Question

a) i) Write ‘Saytzeff rule’.

ii) The products A and B of the following reaction are two isomeric alkenes. Identify Aand B.

b) Identify the main product of the following reactions. Suggest whether the reaction is S_N1 or S_N2.

Answer 1

a) i) The Saytzeff rule states that in dehydrohalogenation reactions, the preferred product is that alkene which has a greater number of alkyl groups attached to the doubly bonded carbon atoms.

b) 

i) (CH₃)₃C−Br \(\overset{aq NaOH}{\longrightarrow}\) (CH₃)₃C−OH 

This reaction follows S_N1 mechanism. Tertiary alkyl halides undergo S_N1 reaction very fast because of the high stability of 3° carbocations.

ii) C₆H₅CH₂Br⟶C₆H₅CH₂OH

This reaction follows S_N1 mechanism. Ben- zylic halides show high reactivity towards the S_N1 reaction because the benzylic carbocation formed is stabilised through resonance.