Naming Of Bigger Compounds

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).
2. 
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,
5. 
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
9. 
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
12. 
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.

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IUPAC names of compounds containing poly functional groups

Functional groups	Formula	Name as substituent	Name as parent
Acid	−COOH	Carboxy	Carboxylic or −oic   acid
Sulphonic acid	−SO3H	Sulpho	Sulphonic acid
Ester		Alkoxycarbonyl	–oate
Anhydride		–	–oic anhydride
Acid halide	−COX	Halo carbonyl	–oyl halide
Acid amide	−CONH2	Carbamoyl or Amido	Amide
Cyanide	−C ≡ N	Cyano	Nitrile
Iso cyanide		Iso cyano	Iso nitrile or carbyl   amine
Aldehyde	−CHO	Oxo, aldo (for aldehyde)   Or formyl (for CHO)	–al
Ketone		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	–