CH3BrCH3FCH3OHCH3OSO2CF3 (I)(II)(III)(IV) The correct order of decreasing reactivity of the above compounds towards CH3O− in an SN2 reaction is :
A
I>IV>II>III
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B
IV>I>II>III
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C
IV>I>III>II
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D
IV>II>I>III
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Solution
The correct option is BIV>I>II>III The correct order of decreasing reactivity of the above compounds towards CH3O− in an SN2 reaction is IV>I>II>III
or CH3OSO2CF3>CH3Br>CH3F>CH3OH
−OSO2CF3 is the best leaving group as the negative charge on O is stabilized by resonance with other O atoms attached to S and due to electron-withdrawing (−I) effect of trifluoromethyl group. Hence, the reactivity of IV is maximum.
The reactivity of III is minimum because hydroxide ion is a poor leaving group and there is no stabilization for the negative charge on O atom.
Also, the stability of Br− is more compared to F− which indicates more reactivity of CH3Br over CH3F.