Q20 / 160 · AP EAMCET 2022 (07 Jul Shift 2) · Chemistry
The decreasing order of acidic nature of the following compounds is
- AIII $>$ II $>$ I
- BII $>$ III $>$ I
- Correct answerCII $>$ III $>$ II
- DI $>$ II $>$ III
Solution
) Terminal alkynes contain $s p \mathrm{C}-\mathrm{H}$ group that is acidic in nature. Acidity also depends on the stability of the conjugate base formed.
$-\mathrm{NO}_2$ is electron withdrawing group and therefore decreases the electron density on the carbanion and thus stabilises the conjugate base. $-\mathrm{NH}_2$ is electron donating group and therefore increases the electron density on the carbanion and thus destabilises the conjugate base. Therefore, the acidity order is II $>$ I $>$ III.
$-\mathrm{NO}_2$ is electron withdrawing group and therefore decreases the electron density on the carbanion and thus stabilises the conjugate base. $-\mathrm{NH}_2$ is electron donating group and therefore increases the electron density on the carbanion and thus destabilises the conjugate base. Therefore, the acidity order is II $>$ I $>$ III.
Hence, the correct answer is option: 'C'.