MHT CET · Chemistry · Haloalkanes and Haloarenes

What is the order of ease of dehydrohalogenation of alkyl halides?

A \(3^{\circ}\gt2^{\circ}\gt1^{\circ}\)
B \(2^{\circ}\gt1^{\circ}\gt3^{\circ}\)
C \(3^{\circ}\gt1^{\circ}\gt2^{\circ}\)
D \(1^{\circ}\gt2^{\circ}\gt3^{\circ}\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(3^{\circ}\gt2^{\circ}\gt1^{\circ}\)

Step-by-step Solution

Detailed explanation

According to Saytzeff elimination, the ease of dehydrohalogenation depends on the stability of the alkyl substituted alkenes which is given as,
\(\mathrm{R}_2 \mathrm{C}=\mathrm{CR}_2 \gt \mathrm{R}_2 \mathrm{C}=\mathrm{CHR} \gt \mathrm{R}_2 \mathrm{C}=\mathrm{CH}_2,\) \(\mathrm{RCH}=\mathrm{CHR} \gt \mathrm{RCH}=\mathrm{CH}_2\)
\(\therefore \quad\) The ease of \(\alpha, \beta\)-dehydrohalogenation is:
\(3^{\circ} \gt 2^{\circ} \gt 1^{\circ}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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