JEE Chemistry 2024 Question with Solution

Given: We need the ascending acidity order of the labeled hydrogen atoms A, B, C, and D.

Find: The correct increasing order of acidity.

Acidity depends on the stability of the conjugate base formed after removal of the hydrogen atom. A more stable conjugate base corresponds to a stronger acid.

From the solution:

1. In A, the hydrogen is attached to an $sp$-hybridized carbon. Its conjugate base is most stabilized because of the highest $s$-character.
2. In B, the hydrogen is attached to an $sp^2$-hybridized carbon. Its conjugate base is less stable than that from A, but more stable than those from $sp^3$ carbons.
3. In C, the hydrogen is attached to an $sp^3$-hybridized carbon, so its conjugate base is least stabilized.
4. In D, the hydrogen is also associated with an $sp^3$-hybridized carbon, but its surrounding groups provide slightly better stabilization than C.

Therefore, the acidity increases as:

$$C < D < B < A$$

Hence, the correct option is A.

Given: The compounds corresponding to A, B, C, and D are compared through the stability of their conjugate bases.

Find: The ascending order of acidity.

The solution states that acidity strength is governed by conjugate base stability. Greater conjugate base stability means greater acidity.

The comparative stability shown is:

$$\text{CH} \equiv \text{C}^- > \text{CH}_2 = \text{CH}^- > \text{H}_3\text{C} - \text{CH}_2^- > (\text{CH}_3)_3\text{C}^-$$

This corresponds to the trend:

• $sp$ carbanion is most stable
• $sp^2$ carbanion is next
• less substituted $sp^3$ carbanion is more stable than the more substituted one

So the acidity order becomes:

$$C < D < B < A$$

Thus, the ascending order of acidity is C < D < B < A, and the correct option is A.