Ove up antibonding thetwo e cts on thep orbital

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Unformatted text preview: bital to m up. ove up antibonding Thetwo e cts on thep orbital cancel ffe The cancel e othe out; thetwo π orbitals are ach r pushe apart: “e rgy splitting”; d ne im portantly, theπ bonding orbital goes down. down Ethe ne π* π* 0 up Nonbondin g MO 2) p E π unchange d 3) π down Allyl p Orbital Allylic radical is stabilize by 13.5 kcal m -1. d ol Re sulting picture : # of e de nds on pe +,·,- π* 0 ? p E H 2C π H C CH2 Location Location of +,·,iisat s te ini rm te Reactivity of Allylic Position Reactivity A. Radical Haloge nation C CH H HC Me chanism : I nitiation: 1. Br2 hυ or Δ + Br2 Low conc. C C C Br HHH Faste than addition! r + HBr . 2 Br . + Br . CCC HHH CCC HHH + HBr . Propagation: 2. C C H H HC CCC HHH . Br2 . C C C Br + HHH CCC HHH . Br Te ination: rm Te . + . CH CH Br 3. C H Br2 BrC C C HH H . + Br . Br . CH CH 2 C H C CH H HC CC C HH H Anything that traps radicals, including the“dirt” on thewalls of Anything theflask, contribute to te ination. s rm t he A convenient solid brominating agent: convenient N-Bromosuccinimide, NBS Trace s, Trace always pre nt in NBS se Low Low...
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This note was uploaded on 09/04/2010 for the course CHEM 10966 taught by Professor Vollhardt during the Spring '10 term at Berkeley.

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