JEE Advanced · Chemistry · 24. Haloalkanes & Haloarenes
For the reaction sequence given below, the correct statement(s) is(are)

(In the options, \(X\) is any atom other than carbon and hydrogen, and it is different in \(\mathbf{P}, \mathbf{Q}\) and \(\mathbf{R}\) )
- A C-X bond length in \(\mathbf{P}, \mathbf{Q}\) and \(\mathbf{R}\) follows the order \(\mathbf{Q}>\mathbf{R}>\mathbf{P}\).
- B C-X bond enthalpy in \(\mathbf{P}, \mathbf{Q}\) and \(\mathbf{R}\) follows the order \(\mathbf{R}>\mathbf{P}>\mathbf{Q}\).
- C Relative reactivity toward \(\mathrm{S}_{\mathrm{N}} 2\) reaction in \(\mathbf{P}, \mathbf{Q}\) and \(\mathbf{R}\) follows the order \(\mathbf{P}>\mathbf{R}>\mathbf{Q}\).
- D \(\mathrm{p} K_{\mathrm{a}}\) value of the conjugate acids of the leaving groups in \(\mathbf{P}, \mathbf{Q}\) and \(\mathbf{R}\) follows the order \(\mathbf{R}>\mathbf{Q}>\mathbf{P}\).
Answer & Solution
Correct Answer
(B) C-X bond enthalpy in \(\mathbf{P}, \mathbf{Q}\) and \(\mathbf{R}\) follows the order \(\mathbf{R}>\mathbf{P}>\mathbf{Q}\).
Step-by-step Solution
Detailed explanation

(A) Wrong: bond length order \(\mathrm{Q}>\mathrm{P}>\mathrm{R}\)
(B) Correct: Bond enthalpy \(\mathrm{R}>\mathrm{P}>\mathrm{Q}\)
(C) Wrong: \(\mathrm{S}_{\mathrm{N}} 2\) reactivity \(\quad \mathrm{Q}>\mathrm{P}>\mathrm{R}\)
(D) Wrong: \(\mathrm{pKa}(\mathrm{HI} <\mathrm{HBr} <\mathrm{HF}) \quad \mathrm{R}>\) P \(>\mathrm{Q}(\mathrm{pKa})\)
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