Q43P a. Explain why 1-bromo-2,2-dimet... [FREE SOLUTION]

Chapter 9: Q43P (page 433)

a. Explain why 1-bromo-2,2-dimethylpropane has difficulty undergoing both SN² and SN¹ reactions.
b. Can it undergo E2 and E1 reactions?

Short Answer

Expert verified

a) 1-bromo-2,2-dimethylpropane doesn鈥檛 undergo elimination reaction as C-Br and C-H bonds are not in anti-periplanar position.

b) It can鈥檛 undergo E2 and E1 reaction as it doesn鈥檛 have an 饾湺 H to undergo elimination with C-Br bond.

Step by step solution

Definition of SN1 reaction

SN¹ reaction is a nucleophilic substitution reaction which form carbocation in 1^st step before the breaking of C-halogen bond. It shows a carbocation like transition state.

A reaction mechanism with an experimental compound is given below.

Definition of SN2 reaction

SN² reaction is a nucleophilic substitution reaction where the Nucleophilic attack and bond breaking between carbon and electronegative group happens simultaneously through a 5 coordinated transition state. In this reaction, the rate equation is second order having both the concentration of nucleophile and alkyl bromide.

A reaction mechanism with an experimental compound is given below,

Reason of difficulty in reaction mechanism

a) The given compound is a primary bromide and forms primary carbocation when C- Br bond breaks.

Now, we know as in SN² reaction, back side attack happens, carbocation reactivity increases with decreasing steric hindrance. Though this compound is primary carbocation, the bulky groups attached to it makes difficulties to undergo SN² reaction.

In case of SN¹ reaction, carbocation stability determines the reaction mechanism and tertiary carbocation shows highest reactivity as it is the most stable carbocation. But here in this case, the carbocation is primary. So, it is not as stable as it should be to undergo SN¹ reaction with an ease.

probability of elimination reaction

To undergo elimination reaction, there should an H in the 饾湺 position of C-Br bond. In this case, the compound doesn鈥檛 have an 饾湺 H for which it doesn鈥檛 undergo any of elimination (E1, E2) reaction.