It is not always easy to predict the position of attack on multiple substituted benzene. If the benzene ring bears different ortho/para directing group at the 1 and 4 position, the position, the position of further substitution is not immediately clear. sometimes steric effect determine the outcome. in other cases, electronic factors determine the outcome, and further reaction will be at the position activated by the more strongly activating group. Some substituents are so strongly activating that no catalyst is needed to restrict the reaction to mono-substitution. It is possible to reduce the activity of such groups (by side chain reaction) so that the reaction can be stopped after mono substitution then and again by a side cahin reaction the original group is restored. effective use can sometimes be made of removable blocking groups on the ring.
Q. Which of the following is the correct major product?
A.
B.
C.
D.
