Answer
a) 1-chloro-2-fluorobenzene
b) 1-ethyl-4-fluorobenzene
c) 1,4-Diiodobenzene
Work Step by Step
General form for naming disubstituted benzene:
write 1st substituent name, then 2nd substituent name and add suffix 'benzene'.
But we have to assign number before each substituent's name to describe their location in benzene ring. When two substitutes are present in the benzene ring then the location of those substitutes in the benzene ring can be done by numbering the benzene ring from 1 to 6. Main substitute (alphabetically first) will always attached to no. 1 carbon and the next substituent can be at position 2,3 or 4.
In problem a., two substitutes are Chlorine and fluorine. So, Chlorine will get the first preference (alphabetically first). Similarly in problem b, ethyl group is attached to first carbon of benzene ring and fluorine on 4th position.
If same substitute is present twice in benzene ring, then the general form for naming disubstituted benzene is:
write the assigned numbers given to ring Carbon atoms to which the substituents are attached. Then add 'di' before substituent name and add suffix 'benzene'. See solution to the last problem.
