question_answer

Reactivity of \[PhMgBr\]with the following in the decreasing order is

(I) \[PhCHO\]

(II)

(III)

(IV)

A) I > IV > II > III

B) III > II > IV > I

C) I > III > II > V

D) I > III > II > IV

Correct Answer: A

Solution :

[a] EDG (Me group) at \[o-,\] \[m-,\] and p-positions: At ortho-position, ED power of \[(Me-)\] group is more than p and m (due to \[+1\] effect and hyperconjugation effect). ED power of \[(Me-)\] group at ortho-position is slightly less than the \[Me\]groups at ortho-position (due to less \[+I\]effect, but equal hyperconjugative effect). So the order of ED power of \[(Me-)\] group is \[o>p>m-.\]NA is favoured by less-substituted EDG or more-substituted EDG or more-substituted EWG. So, the order of reactivity of \[PhMgBr\]with aromatic aldehyde is