question_answer

The descending order of stability, of the carbonium ions \[{{C}_{6}}{{H}_{5}}\overset{+}{\mathop{C}}\,{{H}_{2}}(I),p(C{{H}_{3}}O){{C}_{6}}{{H}_{4}}\overset{+}{\mathop{C}}\,{{H}_{2}}(II),p(N{{O}_{2}})\] \[{{C}_{6}}{{H}_{4}}\overset{+}{\mathop{C}}\,{{H}_{2}}(III)\]and \[p(C{{H}_{3}}){{C}_{6}}{{H}_{4}}\overset{+}{\mathop{C}}\,{{H}_{2}}(IV)\]

A)  \[IV>II>I>III\]

B)  \[II>IV>m>l\]

C)  \[II>IV>I>III\]

D)  \[IV>II>III>I\text{ }\]

Correct Answer: C

Solution :

 In the presence of electron releasing group, (like\[C{{H}_{3}},C{{H}_{3}}O\]), the positive charge is dispersed more. This dispersal of positive charge     stabilises     the     carbocation (carbonium ion). While electron withdrawing substituent (like\[\text{N}{{\text{O}}_{\text{2}}}\]) destabilises the carbonium ion by intensifying the positive charge. Thus, the order of stability of given benzyl carbonium ions is as