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Org 1 Review - Free Radicals

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winterflower's version from 2016-09-11 03:36

Section

Question Answer
When the net number of radical species during a reaction is increased, this is ____ Increase ---> this is initiation
when the net number of radical species during a reaction remains the same, this is _____Stay the same --> this is propagation
When the net number of radical species in a reaction decreases, this is _____ Decrease --> this is termination
During the course of the free-radical chlorination of methane, a small amount of hexachloroethane (C2Cl6) is produced in addition to carbon tetrachloride (CCl4). How do you explain this?This is explained through a small amount of termination through joining together of CH3 radicals followed by subsequent chlorination. (Actually it doesn't have to be CH3 - the chlorinated derivatives can do this too).
What's the easiest C-H bond to break through homolytic cleavage - H-CH3, H-CH2CH3, H–C(CH3)2, H–C(CH3)3 . Easiest bond to break through homolytic cleavage is H–C(CH3)3 and the hardest is H–CH3. This is because the tert-butyl radical is much more stable than the methyl radical.
In the free radical halogenation of propane, which would you expect to form a greater amount of 2-halopropane relative to 1-halopropane - Cl2 or Br2? Br2 forms greater relative amount of 2-bromopropane. The HBr bond is weaker. (Compare chlorine and bromine to two people walking into a store to buy an item. Bromine, having less "money" to spend, will be more sensitive to "price" (stability of the radical formed) than chlorine will. Chlorine will "buy" more indiscriminately).
Why is NBS preferred over Br2 for allylic bromination?NBS will not lead to dibrominated products whereas Br2 will.
Which forms stronger bonds to hydrogen, bromine or chlorine? chlorine
which reactions should be more energetically favorable, chlorination of alkanes or bromination of alkanes?chlorination
which should have a higher activation energy, chlorination of alkanes or bromination of alkanes?bromination will have higher activation energy
which should be more "selective" for discriminating between tertiary C-H, secondary C-H, or primary C-H bonds, chlorination of alkanes or bromination of alkanes ?bromination will be more selective
True or false: free radicals are electron-deficient species. True - they don't have a full octet and are thus electron deficient.
When a free radical such as Br• adds to an alkene, the result is the "anti-Markovnikoff" product. Why?Driving force is formation of more substituted radical. When Br• adds to the alkene it will preferentially add to the less substituted end because this will put the radical on the more substituted position (where it is more stable)
What two factors stabilize free radicals? Substitution (tertiary is more stable than secondary which is more stable than primary) and also resonance.
True or false: in the initiation step, all Br2 is converted into Br radicals False - at any given time you only have a small amount of Br radicals, but they are sufficient to carry out the chain reaction.
What's allylic bromination? Allylic bromination - remove an allylic H through abstraction by Br radical, then the allylic radical reacts with Br2 to give allyl bromide and regenerate the Br radical.
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