Naming Of Bigger Compounds

GOC of Class 11

Naming Of Bigger Compounds

Having learnt the names of simple compounds we are now in happy situation to proceed to name the bigger or complex compounds by IUPAC system. There are however more than 70 rules in the system which guide us to name the organic compounds but here we are required to know only six basic rules.

  1. Rule−1: Select the longest continuous carbon chain in a molecule whether it is in straight line (I) or not in straight line (II).
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  3. Rule−2: If the compounds contains one or more longest continuous carbon chains then that chain is accepted which has the largest number of branches.
  4. Let us understand it through an example,
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  6. The above two structural formulae are identical with, difference that if we view it in two ways (I) and (II). Both have the longest chains of 6 carbons atoms, which are numbered. In viewing as (I) we get two branches while viewed as (II) we get one branch.
  7. So, (I) is the correct longest chain.
  8. Rule−3: The rule states that after selecting the longest carbon chain, lowest position number is to be given to the position of substituent say, S. Let us have an example
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  10. In (I) 3 is the lower. Hence (I) is accepted and (II) is rejected. The positional number is also termed as LOCANT which means a number that locates the position of a substituent eg. Locant of S in (I)=3 and locant of S in (II)=5 due to incorrect numbering.
  11. Rule−4: This rule is applicable to those compounds which have more than one substituent(S). In such cases counting is done from that terminal of carbon chain which gives lesser value for the sum of locant values of substituents. Such as
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  13. 2 + 3 + 5 = 10 3 + 5 + 6 = 14
  14. The compounds are identical and after counting we get 7C−atoms. But after counting, the sum of the locants of S should be lowest. Hence (I) is accepted for naming the compound.


IUPAC names of compounds containing poly functional groups

Functional groups Formula Name as substituent Name as parent
Acid −COOH Carboxy Carboxylic or −oic



Sulphonic acid −SO3H Sulpho Sulphonic acid
Ester Naming Of Bigger Compounds Alkoxycarbonyl –oate
Anhydride Naming Of Bigger Compounds  – –oic anhydride
Acid halide −COX Halo carbonyl –oyl halide
Acid amide −CONH2 Carbamoyl or Amido Amide
Cyanide −C ≡ N Cyano Nitrile
Iso cyanide Naming Of Bigger Compounds Iso cyano Iso nitrile or carbyl



Aldehyde −CHO Oxo, aldo (for aldehyde)


Or formyl (for CHO)

Ketone Naming Of Bigger Compounds Oxo or keto –one
Alcohol −OH Hydroxy –ol
Thiol –SH Mercapto Thiol
Amines −NH2 Amino Amine
Ethers −O− Alkoxy
Alkene =  – ene
Alkyne  – yne
Nitro. –NO2 Nitro
Nitroso. –N = O Nitroso
Halogen −X Halo
Alkyl –R Alkyl
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