Question

# What is the correct order of decreasing stability of the following cations?$$I-\quad CH_3-\overset { * }{ C } H-CH_3$$$$II-\quad CH_3-\overset { * }{ C } H-OCH_3$$$$III-\quad CH_3-\overset { * }{ C } H-CH_2-OCH_3$$

A
II>I>III
B
II>III>I
C
III>I>II
D
I>II>III

Solution

## The correct option is A $$II > I > III$$$$C{H}_{3}-\overset{\ast}{C}H-C{H}_{3} \rightarrow$$ Stable due to +I effect of 2 $$-C{H}_{3}$$ groups.$$C{H}_{3}-\overset{\ast}{C}H-OC{H}_{3} \rightarrow$$ Stable due to strong +R effect of $$-OC{H}_{3}$$ group (lone pair-$$\sigma$$ bond-positive charge).$$C{H}_{3}-\overset{\ast}{C}H-C{H}_{2}-OC{H}_{3} \rightarrow$$ Destabilised by -I effect of $$-OC{H}_{3}$$ group.$$\Rightarrow$$ R effect in $$II$$ dominates I effect in $$I$$Hence, the correct order of stability is $$II > I > III$$.Chemistry

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