oat orgo unit 12

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free radical

a molecule or atom with an unpaired electron, formed by homolytic bond cleavage, caused by heat or light (produces two radicals)

carbon radicals

Contain an unpaired electron and are considered electron deficient. They follow the same trends as carbocations, and the unpaired electron goes in the p orbital.

free radical stability

free radical reaction steps

initiation, propagation, and termination.

initiation

Homolytic cleavage of a stable molecule’s weak covalent bond to produce two radicals.

• Endothermic

• Highest activation energy

• Rate determining step

propagation

A radical reacts with a stable molecule, simultaneously producing another radical.

termination

Two radical species react together to produce a stable molecule.

free radical bromination

• The major product is alkyl bromide. Br is attached to the most stable carbon that originally contains a hydrogen due to regioselectivity.

• Reagents: Br₂, heat/light(hv)

• If a chiral center is made, it makes a racemic mixture

free radical chlorination

Same as FR bromination, but the final product is not regioselective, meaning every carbon with a hydrogen on it will form an alkyl chloride.

allylic position

carbon adjacent to the alkene double bond

benzylic position

The carbon adjacent to a benzene ring.

NBS

reagent that is used to brominate allylic and benzylic carbons, accompanied by light or heat. It ensures that bromine will be added somewhere other than the pi bond.

Allylic bromination

benzylic bromination

diene

conjugated molecule with alternating single and double bonds.

• Must be in s-cis conformation for a Diels alder cycloaddition (image)

• Something locked in the s-cis position is a very good reactant, and something locked in the s-trans position can’t react.

dienophile

alkene or alkyne that reacts with a diene in Diels Alder cycloaddition.

diels alder cycloaddition

• Produces a six membered ring.

• Concerted mechanism where 3 pi bonds produce 2 sigma bonds and 1 pi bond.

• Stereochemistry is maintained.

• Endo product is formed

endo and exo diels alder products

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