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Chapter 10: Radical Reactions What's Covered? Heterolytic vs homolytic bond breaking/forming Radical stability Halogenation of alkanes mechanism with Brz or CI2 Regioselectivity and Stereochemistry
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Vidlo lectune Notes.
VS.
Stability of Radicals Stability: ARI0 Inductive: Resonance: Increasing stability R
ote
Tertiary
Methy
Primary
UMstuble Arrow Types: Double-barbed arrow
Single-barbed arrow
shows the motion of two electrons
shows the molion of one electron
Resonance Example:
y
L
Patterns in Radical Mechanisms
fM
1.Initiation:Homolytic Cleavage: initiated by light or heat Away W/i'euch othex elr orhv 2. Propagation 1302 Hydrogen abstraction: not the same as proton transfer [R) Nec RadiCaJ X-FH
Halogen abstraction
R
R-
3.
Pordhet >X-X
Termination
Chlorination of Methane Cl2 CH4 CHgCI hv Methane Methyl chloride
HCI
Step1:Initiation:homolytic cleavage :!?0 oD: G i3JID Step2Propagation a) Hydrogen Abstraction: H3CH Ci: : -)HcH-Ci b)Halogen Abstraction 113-:5-0F:1H Step3:Termination Poodhct
: ) :ci-ci:
a
RADICAL MECHANISMS! Other Coupling Possibilities: Rate AC-CH3 HC=C1
Polychlorination:
CI
CI
H H-C-
CIz H-C-CI hv H
Cl2
CI, H- CI CI- CI CI Methylene Chloroform Carbon chloride tetrachloride C1 -c-cs HC-CI C1 el
H
H
Methyl chloride
HaC
Radical Thermodynamics and Regioselectivity sfas 8 CI2
~100%
-0% Mind8
701.mG Majox A
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