question_answer

                Given                                 In the above compounds correct order of reactivity in electrophilic substitution reactions will be:     JEE Main Online Paper ( Held On 25  April 2013 )

A)                 \[b>a>c>d\]      

B)                                        \[d>c>b>a\]

C)                                        \[a>b>c>d\]      

D)                                        \[b>c>a>d\]

Correct Answer: A

Solution :

                - CF and\[-C{{H}_{3}}\] groups are o and p directing. They are electron releasing due to + E and + M effects. Further since' such groups increase electron density in the nucleus, they facilitate further electrophi-lic substitution and hence known as activating group. The activating effect of these groups is in order of\[-C{{H}_{3}}>-X\] but chlorine exceptionally deactive the ring due -to strong -1 effect. Hence, it is difficult to carry out substitution in chlorobenzene than in benzene. Further \[-N{{O}_{2}}\] is a deactivating group hence deactivates the benzene nucleus, i.e. hinder the further substitution. Thus nitrobenzene undergo electrophilic substitution with a great difficulty hence the correct order will be