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When we name compounds by following some definite set of rules then it is called nomenclature. Three primary things are necessary for naming a compound. These three things are:
- Find the parent chain of compounds (longest hydrocarbon).
- To form the suffix, find the functional group.
- To form the prefix, find the substituents.
Suffix or prefixes are formed by the functional group depending upon their priority series. The most commonly used nomenclature throughout the world is the one proposed and developed by the International Union of Pure and Applied Chemistry.
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Key Terms: Organic chemistry, Nomenclature, Carbon, Hydrocarbon, Halogen, Triple bonds, Double bonds, Atoms
Rules of Nomenclature
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The step-by-step rules for Nomenclature are the following:
Step 1: First of all, we need to find the longest chain of carbon for the compound.
Step 2: The numbering for the chain of carbon should be done in such a way that carbon atoms (s) that contain the halogen(s) or the X group must have the least possible number. And the carbon that contains double or triple bonds is given the lowest number.
Step 3: The presented multiple halogen atoms in the compound are named in Greek numerical prefixes such as tri, di, and tetra, etc to the same halogen forms of atoms of the total number attached to the carbon atom. When we join more than one halogen atom with the carbon atom, then the numeral will repeat that many times.
Step 4: If in the same compound, the various halogen groups are present then they are named in ascending order by following the alphabets.
Step 5: The halogen atom’s position in the compound is indicated by writing the name and the position of the halogen just before the name of the parent (origin) hydrocarbon.
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| Nucleophilic Substitution | Grignard Reagent | Enantiomers |
| Wurtz Reaction | Finkelstein Reaction | Mitsunobu Reaction |
How do I write the names?
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The two methodologies of writing names are the following:
- For the parent (origin) hydrocarbon depending upon the total number of carbon atoms in the longest chain of carbons try to write the root word.
- Calculate the total number of halogen atoms that are present. If multiple halogen atoms present then you need to arrange the halogens in the prefix alphabetically and label them in their respective position. But if more than one time, the same halogen atom is present then use tri, di, tetra prefixes.
Nomenclature of Haloalkanes
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Haloalkane is commonly known as an alkyl halide. The haloalkane written format in IUPAC name is “numerical position-alphabetically placed halo- root-word-ane”
Nomenclature of Haloalkanes
Nomenclature of Haloarenes
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Haloarene is commonly known as Aryl Halide. In the system of nomenclature, depending on the basic position of the halogen atom in the aromatic ring the numerical prefixes are named.
When more than one halogen atom is present, then the halogen group is named and the aromatic ring is numbered based on the numerical position of the aromatic ring. The writing format of numerical prefixes are (1, 2) ; (1,3) ; (1,4). Always the lowest number is given to the halogen number.
Nomenclature of Haloarenes
Nomenclature of Some Compounds
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IUPAC Name of the compound: 1 − Bromo − 2,2 – dimethylpropane. The common name of the compound: neo − Pentylbromide.
CH2 = CH – CH2Br
- IUPAC Name of the compound: − 3 – Bromoprop – 1 – ene. Common Name of the compound: Allyl Bromide.
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Sample Questions
Ques. What do you mean by the nomenclature of organic compounds?(1 mark)
Ans. The naming method of organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC) is called Nomenclature of organic compounds.
Ques. How to use commas in nomenclature?(1 mark)
Ans. In nomenclature, commas are used between dashes and numbers in between numbers and letters.
Ques. Why is nomenclature so important?(1 mark)
Ans. Nomenclature is so important to distinguish between inorganic and organic compounds.
Ques. What is the first rule of nomenclature?(1 mark)
Ans. To find the longest chain of carbon for the compound is the first rule of nomenclature.
Ques. Who established nomenclature?(1 mark)
Ans. Linnaeus established the practice of nomenclature for the first time.
Previous Year Questions
Ques 1. Write the IUPAC name of the following: (2018)
Ans. 3, 3- Dimethyl-pentane-2-oI is the IUPAC name.
Ques 2. a) Identify the chiral molecule in the following pair:
(b) Write the structure of the product when chlorobenzene is treated with methyl chloride in the presence of sodium metal and dry ether.
(c) Write the structure of the alkene formed by dehydrohalogenation of 1-Bromo-1 methylcyclohexane with alcoholic KOH. (2018)
Ans.
- The (i) image is that of the chiral molecule.
- When chlorobenzene is treated with methyl chloride in the presence of sodium metal and dry ether the product is known to be as toluene. The reaction is known to be as the Wurtz-Fitting reaction.
- The structure of the alkene formed by dehydrohalogenation of 1-Bromo-1 methylcyclohexane with alcoholic KOH is as follows:
Ques 3. Give the IUPAC names of the following: (2014C)
Ans.
i) Bromobutane
ii) 1, 3-Dibromobenzene
iii) 3-Chloropropene
Ques 4. Draw the structure of 2-bromopentane. (2014C)
Ans.
Ques 5. Write the IUPAC name of: (2013)
Ans.
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