See image — Amines Chemistry Question

💡 Solution & Explanation

Concept: De-amination (deamination) of a primary amine with NaNO2/HCl generates a carbocation intermediate via a diazonium ion. The diazonium salt loses N2 to give a carbocation, which can then lose a proton (E1 elimination) or rearrange before elimination. Step 1: Identify the starting material. n-Bu–NH2 is n-butylamine, CH3CH2CH2CH2–NH2 (a straight-chain primary amine). Step 2: Reaction mechanism. Treatment with NaNO2/HCl converts the primary amine to a diazonium salt (RN2+), which is unstable and loses N2 to form the n-butyl carbocation: CH3CH2CH2CH2+. Step 3: Possible products from the n-butyl carbocation. - Direct elimination (loss of H+ from C2): gives 1-butene (CH3CH2CH=CH2). ✓ - 1,2-hydride shift converts n-butyl cation (primary) to sec-butyl cation (CH3CH2+CHCH3), a more stable secondary carbocation. - Elimination from sec-butyl cation: loss of H+ from C1 gives 1-butene; loss of H+ from C3 gives 2-butene. Because the carbocation intermediate is open and the reaction is not stereospecific, both cis-2-butene and trans-2-butene can form. ✓ Step 4: Can isobutene form? Isobutene is (CH3)2C=CH2, which requires a branched carbon skeleton (an isobutyl/tert-butyl framework). To produce isobutene, the carbon skeleton itself would need to rearrange from a straight 4-carbon chain to a branched 4-carbon chain. A simple 1,2-hydride shift from a primary to a secondary carbocation does not create a branched skeleton; a 1,2-methyl shift would be needed to go from the n-butyl skeleton to an isobutyl skeleton, and such a skeletal rearrangement does not occur under these mild carbocation conditions starting from n-butylamine. Therefore, isobutene cannot be obtained. Step 5: Conclusion. 1-butene, cis-2-butene, and trans-2-butene can all be formed, but isobutene (iso-butene) cannot be prepared by de-amination of n-butylamine with NaNO2/HCl. Therefore, the correct answer is D.