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IUPAC Nomenclature






IUPAC NAMING Convention
IUPAC (International Union of Pure and Applied Chemistry) is a system of nomenclature where the names are correlated with the structure such that the reader or listener can deduce the structure from the name.
IUPAC Names consists of Prefix-root word - suffix
IUPAC Names for straight chain Alkanes
The names of such compounds is based on their chain structure, and end with suffix ‘-ane’ and carry a prefix indicating the number of carbon atoms present in the chain.

IUPAC Names for Branched Chain Alkanes
Branched Chain Alkanes are the Alkanes which are having branches . Examples are


How to derive the IUPAC Names of Branched Chain Alkanes
1. The longest carbon chain in the molecule is identified. The longest chain of Carbon atom is called the parent or root chain and it decides the root word of the organic compounds. Table is given below for the root words for Carbon atom from 1 to 10

2. Numbering of chain is done in such a way that – substituent gets lowest locant.
3. The names of the alkyl groups attached as a branch are then prefixed to the name of the parent alkane and its position is indicated by numbers.
4. If different alkyl groups are present, they are listed in alphabetical order
5. The names of identical substituents are not repeated, instead prefixes

6. If the two substituents are found in equivalent positions, the lower number is given to the one coming first in the alphabetical listing.
7. The branched alkyl groups can be named by following the above rules only. However, the carbon atom of the branch that attaches to the root alkane is numbered 1
8. If there happens to be two chains of equal size, then that chain is to be selected which contains more number of side chains.
Example -1

Step 1. Longest chain with more side chain is chosen. Since there are 10 C. So, Decane will be root word
Step 2. Branched is name as 2-Ethylbutyl using the same procedure
Step 3. Name is written considering alphabet order of the side chain name
Finally, the Name is
5-(2-Ethylbutyl)-3,3-dimethyldecane
Example -2

Step 1. Longest chain with more side chain is chosen. Since there are 7 C. So, heptane will be root word
Step 2. Now two substituents are found in equivalent positions, the lower number is given to the one coming first in the alphabetical listing
So, it is 3 -ethyl and 5 -methyl
Step 3. Name is written considering alphabet order of the side chain name
3-Ethyl-5-methylheptane

IUPAC Nomenclature for Cyclic Alkanes
A saturated monocyclic compound is named by prefixing ‘cyclo’ to the corresponding straight chain alkane. If side chains are present, then the rules given above are applied.
Example -1

We have 5 carbon .So,it is cyclopentane
Example -2

Here the more branched chain is given lower number
3-ethyl 1-1 dimethyl cyclohexane
IUPAC nomenclature of Functional Groups
1.The longest chain of carbon atoms containing the functional groups is numbered in such a way that the functional group attached to the carbon atom gets the lowest possible number in the chain. The name of the compound is decided by choosing the IUPAC suffix as below

There are few functional group does not have any suffix, so they are treated as substituents only
Class
Structure
IUPAC prefix
Halides
-Cl or -BR or -I
Halo
Ethers
R-O-R
Alkoxy
2. Poly-functional compounds are compounds which are having more than one functional group. For naming poly functional compounds, one of the functional groups is chosen as the principal functional group and the compound is then named on that basis. The remaining functional groups, which are subordinate functional groups, are named as substituents using the appropriate prefixes. The choice of principal functional group is made based on order of preference. The order of decreasing priority for some functional groups is:
-COOH, –SO3H, -COOR (R=alkyl group), COCl, -CONH2 , -CN,-HC=O, >C=O, -OH, -NH2 , >C=C, -C≡C-
Here is the list with suffix and prefix both for poly-functional compound


Examples
A. Carboxylic Acid- R – COOH
R – C – O –O- H
Suffix: - Oic acid (if ‘C’ of COOH is not included in the main chain then Carboxylic acid is used instead of oic acid.)
a. H COOH Meth – 1 oic acid (Formic acid)
b.CH3 – COOH Ethan – 1 oic acid (Acetic acid)
c. CH3 – CH2 – COOH (Propanoic acid)


B. Nitrile- R – C N
Prefix: Cyno
Suffix: nitrile
a.C2 H3 – CN Ethane – 1 – nitril
b.

3 – Methyl butane – 1 – nitrile
c. NC – CH2 – CH2 – COOH
4 – cyno butane – 1 – oic acid
C. Alkenes and Alkynes
CH≡C-CH=CH-CH=CH2
a. The two C=C functional groups are present at carbon atoms 1 and 3, while the C≡C functional group is present at carbon 5.
b. These groups are indicated by suffixes ‘diene’ and ‘yne’ respectively.
c. The longest chain containing the functional groups has 6 carbon atoms; hence the parent hydrocarbon is hexane. The name of compound, therefore, is Hexa-1,3- dien-5-yne
Nomenclature of Substituted Benzene Compounds
Rules
1) In case of substituted Benzene ,the substituent is placed as prefix to the word benzene
2) If benzene ring is disubstituted, the position of substituents is defined by numbering the carbon atoms of the ring such that the substituents are located at the lowest numbers possible
Examples
1.

Here methyl is the substitutent, So IUPAC name is methyl benzene
2.

Here two substituent are present and we take the lowest number.
So,IUPAC name is 1,3 Dibromo benzene

Solved examples

1. Find the IUPAC name
a. HC≡C-CH=CHCH3
b.
c.
Answer
a.pent-3-en-1-yne
b. but-3-en-2-ol
c. 1-Chloro-4-methyl-2-nitrobenzene






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