Which of the following reactions DOES NOT involve Hoffmann bromamide degradation?

Solution

Chemistry ma’am · 3 steps

Br₂/NaOH is Hoffmann only when it acts on an amide. In (b) it meets a methyl ketone instead.

1. What Hoffmann needs. Hoffmann bromamide degradation turns a primary amide RCONH₂ into RNH₂ with Br₂ and NaOH. The C=O carbon is lost as carbonate, so the amine has one carbon fewer. Seeing Br₂/NaOH is not enough: check what it is acting on.

   Option	What Br₂/NaOH acts on	Reaction it does	Hoffmann?
   (a)	PhCH₂CONH₂, an amide	amide to PhCH₂NH₂, one C lost	yes
   (b)	PhCH₂COCH₃, a methyl ketone	haloform: gives PhCH₂COOH after H⁺	no
   (c)	PhCONH₂, made from PhCOCl and NH₃	amide to PhNH₂	yes
   (d)	PhCONH₂, made by partial hydrolysis of PhCN	amide to PhNH₂	yes

2. Route in (b). The haloform reaction gives PhCH₂COOH, and heating with NH₃ turns it into the amide PhCH₂CONH₂. Then LiAlH₄ reduces the amide's C=O to CH₂ and keeps every carbon. No amide is ever treated with Br₂/NaOH.
3. So. Option (b) is the only route with no Hoffmann bromamide step. The amine comes from LiAlH₄ reduction of an amide.

The idea to keep. Hoffmann bromamide means an amide treated with Br₂/NaOH, and one carbon is lost. The same reagent on a methyl ketone is the haloform reaction. LiAlH₄ on an amide keeps every carbon.

Answer from the NTA final answer key. Solution by PrepWiser.