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Naming questions look like free marks, and that is why they hurt. One wrong locant or a prefix in the wrong order and the answer is wrong, with no part credit in a multiple-choice paper. The fix is to use the same order of steps every time. This post gives you that order, works through five names, shows the slips examiners look for, and explains one place where the textbook and the latest IUPAC rules disagree.
What naming does the syllabus expect?
The JEE (Main) 2026 syllabus lists "Nomenclature (Trivial and IUPAC)" in Some Basic Principles of Organic Chemistry, and IUPAC nomenclature again under hydrocarbons and other compound classes. The method is set out in the NCERT Class 11 chapter on organic chemistry basics. Check the syllabus for your exam year.
The five-step method
Find the principal functional group. It becomes the suffix. NCERT gives the order of decreasing priority as -COOH, -SO3H, -COOR, -COCl, -CONH2, -CN, -CHO, >C=O, -OH, -NH2, then C=C and C≡C. Lower-priority groups become prefixes (hydroxy-, amino-, oxo-).
Choose the parent chain. In NCERT, this is the longest carbon chain that contains the principal functional group, and for alkenes the longest chain containing the double bond.
Number the chain so that the principal group gets the lowest locant, then multiple bonds, then substituents.
Name and order the substituents alphabetically. Multiplying prefixes (di-, tri-) are ignored when alphabetising. NCERT notes that iso- and neo- count as part of the name, while sec- and tert- do not.
Assemble with commas between numbers and hyphens between numbers and letters.
How do you choose the lowest locants?
Use the first point of difference. Write both numbering directions as sets and compare them term by term. The first place they differ decides it.
Worked example 1. A decane chain carries methyl groups on carbons that number 2, 7 and 8 from one end, or 3, 4 and 9 from the other. Compare: 2 against 3. The first set wins, so the name is 2,7,8-trimethyldecane. Notice that the sum of the first set (17) is larger than the second (16). The sum-of-locants rule many students use gives the wrong answer here.
Worked example 2. (CH3)3C-CH2-CH(CH3)-CH3. The longest chain has five carbons. From the left the methyls are at 2, 2 and 4. From the right they are at 2, 4 and 4. First point of difference: 2 against 4 in the second position. The name is 2,2,4-trimethylpentane.
How do you order substituents?
Worked example 3. CH3-CH(CH3)-CH2-CH(C2H5)-CH2-CH3. The parent chain has six carbons. Numbering from the left puts the methyl at 2 and the ethyl at 4, giving the set {2, 4}. From the right, ethyl is at 3 and methyl at 5, giving {3, 5}. So the locants are 2 and 4. Alphabetically, ethyl comes before methyl, so the name is 4-ethyl-2-methylhexane, not 2-methyl-4-ethylhexane.
How do you name compounds with two functional groups?
Worked example 4. CH3-CH(OH)-CH2-CHO. Aldehyde outranks alcohol, so the suffix is -al and -OH becomes the prefix hydroxy-. The aldehyde carbon is C1. Counting along, the OH is on C3. The name is 3-hydroxybutanal.
Worked example 5. CH2=CH-CH2-COOH. The carboxylic acid is the principal group and its carbon is C1. The double bond starts at C3. The name is but-3-enoic acid.
Where do NCERT and the 2013 IUPAC rules differ?
IUPAC publishes the official rules in its "Blue Book", most recently as Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. In section P-44.3, it reverses an older rule: when choosing the principal chain, chain length now comes before unsaturation. An eight-carbon saturated chain is now senior to a seven-carbon chain with a double bond.
NCERT still teaches the older approach, choosing the longest chain that contains the double bond. For board and JEE answers, follow NCERT and your exam's past answer keys. Knowing the change helps when a reference book or website gives a different name for the same branched alkene.
Common slips and how to avoid them
Using the sum of locants instead of the first point of difference.
Alphabetising with di-, tri-, as in placing "dimethyl" under d.
Numbering from the substituent end when a functional group is present. The principal group gets priority.
Counting the carbon of -CHO, -COOH or -CN in the chain, then forgetting it is C1.
Missing a longer chain hidden in a branch. Trace every path before choosing.
Does practising naming actually help?
Yes, and the type of practice matters. Over five years of an organic chemistry course in South Korea, Justin Fendos (2021) added jigsaw group work, rule-based learning and retrieval practice to an organic chemistry course. Together, the three gave substantial improvements on both name-to-structure and structure-to-name questions. You can copy the retrieval part on your own: test yourself in both directions instead of rereading lists.
A practice routine for naming
Write the priority order and the five steps from memory.
Name ten structures, then draw ten structures from names. Both directions matter.
Make a slip list from your errors, using the categories above.
Repeat with new examples after two days, then after a week.
Naming of complexes uses a separate set of rules; see our guide to naming coordination compounds. For the next layer of organic naming, read our post on stereoisomerism. When you get a name wrong and cannot see why, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer.
Today, draw one branched chain of your own where the sum of locants and the first point of difference give different answers, and name it correctly.
