Ncert Exercises & Solutions

The correct order of decreasing stability of the following cations is:

I	\( ~~~~~~~~~~~~\oplus\\ CH_3 - CH-CH_3\)
II	\( ~~~~~~~~~~~~\oplus\\ CH_3 - CH-OCH_3\)
III	\( ~~~~~~~~~~~~\oplus\\ CH_3 - CH-CH_2- OCH_3\)

1.	II>I>III	2.	I>II>III
3.	II<I<III	4.	I<II<III

Hint: Electron donating group stabilizes the carbocation.

The stability of given cations can be understood by the following structures.

The second carbocation is stabilized by the mesomeric effect of oxygen. The first carbocation is stabilized by the inductive effect of two methyl groups. The third carbocation is destabilized by the -I effect of the oxygen atom.

Hence, the decreasing order of stability of carbocation is

II > I > III

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