CBSE Class 11 & JEE Mains • Module 02 of 20 • The Universal Language of Chemistry
Topics Covered: 7-Step Naming Algorithm · Parent Chain Selection · Functional Group Priority Table · Prefix vs Suffix · Numbering Rules (lowest locant set) · Cyclic & Bicyclic Compounds · Naming Ionic & Ether Systems · Complex Structures with Multiple FGs
Organic chemistry has millions of compounds. Before IUPAC, every compound had a trivial (common) name — often with no logic. IUPAC (International Union of Pure and Applied Chemistry) created a systematic, universal naming system where:
Use the priority table. The highest-priority FG determines the suffix. All other FGs become prefixes.
Longest carbon chain that includes the principal FG and maximum double/triple bonds. This gives the root name (meth-/eth-/prop-/but-/pent- etc.).
Give the principal FG the lowest possible locant. If tie, number to give multiple bonds the lowest locant. If still tie, give substituents the lowest locant set.
All groups NOT in the principal chain = substituents. Alkyl groups: methyl, ethyl, propyl, isopropyl. Other FGs (when not principal): fluoro, chloro, oxo, hydroxy etc.
List substituents alphabetically BEFORE the root. Ignore multiplicative prefixes (di, tri) when alphabetizing.
di (×2), tri (×3), tetra (×4), penta (×5). For complex substituents: bis, tris, tetrakis.
Format: [locant-prefix]- [parent] -[locant][suffix]. Separate numbers from letters with hyphens, separate numbers from numbers with commas.
| Priority | Functional Group | Formula | Suffix | Prefix |
|---|---|---|---|---|
| 1 (High) | Carboxylic Acid | –COOH | -oic acid | carboxy– |
| 2 | Ester | –COOR | -oate (alkyl …oate) | alkoxycarbonyl– |
| 3 | Acid Halide | –COX | -oyl halide | haloformyl– |
| 4 | Amide | –CONH₂ | -amide | carbamoyl– |
| 5 | Nitrile | –CN | -nitrile / -carbonitrile | cyano– |
| 6 | Aldehyde | –CHO | -al | oxo– / formyl– |
| 7 | Ketone | C=O | -one | oxo– |
| 8 | Alcohol | –OH | -ol | hydroxy– |
| 9 | Amine | –NH₂ | -amine | amino– |
| 10 | Alkene | C=C | -ene | — |
| 11 (Low) | Alkyne | C≡C | -yne | — |
Structure: CH₃–CH(CH₃)–CH(CH₃)–CH₃
Step 1: No FG → alkane (suffix: -ane)
Step 2: Longest chain = 4C → root = but
Step 3: Number from end nearest to branches → C1-C2-C3-C4 (methyl groups at C2 and C3)
Step 4: Two methyl groups → prefix = 2,3-dimethyl
Name: 2,3-dimethylbutane
Reading from the diagram above:
Parent chain: 5C → pent. Principal FG = –OH → suffix -ol at C2. Branch: methyl at C4 → prefix 4-methyl.
Notice: We number from the end that gives OH the LOWEST locant (2 not 4). Then methyl is at C4.
If there are multiple substituents, number to give the locant set whose first point of difference is lower.
Example: 2,3,5 vs 2,4,5 — Compare at first difference: 3 vs 4 → choose 2,3,5 (lower at first point of difference).
For alkenes/alkynes, give the double/triple bond the lowest possible locant (if no FG suffix takes priority).
New IUPAC (2013): Locant immediately before suffix: hex-3-en-1-ol (not hex-3(en)-1(ol)).
For compounds with both C=C and C≡C: number to give lower locant to C=C over C≡C if both get same locants.
Add prefix cyclo– to the parent chain name.
Cyclopropane (3C ring), cyclobutane (4C), cyclopentane (5C), cyclohexane (6C).
If the ring has fewer carbons than an attached chain AND no FG, the chain becomes parent. If the ring has more carbons, the ring is parent.
| Name | Structure | When Used |
|---|---|---|
| Phenyl (Ph– or C₆H₅–) | Benzene ring with one free bond | Benzene ring as substituent |
| Benzyl (BnCH₂–) | C₆H₅–CH₂– | Phenylmethyl group |
| Vinyl (CH₂=CH–) | Ethenyl group | C=C as substituent |
| Allyl (CH₂=CHCH₂–) | Prop-2-en-1-yl | Allyl group |
| Isopropyl | (CH₃)₂CH– | 1-methylethyl |
| Neopentyl | (CH₃)₃CCH₂– | 2,2-dimethylpropyl |
Problem: Name: CH₂=CH–CH(OH)–CH₂–CH₂–COOH
Step 1: Functional groups: –COOH (acid) and –OH (alcohol) and C=C (alkene). Priority: COOH > OH > C=C. Principal FG = –COOH → suffix -oic acid.
Step 2: Chain containing COOH and C=C: count → 6 carbons total → root = hex.
Step 3: Number from COOH end (COOH = C1). C1=COOH, C2–C3–C4(OH)–C5=C6.
Wait — the C=C is at C5–C6, OH is at C4, COOH is at C1.
Step 4: Prefixes: 4-hydroxy (OH is prefix since COOH has higher priority). Suffix for C=C: -en at position 5.
Ex 1 E: Name: CH₃CH₂CH₂CH₂OH
Solution: 4C chain, –OH at C1 → butan-1-ol
Ex 2 M: Name: CH₃–C(CH₃)₂–CH₂–CHO
Solution: Principal FG = –CHO → suffix -al (at C1). Longest chain including CHO = 4C → but. C1=CHO, C2=CH₂, C3=C(CH₃)₂, C4=CH₃. Two methyls at C3 → 3,3-dimethyl. Name: 3,3-dimethylbutanal
Ex 3 H: Name: CH₃–CH=CH–CH(CH₂CH₃)–C(=O)–CH₃
Solution: FGs: C=C (alkene) and C=O (ketone). Priority: ketone > alkene. Suffix: -one. Longest chain including C=O and C=C: 7C if we take the ethyl branch as part of main chain? Count: CH₃–CH=CH–CH(–)–CO–CH₃ = 6C (methyl at end, no — recount). Main chain: CH₃(C6)–CO(C5)–CH(C4)–CH(C3)=CH(C2)–CH₃(C1) = hexan-5-one with C=C at 2. Ethyl substituent at C4. Name: 4-ethylhex-2-en-5-one — check: number from ketone end to give it lower locant.
E Q1. Name: CH₃–CH(CH₃)–CH₂–CH₃
E Q2. Name: CH₃–CH=CH–CH₂–CH₃
E Q3. Draw the structure of 3-methylbut-1-yne.
M Q4. Name: (CH₃)₂CHCH₂CH₂CHO
M Q5. Name: ClCH₂CH(OH)CH₂Br (give correct IUPAC with both halogens and OH).
M Q6. Draw the structure of 2-bromo-4-chloro-3-methylpentane.
H Q7. Name: CH₂=C(CH₃)–CH₂–COOH
H Q8. Name: CH₃–CO–CH₂–CH₂–CH₂–NH₂
| What to do | Rule |
|---|---|
| Find principal FG | Highest priority from FG table → gives SUFFIX |
| Choose parent chain | Longest chain including principal FG + max unsaturation |
| Number the chain | Lowest locant to principal FG → then double bond → then substituents |
| Identical substituents | di, tri, tetra… and separate locants with commas |
| Alphabetize | Only the base names; ignore di/tri/tetra multipliers |
| Format | Numbers–letters (hyphen) | Numbers, Numbers (comma) |