon bonds are 'single bonds'
• So we can draw the main chain in this step 1.
• The 'numbering of carbon atoms in the main chain' can also be done at this stage.
• This is shown in fig.14.41(a) below:
Step 2: Note the branches and their positions. We have: '4-Ethyl and 3,3-Dimethyl'
• From this we get the following information:
♦ There are three branches.
♦ One ethyl radical and two methyl radicals
♦ The ethyl radical is at 4
♦ Both the methyl radicals are at position 3
• So the three branches can be attached to the main chain that we obtained in step 1
• The result is shown in fig.14.41(b) above
Step 3: This is the final step.
• Fill all the valencies of carbon atoms.
• Since it is a hydrocarbon, only carbon and hydrogen will be present.
♦ So we use hydrogen to fill up the valencies.
• The result is shown in fig.14.41(c) above. So this fig.14.41(c) shows the required structure
• Note that, there are no hydrogen atoms attached to the carbon atom at position 3 (there are two branches at position 3)
• Also, there is only one hydrogen atom attached to the carbon atom at position 4 (there is only one branch at position 4)
One more example: 3,3-Diethylpentane
Step 1: Note the 'word root+suffix'. It is 'pentane'
• From this, we get two information:
♦ There are 5 carbon atoms in the main chain
♦ All the carbon-carbon bonds are 'single bonds'
• So we can draw the main chain in this step 1.
• The 'numbering of carbon atoms in the main chain' can also be done at this stage.
• This is shown in fig.14.42(a) below:
Step 2: Note the branches and their positions. We have: '3,3-Diethyl'
• From this we get the following information:
♦ There are two branches.
♦ Both are ethyl radicals
♦ Both the ethyl radicals are at position 3
• So the two branches can be attached to the main chain that we obtained in step 1
• The result is shown in fig.14.42(b) above
Step 3: This is the final step.
• Fill all the valencies of carbon atoms.
• Since it is a hydrocarbon, only carbon and hydrogen will be present.
♦ So we use hydrogen to fill up the valencies.
• The result is shown in fig.14.41(c) above. So this fig.14.41(c) shows the required structure
• Note that, there are no hydrogen atoms attached to the carbon atom at position 3 (there are two branches at position 3)
In the next section, we will see Nomenclature of Unsaturated hydrocarbons.
• Later in this section, we will see how to do a reverse process. That is., when we are given an IUPAC name, we will see how to draw it's structure
The various cases that we saw so far, can be presented in the form of a flow chart as shown in fig.14.35 below:
 |
| Fig.14.35 |
Solved example 14.4
Write the IUPAC names of the four compounds shown in fig.14.36 below:
 |
| Fig.14.36 |
The fig.14.37 below shows the required markings. Based on that, the naming can be done easily.
 |
| Fig.14.37 |
1. 3-Methylhexane
2. 2,4-Dimethylpentane
3. 3,3-Diethylpentane
4. 3,4-Diethylhexane
• The reader may try different numbering options and write the steps in his/her own notebooks.
Solved example 14.5
Write the IUPAC names of the four compounds shown in fig.14.38 below:
 |
| Fig.14.38 |
The fig.14.39 below shows the required markings. Based on that, the naming can be done easily.
 |
| Fig.14.39 |
1. 3-Ethyl-2-methylhexane
2. 2,3,5-Trimethylhexane
3. 3,4-Dimethylhexane
4. 4-Ethyl-2,3-Dimethylhexane
• The reader may try different numbering options and write the steps in his/her own notebooks.
Structure from IUPAC name
• So far, we have been discussing how to give appropriate names when the structure of various hydrocarbons are given.■ Now we will see a reverse process. That is:
We will be given the IUPAC name of a hydrocarbon. We must draw the structure of that hydrocarbon.
• We will analyse the process using an example:
Consider 2,3-Dimethylbutane. We will try to draw it's structure using the following steps:
Step 1: Note the 'word root+suffix'. It is 'butane'
• From this, we get two information:
♦ There are 4 carbon atoms in the main chain
♦ All the carbon-carbon bonds are 'single bonds'
• So we can draw the main chain in this step 1.
• The 'numbering of carbon atoms in the main chain' can also be done at this stage.
• This is shown in fig.14.40(a) below:
 |
| Fig.14.40 |
• From this we get the following information:
♦ There are two branches.
♦ Both are methyl radicals
♦ Their positions are at 2 and 3
• So the two branches can be attached to the main chain that we obtained in step 1
• The result is shown in fig.14.40(b) above
Step 3: This is the final step.
• Fill all the valencies of carbon atoms.
• Since it is a hydrocarbon, only carbon and hydrogen will be present.
♦ So we use hydrogen to fill up the valencies.
• The result is shown in fig.14.40(c) above. So this fig.14.40(c) shows the required structure
Another example: 4-Ethyl-3,3-dimethylheptane
Step 1: Note the 'word root+suffix'. It is 'heptane'
• From this, we get two information:
♦ There are 7 carbon atoms in the main chain
♦ All the carbon-carbon bonds are 'single bonds'
• So we can draw the main chain in this step 1.
• The 'numbering of carbon atoms in the main chain' can also be done at this stage.
• This is shown in fig.14.41(a) below:
 |
| Fig.14.41 |
• From this we get the following information:
♦ There are three branches.
♦ One ethyl radical and two methyl radicals
♦ The ethyl radical is at 4
♦ Both the methyl radicals are at position 3
• So the three branches can be attached to the main chain that we obtained in step 1
• The result is shown in fig.14.41(b) above
Step 3: This is the final step.
• Fill all the valencies of carbon atoms.
• Since it is a hydrocarbon, only carbon and hydrogen will be present.
♦ So we use hydrogen to fill up the valencies.
• The result is shown in fig.14.41(c) above. So this fig.14.41(c) shows the required structure
• Note that, there are no hydrogen atoms attached to the carbon atom at position 3 (there are two branches at position 3)
• Also, there is only one hydrogen atom attached to the carbon atom at position 4 (there is only one branch at position 4)
One more example: 3,3-Diethylpentane
Step 1: Note the 'word root+suffix'. It is 'pentane'
• From this, we get two information:
♦ There are 5 carbon atoms in the main chain
♦ All the carbon-carbon bonds are 'single bonds'
• So we can draw the main chain in this step 1.
• The 'numbering of carbon atoms in the main chain' can also be done at this stage.
• This is shown in fig.14.42(a) below:
 |
| Fig.14.42 |
• From this we get the following information:
♦ There are two branches.
♦ Both are ethyl radicals
♦ Both the ethyl radicals are at position 3
• So the two branches can be attached to the main chain that we obtained in step 1
• The result is shown in fig.14.42(b) above
Step 3: This is the final step.
• Fill all the valencies of carbon atoms.
• Since it is a hydrocarbon, only carbon and hydrogen will be present.
♦ So we use hydrogen to fill up the valencies.
• The result is shown in fig.14.41(c) above. So this fig.14.41(c) shows the required structure
• Note that, there are no hydrogen atoms attached to the carbon atom at position 3 (there are two branches at position 3)
In the next section, we will see Nomenclature of Unsaturated hydrocarbons.
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