Question

3. Do primary alcohols undergo rearrangement upon conversion to the alkyl halide? Explain why or why not. Draw a mechanism or intermediates to help explain.

Answer 1

Primary alcohols do not undergo rearrangement upon conversion to alkyl halides as primary alcohols follow Sn2 during conversion to alkyl halides. During this, it undergoes protonation and a water molecule can go out only if there is an attack from the halide ion. The carbocation rearrangement takes place only when there is a Sn1 reaction that is underway and carbocation formation is there. In Sn2, there is no such formation of a carbocationic intermediate. so, no rearrangement is there.

Though there is an exception to the above generalization. it comes to existence when the alcohol is of following structure-

བ། ་ HX @ ? ༤ དང་པོ་ ༧ 2 CH3OHT Xo Hao Pdt

It undergoes bromination via carbocation rearrangement(and obviously via Sn1!)-

c-CH2-OH CH3 Neoperty alcoho?

Les protagoniste et (050) C-ute et H HX . Ota Neopentyl alcohol (HC) c- Oddz | 1,2-Me shift ( CH3 a cm ty eltza 3 até jo c- cha-ch3 CH more stable t-amy! çation dointermediate - t-amyl halide