Question

help with #1 & #2 Please

1. Show the major product of the following reactions. 1 eq. HBr 1 eq. HBr -15°C 50°C U 1 eq. HBr 50°C 1 eq. HBr -15°C 1 eq. HBr 50°C 1 eq. HBr -15°C 2. Provide a curved arrow mechanism that can account for the formation of both products.

Answer 1

1. The given reaction is an electrophilic addition reaction of HBr on alkene. Two different reaction conditions give two different products. At higher temperature, thermodynamically controlled product is formed in which 1,4-addition product is formed. At lower temperature, kinetically controlled product is formed in which 1,2-addition product is formed. The reactions are shown as follows: H. Br ;Br: :Br: -15°C Kinetically controlled product (1,2-addition product) Br 50°C :Br: Thermodynamically controlled product (1,4-addition product) The reactions are shown as follows: Br Br -15°C Kinetically controlled product (1.2-addition product)

Br 50°C 13 :Br Thermodynamically controlled product (1,4-addition product) Reactions are shown as follows: :Br: -15°C -Br Kinetically controlled product (1,2-addition product) :Br: 50°C -Br :Br -Br: Thermodynamically controlled product (1,4-addition product) 2. In the given there are two possible products for which the mechanism is shown as follows: In the first, pi electrons would abstract a proton from the HBr molecule forming a carbocation shown as follows:

H. Br: There are two possible pathways from this step that could lead to two different products shown as follows: In this step, carbocation rearrangement does not take place and bromide ion attacks the carbocation forming an addition product. Br :Br: (1.2-addition product) Another possible pathway is that carbocation rearrangement takes place and after that bromide ion attacks the electrophilic carbon forming another addition product. :Br Br (1.4-addition product)