Chemistry - GOC Question with Solution | TestHub
Use arrow pushing to explain the following reactions (heterolytic-type reaction mechanisms). The total number of curved arrows needed to show the mechanisms of (a), (b) and (c) together is :
(a) 
(b) 
(c) 
Options:
Answer:
Solution:
(a) SN2: CH3S- attacks the carbon from the side opposite Br while the C-Br pair leaves with Br-. This involves 2 arrows. Arrow pushing is illustrated below:
(b) Claisen rearrangement is a concerted [3,3] shift described by three electron-pair arrows in a cycle. The C=C bond of the vinyl group forms the new C-C bond, the allylic C=C pair shifts to form the new C=C bond, and the O-CH2 pair becomes the C=O bond. This involves 3 arrows. Arrow pushing is illustrated below:
(c) Cation-π cyclization: The alkene π bond attacks the tertiary carbocation (resulting in a 6-membered ring closure), which involves 1 arrow, giving the tertiary 1,1,3-trimethylcyclohexyl cation. The total number of arrows is 2 + 3 + 1 = 6, so the answer is (B).
