IUPAC SYSTEM OF NOMENCLATURE OF ORGANIC COMPOUNDS:

IUPAC SYSTEM OF NOMENCLATURE OF ORGANIC COMPOUNDS:

IUPAC SYSTEM OF NOMENCLATURE OF ORGANIC COMPOUNDS:

International Union of pure and applied Chemistry (IUPAC) has suggested a scheme for giving systematic names to organic compounds on the basis of structure. A brief description of this is given here.

Alkanes

1) Nomenclature of Alkanes: The first four members are known by their common names; Methane(CH4), Ethane (C2H6), propane (C3H8) and butane(C4H10).The higher memebers start from Greek prefix that indicate the number of carbon atoms in the molecules and end with "ane" the last three letteers in alkane; pentane (C5H12), hexane (C6H14), heptane (C7H16) and so on. the alkyl group is obtained by removing one hydrogen atom from an alkane; Methyl (CH3), Ethyl (C2H5) , propyl (C3H7) and so on.Some simpler substiuents with branced chains are often given common names isobutyl

CH3CHCH2(-)    , Sec-butyl            CH3CH2CH---    , tert-butyl         ((CH3)3C----).
         |                                                                   |
        CH3                                                                                  CH3

The following rules are followed while naming other alkanes.

a) Longest chain rule: e longest chain of carbon is chosen and the compound is named as a derivative of this alkane.

b) lowest number rule: the numbering of the chain is started from the end where branching gets the lowest number.

c) Preference to the substituent with the least number of carbon atoms: The numbering is started from the end which is nearest to the branch with the least number of carbon atoms.

d) Preference to the greater number substituents: The end of the chainwhich is nearest to the large number of substituents is taken to be thefirst carbon.

e) Alphabetical order of alkyl group: The substituents are named in the alphabetical order irrespective of their placements.The names methyl, dimethyl, trimethyl, etc.are all considered to start with alphabet m.

f) Proper way of writing: A numeral and letter are separated by a hypen, and numeral from numeral by a coma. The entire name is written as one complete word. For example, the name of the compound.

                                                                                      6         7
                                                        CH3                       CH2CH3
                                            1          2|        3        4          5|
                                            CH3---CH---CH---CH2---CHCH3
                                                                  |
                                                              HC---CH3
                                                                                        |
                                                                 CH3 

                                        2,5- dimethyl-3-isopropylheptane
It have 7 carbon atom at longest chain therefore it name is heptane. It also have two methyl (CH3) group at 2 and 5 numbered positioned carbon chain, therefore it got named  as 2,5- dimethyl .It also have  propyl (C3H7) group at 3 numbered positoned carbon chain. So the ultimate name of above organic compound is 2,5- dimethyl-3-isopropylheptane.

Alkenes

2) Nomenclature of Alkenes: The IUPAC name is obtained by replacing the suffix "-ane" of the corresponding alkane by "-ene".The double bond gets the smallest number in the longest carbon chain.More than one double bond is indicated by ending the name with diene, triene, etc.The position of double bond may be placed between the suffix ene and the rest of the name.For example, the name of the compound.

                                  1           2           3           4         5
                                 CH2=CH---CH---CH=CH2
                                                                        |
                                                     CH3
        
                                 3-methyl pent- 1,4 - diene.

Alkynes

 

3) Nomenclature of Alkynes: Here the suffix "-ane" is replaced by "-yne" for example:
 
                                                             CH3
                                                    5       4 |        3          2   _    1
                                                   CH3---CH---CH2---C  =   CH
                                        
                                             4-methylpent - 1 -yne

3D Alcohol Pictures

 

4) Nomenclature of Alcohols: Here the suffix "-ol" replaces "-e" of the alkane to indicate the OH group.For example, the compound.
                                                                                    4             5             6
                                                                                   CH2---CH2---CH3
                                                             1             2           3|
                                                            CH3---CH2---C---OH
                                                                        |
                                                                       CH2CH3
     
                                                        2- ethyl- 3 -hexanol

3-D-Aldehyde

5) Nomenclature of Aldehydes: Here the suffix "-al" replaces the "-e" of the alkane.The numbering of carbon atoms is always done starting from --CHO group.For example, the compound.
                                                                      CH3                O
                                                                       |                    ||
                                                           CH3---CH---CH2---C---H
                                                            4             3           2             1

                                                             3-methylbutanal

Preparation of ketones

 

 


6) Nomenclature of ketones: Here the suffix "-one" is replaced the "-e" of the alkane.For example the compound.

                                                                                     O
                                                               1             2           3||    4
                                                              CH3---CH2---C---CHCH3
                                                                                             |
                                                                                            CH2---CH2---CH3
                                                                                                       5             6             7
                                                          
                                                                4-methyl - 3 -heptanone

3-D-Carboxylic-Acid

 

7) Nomenclature of Carboxylic Acid: Here, the suffix "-oic" acid replaces "-e" of the alkane.The numbering of carbon atoms is always done starting from ---COOH group. For example, the compound.

                                                                                                 CH3           O
                                                                                                  |                ||
                                                               CH3---CH2---CH2---C---CH2---C---OH
                                                                6          5          4        3|      2         1
                                                                                                 CH2CH3

                                                                            3-ethyl- 3-methylhexanoic acid

 

3-D-Amines

8) Nomenclature of amines: Primary amines are named by replacing the ending "-e" of the parent alkane by "-amine". The position of -NH2 is indicated by the number.Secondery and tertiary amines are names as N- substituted derivatives of primary amines. For Example,