IUPAC NOMENCLATURE
CLASS 10 SCIENCE | CARBON AND ITS COMPOUNDS | BOARD EXAM REVISION
CORE DEFINITION
IUPAC nomenclature is a systematic method of naming organic compounds using the carbon chain, bonds,
functional groups and substituents.
1. THE 4-STEP NAMING ROUTINE
Step Identify Ask yourself
1 Carbon chain How many carbon atoms are in the parent chain?
2 Bond type Are the C–C bonds single, double or triple?
3 Functional group / branches Is there –OH, –CHO, >C=O, –COOH, a halogen or a carbon branch?
4 Numbering Which direction gives the lowest appropriate locants under the naming rules?
2. TYPES OF HYDROCARBONS
Hydrocarbons contain only carbon (C) and hydrogen (H).
Type Bond General formula* Suffix Example
Alkane Single (C–C) CₙH₂ₙ₊₂ -ane Ethane
Alkene Double (C=C) CₙH₂ₙ -ene Ethene
Alkyne Triple (C≡C) CₙH₂ₙ₋₂ -yne Ethyne
*For open-chain hydrocarbons with one type of unsaturation.
MEMORY TRICK
Alkane: +2 → Alkene: no extra 2 → Alkyne: −2 (relative to 2n).
IUPAC Nomenclature • Revision Notes • 1
, 3. CARBON PREFIXES
No. of C atoms Prefix Alkane example
1 Meth- Methane
2 Eth- Ethane
3 Prop- Propane
4 But- Butane
5 Pent- Pentane
6 Hex- Hexane
7 Hept- Heptane
8 Oct- Octane
9 Non- Nonane
10 Dec- Decane
4. FUNCTIONAL GROUP QUICK IDENTIFICATION
Functional group Recognition Naming clue Example
Halogen –Cl, –Br, –I Chloro-, bromo-, iodo- Chloroethane
Alcohol –OH -ol Ethanol
Aldehyde –CHO -al Propanal
Ketone >C=O within chain -one Propanone
Carboxylic acid –COOH -oic acid Ethanoic acid
5. HALOGEN COMPOUNDS
Use chloro-, bromo- or iodo- for chlorine, bromine or iodine attached to the carbon chain.
Structure Reasoning IUPAC name
CH₃–CH₂–Cl 2 carbons; Cl substituent Chloroethane
CH₃–CH(Cl)–CH₃ 3 carbons; Cl on C-2 2-Chloropropane
CH₂Cl–CHCl–CH₃ Cl groups on C-1 and C-2 1,2-Dichloropropane
CH₃–CH(Br)–CH₂–Cl Alphabetical substituent order; lowest locants 2-Bromo-1-chloropropane
REPEATED GROUPS & ALPHABETICAL ORDER
Two identical groups: di-; three: tri-; four: tetra-. Different substituents are written alphabetically (e.g., bromo
before chloro). Alphabetical order does not override numbering rules.
IUPAC Nomenclature • Revision Notes • 2
CLASS 10 SCIENCE | CARBON AND ITS COMPOUNDS | BOARD EXAM REVISION
CORE DEFINITION
IUPAC nomenclature is a systematic method of naming organic compounds using the carbon chain, bonds,
functional groups and substituents.
1. THE 4-STEP NAMING ROUTINE
Step Identify Ask yourself
1 Carbon chain How many carbon atoms are in the parent chain?
2 Bond type Are the C–C bonds single, double or triple?
3 Functional group / branches Is there –OH, –CHO, >C=O, –COOH, a halogen or a carbon branch?
4 Numbering Which direction gives the lowest appropriate locants under the naming rules?
2. TYPES OF HYDROCARBONS
Hydrocarbons contain only carbon (C) and hydrogen (H).
Type Bond General formula* Suffix Example
Alkane Single (C–C) CₙH₂ₙ₊₂ -ane Ethane
Alkene Double (C=C) CₙH₂ₙ -ene Ethene
Alkyne Triple (C≡C) CₙH₂ₙ₋₂ -yne Ethyne
*For open-chain hydrocarbons with one type of unsaturation.
MEMORY TRICK
Alkane: +2 → Alkene: no extra 2 → Alkyne: −2 (relative to 2n).
IUPAC Nomenclature • Revision Notes • 1
, 3. CARBON PREFIXES
No. of C atoms Prefix Alkane example
1 Meth- Methane
2 Eth- Ethane
3 Prop- Propane
4 But- Butane
5 Pent- Pentane
6 Hex- Hexane
7 Hept- Heptane
8 Oct- Octane
9 Non- Nonane
10 Dec- Decane
4. FUNCTIONAL GROUP QUICK IDENTIFICATION
Functional group Recognition Naming clue Example
Halogen –Cl, –Br, –I Chloro-, bromo-, iodo- Chloroethane
Alcohol –OH -ol Ethanol
Aldehyde –CHO -al Propanal
Ketone >C=O within chain -one Propanone
Carboxylic acid –COOH -oic acid Ethanoic acid
5. HALOGEN COMPOUNDS
Use chloro-, bromo- or iodo- for chlorine, bromine or iodine attached to the carbon chain.
Structure Reasoning IUPAC name
CH₃–CH₂–Cl 2 carbons; Cl substituent Chloroethane
CH₃–CH(Cl)–CH₃ 3 carbons; Cl on C-2 2-Chloropropane
CH₂Cl–CHCl–CH₃ Cl groups on C-1 and C-2 1,2-Dichloropropane
CH₃–CH(Br)–CH₂–Cl Alphabetical substituent order; lowest locants 2-Bromo-1-chloropropane
REPEATED GROUPS & ALPHABETICAL ORDER
Two identical groups: di-; three: tri-; four: tetra-. Different substituents are written alphabetically (e.g., bromo
before chloro). Alphabetical order does not override numbering rules.
IUPAC Nomenclature • Revision Notes • 2
