Lowest Number rule : The Carbon compound which contains only one substituent number the Carbon atom in such a way that the carbon atom carrying the substituent get the lowest number.

5 4 3 2 1 CH3 -- CH -- CH2 -- CH2 -- CH3 CH3 (Incorrect method) 1 2 3 4 5 CH3 -- CH -- CH2 -- CH2 -- CH3 CH3 (Correct method)

Lowest Sum rule : If there are two or more substituents in the carbon compounds the parent chain is numbered from the end which gives the lowest sum of more substituent carbon.

H3 1 2 3 4 5 6 CH3 -- CH -- CH2 -- CH2 -- C -- CH3 CH3 CH3 6 5 4 3 2 1 CH3 -- CH -- CH2 -- CH2 -- C -- CH3 CH (2+5+5 = 12 Incorrect method) (2+2+5 = 9 Correct method)

Alphabetical Order : When two or more different groups are present, such groups are arranged in alphabetical order.

Observe the names of the following compounds. Divide the given name as per the notations given above and identify the parts in the name through the numbers given above from (1) to (11) and write them in your note book. Take the help of your teacher

❖ CH3 –CH2 –CH2 –CH3 : Butane 4 3 2 1
❖ CH3 –CH2 –CH=CH2 : But-1-ene 1 2 3 4
❖ CH3 –CH–CH2 –CH3 : 2-Chloro butane | Cl 1 2 3 4
❖ CH3 –CH–CH–CH3 : 2, 3 – dichloro butane | | Cl Cl
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