Question

Arrange the following in increasing order of their basic strength.
$C{H}_{3}CO{O}^{\ominus },FC{H}_{2}CO{O}^{\ominus },ClC{H}_{2}CO{O}^{\ominus },BrC{H}_{2}CO{O}^{\ominus }$

• A. $FC{H}_{2}CO{O}^{\ominus }>ClC{H}_{2}CO{O}^{\ominus }>BrC{H}_{2}CO{O}^{\ominus }>C{H}_{3}CO{O}^{\ominus }$
• B. $BrC{H}_{2}CO{O}^{\ominus }>ClC{H}_{2}CO{O}^{\ominus }>FC{H}_{2}CO{O}^{\ominus }>C{H}_{3}CO{O}^{\ominus }$
• C. $ClC{H}_{2}CO{O}^{\ominus }>FC{H}_{2}CO{O}^{\ominus }>BrC{H}_{2}CO{O}^{\ominus }>C{H}_{3}CO{O}^{\ominus }$
• D. $FC{H}_{2}CO{O}^{\ominus }<ClC{H}_{2}CO{O}^{\ominus }<BrC{H}_{2}CO{O}^{\ominus }<C{H}_{3}CO{O}^{\ominus }$

Answer 1

The correct option is D $FC{H}_{2}CO{O}^{\ominus }<ClC{H}_{2}CO{O}^{\ominus }<BrC{H}_{2}CO{O}^{\ominus }<C{H}_{3}CO{O}^{\ominus }$

Convert conjugate base into acid by adding $H^{\oplus }$, find the acidic character and then reverse the order after removing $H^{\oplus }$ ions that would be the order for basic character.

Acidic strength decreases with decrease in strength of -I group thus correct order of -I group is F>Cl>Br>H
Hence, the correct order of basic strength is $FC{H}_{2}CO{O}^{\ominus }<ClC{H}_{2}CO{O}^{\ominus }<BrC{H}_{2}CO{O}^{\ominus }<C{H}_{3}CO{O}^{\ominus }$