Question

The decreasing basic character of the following is:
I. $Ph{O}^{\ominus }$ II. $C{H}_3{S}^{\ominus }$ III. $\stackrel{\ominus }{O}H$ IV. $Me{O}^{\ominus }$

• A. I > II > III > IV
• B. III > IV > II > I
• C. IV > III > II > I
• D. I > II > IV > III

Answer 1

The correct option is B III > IV > II > I

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.

$Ph{O}^{\ominus }$ is most stable because the negative charge on oxygen is stabilised by resonance. In between $C{H}_3{S}^{\ominus }$ and $Me{O}^{\ominus }$ size od S is greater than O. So, $C{H}_3{S}^{\ominus }$ is more stable than $Me{O}^{\ominus }$. $O{H}^{\ominus }$ is the least stable among all.

Acidity : $PhOH>C{H}_{3}SH>MeOH>H_{2}O$

Basicity: $Ph{O}^{\ominus }<C{H}_3{S}^{\ominus }<Me{O}^{\ominus }<O{H}^{\ominus }$
(Hence the answer is b.)