Solution Found!
The light-initiated reaction of 2,3-dimethylbut-2-ene with
Chapter 8, Problem 9P(choose chapter or problem)
The light-initiated reaction of \(2,3 \text {-dimethylbut }-2-\text { ene }\) with
\(\mathrm{N}-\text { bromosuccinimide }(\mathrm{NBS})\) gives two products:
Give a mechanism for this reaction, showing how the two products arise as a conse- quence of the resonance-stabilized intermediate.The bromination of cyclohexene using NBS gives only one major product, as shown on page 227. Explain why there is no second product from an allylic shift.
Equation Transcription:
Text Transcription:
2,3-dimethylbut-2-ene
N-bromosuccinimide (NBS)
H3C
CH3
H3C
CH3
NBS,hv
H3C
H3C
CH3
CH2-Br
Br
C
CH3
CH3
C
CH2
CH3
Questions & Answers
QUESTION:
The light-initiated reaction of \(2,3 \text {-dimethylbut }-2-\text { ene }\) with
\(\mathrm{N}-\text { bromosuccinimide }(\mathrm{NBS})\) gives two products:
Give a mechanism for this reaction, showing how the two products arise as a conse- quence of the resonance-stabilized intermediate.The bromination of cyclohexene using NBS gives only one major product, as shown on page 227. Explain why there is no second product from an allylic shift.
Equation Transcription:
Text Transcription:
2,3-dimethylbut-2-ene
N-bromosuccinimide (NBS)
H3C
CH3
H3C
CH3
NBS,hv
H3C
H3C
CH3
CH2-Br
Br
C
CH3
CH3
C
CH2
CH3
ANSWER:
Solution 9P :
Step 1:
Given reaction :
The light-initiated reaction of 2,3-dimethylbut-2-ene with N-bromosuccinimide (NBS) gives two products:
(a) Give a mechanism for this reaction, showing how the two products arise as a consequence of the resonance-stabilized intermediate:
The propagation mechanism of the reaction is as shown below :
NBS produces low concentrations of Br2, so the mechanism shown here uses Br2 as the source of bromine, even though it originally came from NBS.
The resonance-stabilized allylic radical intermediate has radical character on both the 1o and 3o carbons, so bromine can bond to either of these carbons producing two isomeric products.