Question 1: Place the following compounds in order of increasing C-Cl bond strength?

(a) H₃C-Cl
(b) Ph-Cl
(c) PhCH₂-Cl
 

Question 2: What is the weakest bond in the following compounds?

(a) BrCCl ₃
(b) Ph₃CH
(c) CH₃CH(OH)CH₃
(d) CH₃CO₂H
(e) PhCHO
 

Question 3: Why can the 2,4,6-tri-tert-butylphenyl radical be observed using EPR (or ESR) spectroscopy and yet the phenyl radical cannot?

Question 4: What radicals are formed on photolysis or thermolysis of the following compounds?

(a) Bu₆Sn₂
(b) ^tBuOOH
(c) (CH₃)₂C(CN)N=NC(CH₃)₂ CN
(d) (PhCO₂)₂
(e) RONO
(f) ROCl
 

Question 5: What radicals are formed from the following reactions?  Do these reactions involve oxidation or reduction of the organic starting material?

(a) PhI + SmI₂
(b) CH₃COCH₂CO₂CH₃ + Mn(OAc)₃
(c) CH₃CH₂CO₂H + (H₄N)₂ Ce(NO₃)₆
(d) (PhCO₂)₂ + FeCl₂

Question 6: Classify the following radicals as of nucleophilic or electrophilic type.

(a) ^.Cl
(b) ^.CH₂CH₃
(c) ^.CH₂OCH₃
(d) ^.CH₂CO₂CH₃
 

Question 7: Classify the following as either radical abstraction, addition or fragmentation reactions.

(a) EtCO₂^.   →   Et^.   + CO₂
(b) ^tBuO^.   +  Bu₃Sn-SnBu₃ → ^tBuO-SnBu₃   +  ^.SnBu₃
(c) Bu₃Sn^.   +  S=CR₂ →   Bu₃Sn-S-^.CR₂
(d) ^tBuCO^. →   Me^.   + Me₂CO
(e) Cl^.    + HCCCH₃ →   Cl-CH=C^.CH₃
 

Question 8:   Radicals at the α -position of epoxides (see below) can fragment in one of two ways.  How does the R substituent influence the fragmentation pathway?

Question 9: For methyl ethanoate (below), the C-H_A and C-H_B bond strengths are approximately the same.  Why does the ethyl radical prefer to abstract an H_A atom while a methoxyl radical selectively abstracts an H_B atom?

Question 10: The relative rates of reaction of the tert-butoxyl radical (^tBuO^.) with cyclohexane, tetrahydrofuran and 2-propanol are 1 : 5 : 113, respectively.

(a) Draw the structure of the radicals which are formed from each of the three reactions.
(b) Provide an explanation for the different reaction rates.

Question 11: The relative rates of reaction of the cyclohexyl radical (C₆H₁₁^.) with 1-hexene and methyl methacrylate (CH₂=CHCO₂CH₃) are typically 1:3000, respectively.

(a) Provide an explanation for the different reaction rates.
(b) Draw the structure of the predominant radical which is formed in each of the two reactions and account for the regioselectivity in each case.

© Department of Chemistry, University of York.