1. Consider the radical halogenation reaction shown below to answer parts a-c. Note that "Ph" refers to a benzene ring. BDE (kJ/mol) a. Draw the major monobrominated organic product for the reaction. Initiation Br₂, heat Propagation Step 1. Major Organic + HBr Product Step 2. b. Draw an arrow-pushing mechanism that shows the reaction pathway leading to the formation of the major organic product. If multiple stereoisomers are formed, only draw the mechanism for one of them. Bond CH3CH₂-H (CH3)3C-H PhCH₂-H CH3CH₂-Br (H3C)3C-Br PhCH₂-Br Termination (Draw one termination step.) H-Br Br-Br 423 404 378 303 304 264 368 190

Organic Chemistry: A Guided Inquiry
2nd Edition
ISBN:9780618974122
Author:Andrei Straumanis
Publisher:Andrei Straumanis
Chapter15: Radical Reactions
Section: Chapter Questions
Problem 12E
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1. Consider the radical halogenation reaction shown below to answer parts a-c. Note that "Ph"
refers to a benzene ring.
BDE (kJ/mol)
a.
Draw the major monobrominated organic product for
the reaction.
Initiation
Br₂, heat
Propagation
Step 1.
Major
Organic + HBr
Product
Step 2.
Bond
CH3CH₂-H
(CH3)3C-H
PhCH₂-H
b. Draw an arrow-pushing mechanism that shows the reaction pathway leading to the
formation of the major organic product. If multiple stereoisomers are formed, only draw
the mechanism for one of them.
Termination (Draw one termination step.)
CH3CH₂-Br
(H3C)3C-Br
PhCH₂-Br
H-Br
Br-Br
423
404
378
303
304
264
368
190
Transcribed Image Text:1. Consider the radical halogenation reaction shown below to answer parts a-c. Note that "Ph" refers to a benzene ring. BDE (kJ/mol) a. Draw the major monobrominated organic product for the reaction. Initiation Br₂, heat Propagation Step 1. Major Organic + HBr Product Step 2. Bond CH3CH₂-H (CH3)3C-H PhCH₂-H b. Draw an arrow-pushing mechanism that shows the reaction pathway leading to the formation of the major organic product. If multiple stereoisomers are formed, only draw the mechanism for one of them. Termination (Draw one termination step.) CH3CH₂-Br (H3C)3C-Br PhCH₂-Br H-Br Br-Br 423 404 378 303 304 264 368 190
c. Calculate AH° for the first propagation step for this reaction. Show your work and
include units.
d. Calculate AH° for the second propagation step for this reaction. Show your work and
include units.
e. Draw a reaction coordinate diagram for the two-step propagation cycle for the reaction.
Include the two AH values that you calculated previously in the diagram. Label the rate-
determining step. Label each step as exothermic or endothermic.
f. Draw the transition state for the rate-determining step. Does the transition state look most
like the alkane starting material, the radical intermediate, or halogenated product?
Explain your answer. (Hint: Hammond Postulate.)
g. Bromination is 80× more selective for the secondary position than the primary position.
Using this information, complete the chart and determine what percentage of the
experimental product yield will have substitution at each position. Only consider
monobromination products.
Primary
Secondary
Statistical
Experimental Yield
(%)
Selectivity
Transcribed Image Text:c. Calculate AH° for the first propagation step for this reaction. Show your work and include units. d. Calculate AH° for the second propagation step for this reaction. Show your work and include units. e. Draw a reaction coordinate diagram for the two-step propagation cycle for the reaction. Include the two AH values that you calculated previously in the diagram. Label the rate- determining step. Label each step as exothermic or endothermic. f. Draw the transition state for the rate-determining step. Does the transition state look most like the alkane starting material, the radical intermediate, or halogenated product? Explain your answer. (Hint: Hammond Postulate.) g. Bromination is 80× more selective for the secondary position than the primary position. Using this information, complete the chart and determine what percentage of the experimental product yield will have substitution at each position. Only consider monobromination products. Primary Secondary Statistical Experimental Yield (%) Selectivity
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