Question

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Question :-
Write the rules for writing IUPAC names.

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Answer 1

• To write the name of an organic compound in accordance with IUPAC system, firstly we have to identify the parent hydrocarbon or alkane and the functional groups attached to it.
• After that, the name of the parent hydrocarbon is modified by using suitable prefixes and suffixes to get the actual name of the compound.

1. Nomenclature of straight chain hydrocarbons or parent hydrocarbon - to write the name of straight chain hydrocarbon first we have to to write the word root or prefix that indicates the number of carbon atoms present in that chain. after writing the word root or prefix we add suffix 'ane' to it to get the name of the hydrocarbon.
2. Naming alkyl group - the group obtained by removing one hydrogen atom from the saturated hydrocarbon or alkane is called the alkyl group. these groups are named by replacing 'ane' of alkane by 'yl'.

Answer 2

IUPAC System of Nomenclature of Complex Compounds

The naming of any organic compound depends on the name of normal parent hydrocarbon from which it has been derived. IUPAC system has framed the set of rules for various types of organic compounds.

[ Functional group > Double Bond > Triple bond > Substituent ]

Rules for naming complex aliphatic compounds with no functional group is present (saturated hydrocarbon or paraffins or alkanes) :

• Longest chain rule : The first step in naming an organic compound is to select the longest continuous chain of carbon atoms which may or may not be horizontal. This continuous chain is called parent chain or main chain and other carbon change attached to it are known as side chain or substituents.

• Position of the substituent : Number of the carbon atoms in the parent chain as 1,2,3, etc. starting from the end which gives lower number to the carbon atoms carrying the substituents. The number that indicates the position of the substituent or side chain is called locant.

• Lowest set of locants : When two or more substituents are present, then end of the parent chain which gives till lowest set of locants is preferred for numbering. This rule is called lowest set of locants. This means that when two or more different sets of locants are possible, that set of locants which when compared term by term with other sets each in order of increasing magnitude, has the lowest term at the first point of difference. This rule is used irrespective of the nature of the substituent.

More information :

1. The formal system of nomenclature used today is one proposed by the International Union of Pure and Applied Chemistry (IUPAC). This system was developed in 1892 and has been revised at regular intervals to keep it up to date. Underlying the IUPAC system of nomenclature for organic compound is a fundamental principle.

Any given organic structure has only one IUPAC name and any given IUPAC name represents only one molecular structure.

The IUPAC name of any organic compound essentially consists of three parts :

a. Word root

b. Suffix

c. Prefix

2. According to NCERT, a systematic name of an organic compound is generally derived by identifying the parent hydrocarbon and the functional group (s) attached to it. By further using prefixes and suffixes the parent name can be modified to obtain the actual name. Compounds containing carbon and hydrogen only are called hydrocarbons. A hydrocarbon is termed saturated if it contains only carbon carbon single bonds. The IUPAC names for a homologous series of such compounds is alkane. Paraffin was the earlier name given to these compounds. Unsaturated hydrocarbons are those which contain at least one carbon carbon double or triple bond.

Nomenclature of branched chain alkanes :

• The longest carbon chain in the molecule is to be identified.

• The numbering is done in such a way that the branched carbon atoms get the lowest possible number.

• The lowest number is given to the one coming first in the alphabetical listing.

• The carbon atoms of the branch that attaches to the root alkane is numbered one.

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