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What is hemolytic bond dissociation?
When one electron in a bond goes to one atom, and the other electron goes to another atom. This is done with the one sided arrow
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Radicals are not very common because they require such a large _____
Bond dissociation energy
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_____ have the lowest bond dissociation energy
Halogens
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What is used to create free radicals? (Found on the lower arrow)
Light energy or heat
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What are radical initiators, and what are some examples of them?
Molecules with weak bonds that can easily be broken
The halogens- Br2, Cl2, I2
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From most to least stable, what is the ranking of alkyl radicals?
Benzene > allylic > 3 >2 > 1 > methyl
Treat them like carbocations --> the more substituted the carbon is, the more EDG's around it and the better it is able to handle the radical
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Radicals do or do not undergo rearrangements like carbocations?
Do not
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_____ are used to depict the delocalization of radicals, where the blue represents ____ and the red represents _____
Electron spin density
Radicals
Paired electrons
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What is homolytic cleavage (initiation)
When the initial radical is formed, where one electron goes to one molecule and another electron goes to the other molecule
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What is propagation (addition to a pi bond)?
When a radical is added to a pi bond, linking that atom with a new bond and creating a new radical
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What is SH2/hydrogen abstraction (propagation)?
When the radical bonds to a hydrogen
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What is SH2/halogen abstraction (propagation)?
When the radical bonds to a new halogen
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What is elimination (propagation)?
When the radical pushes back into the molecule to force another group to leave
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What is radical coupling (termination)?
When two radicals combine to form a normal bond
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What are the common steps in a radical mechanism?
Initiation- where the radical is formed
Propagation 1
Propagation 2- usually a new radical is formed here, so it also includes an initiation step
Termination- where the two radicals come together to bond normally
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What are the more feasible halogens to use in radical halogenation and why?
Br2 and Cl2 because their bond dissociation energies are right in the middle, so they react fast enough to not take forever, but slow enough that they don't cause explosions
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____ is more selective than ____ because
Bromine
Chlorine
Bromine has a late transition step, which means the process in choosing which product to make is slower and more selective
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What are the two things needed to predict the regiochemistry/ percentage of products formed?
The number of hydrogens who's substitution produces the same product
The relative rates of each type of hydrogen (3,2,1)
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What is the reagent used in radical bromination?
Br2
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What is the problem when bromination is carried out with Br2 and light, and what is the reagent that's used to solve the problem?
Adding Br2 will result in an EAS reaction where Bromine is added across the double bond.
To get one Bromine added to the ring, use NBS
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What is the reagent used in free radical bromination?
NBS
It keeps the concentration of the molecular bromine and the bromine radical low
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The radical addition of HBr is anti markovniv or markovnikov?
Anti-markovnikov
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What is the reagent needed to keep the addition of HBr antimarkovnikov?
Peroxides
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In radical addition of HBr, the radical will be placed on the _____ substituted carbon
Most
Makes the most stable radical product, just like we would with the creation of the carbocation
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The free radical reaction is a ______ reaction and produces a _____ mixture
Stereoselective
Racemic
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What is a dissolving metal reaction?
When a metal (usually Na or Li) is dissolved in the solution along with the reactants
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What are the reaction conditions for dissolving metal reactions?
- A metal solid (usually Na or Li)
- Liquid ammonia (NH3)
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What is the result of a dissolving metal reaction?
A solvated electron
Just a single electron in the solution
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What is anti-hydrogenation? What is the isomer that forms?
When two hydrogens are added to a triple bond in an anti (trans) fashion. It is the result of a dissolving metal reaction
Creates the trans alkene because it is more stable
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A dissolving metal reaction will selectively reduce an _____ over an _____
Alkyne
Alkene
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During anti-hydrogenation, one carbon will have a ____ charge, while the carbon next to it will be a ____
Negative charge
Radical
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What happens in a Birch reduction? What reagents are needed?
Reduces benzene to cyclohexa-1,4-diene. The reaction stops after a single hydrogenation.
- A metal (Na or Li)
- Tert-buytl alcohol, NH3, THF, at room temperature
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The Birch reduction yields only the _____ product
1,4
These are the positions to which the hydrogens are added
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What are the three ways in which radical inhibitors prevent radicals from reacting with anything?
- Resonance
- Induction
- Sterics
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What is autooxidation?
The process by which compounds will react with molecular oxygen
Can cause explosions
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What is the name of one radical inhibitor?
BHT
Alcohol with two test-butyl groups to the side and a methyl on the bottom of the ring
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