ICQs 4 - radical reactions practice PDF

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radical reactions practice
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Hendrix–Chem 230, Fall 2019 RADICAL REVIEW SHEET (+ some synthesis) 1. Determine the most stable radical site on a molecule. 2. Draw the mechanism for radical halogenation. 3. Use BDEs to determine: (1) overall exothermicity or endothermicity of reaction, and (2) ∆H of individual steps. 4. Use experimental results to determine selectivity of radical halogenation. 5. Use Hammond postulate to explain selectivity. 6. Draw early and late transition states. 7. Predict the major product(s) of allylic (and benzylic) halogenation. 8. Use radical bromination in a synthesis. 9. Know the mechanism for anti-Markovnikov addition of HBr to alkene. 10. Know radical polymerization (compare with cationic polymerization). 11. Basic understanding of ozone depletion, biological radical traps. Sample Problems: 1. Determine the most stable site for a radical in the following compounds:

2. A. Show the mechanism for radical chlorination of butane to form 1-chlorobutane.

B. Using the following table of BDEs, determine ∆H for the relevant chain propagation steps.

C. Is the reaction overall exo- or endothermic? D. Is the rate-determining step (rds) exo- or endothermic?

Hendrix–Chem 230, Fall 2019

E. Draw the transition state for the rds. Is it an early or late transition state?

F. Draw a potential energy diagram for the rds.

G. Superimpose on the energy diagram above the energetics of the rds for formation of 2-chlorobutane. H. If 2-chlorobutane is formed in 75% yield and 1-chlorobutane is formed in 25% yield, what is the relative selectivity of chlorination for 2° vs. 1° radical formation? Show your work.

3. A. Draw all possible products of radical bromination of 1-phenyl-2-tbutylcyclohexene:

B. Determine which of these products is most likely to be the dominant one and use pictures to explain why.

Hendrix–Chem 230, Fall 2019 4. Predict the major product(s) of the following:

5. A student runs the following radical bromination below. However, when she takes the IR of the major product, it is clear that there are no C–H stretches due to the presence of a double bond (remember the 3000 cm –1 divide rule!). Suggest a likely product.

6. Synthesize each molecule from cyclohexanol and any other alcohols containing 4 or fewer carbons, and any necessary reagents....