Question

The most acidic hydrogen atoms are present in:

• A. Ethane
• B. Ethene
• C. Ethyne
• D. Benzene

Answer 1

The correct option is C

Ethyne

Explanation for correct option:

C. Ethyne

• Ethyne is a chemical compound with a molecular formula ${\mathrm{C}}_2{\mathrm{H}}_2$.
• It is a colorless gas that is used as fuel.
• Ethyne has the highest percentage of s-character than ethane and ethene. Ethyne has $\mathrm{sp}$ hybridized carbon atoms$\left({\mathrm{C}}_2{\mathrm{H}}_2\right)$. Thus the percentage of s-character in ethyne molecule is $50\%$ Hence, the most acidic hydrogen atoms are present in ethyne.
• The greater the s character of the hybrid orbital, the greater the electronegativity of the atom. Such atoms share their electron density and thereby have a greater acidic character.

Explanation for incorrect options:

A. The hybridization of Ethane$\left({\mathrm{C}}_2{\mathrm{H}}_6\right)$ is ${\mathrm{sp}}^3$ and it has $25\%$ s-character.

B. The hybridization of Ethene$\left({\mathrm{C}}_2{\mathrm{H}}_4\right)$ is ${\mathrm{sp}}^2$ and it has $33\%$s-character.

D. The hybridization of benzene$\left({\mathrm{C}}_6{\mathrm{H}}_6\right)$ is ${\mathrm{sp}}^2$ and it has $33\%$s-character.

Hence, the correct option is C i.e. Ethyne.