More examples of addition of hydrogen halides to alkenes: all symmetric.
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Transcript of More examples of addition of hydrogen halides to alkenes: all symmetric.
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more examples of addition of hydrogen halides to alkenes: all symmetric
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What if alkene is asymmetric? Which product forms?
only tert-butyl chloride forms
regiochemistry explained by mechanism
constitutional isomers
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more stable carbocation
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what does the TS look like?
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Hammond postulate: TS most resembles species which is closest in energy
TS III resembles productTS I resembles reactant
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tert-butyl cation forms faster – carbocation formation is rds
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electrophilic addition reactions are regioselective
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Markovnikov rule: electrophile adds to sp2 carbon that is bonded to greater # of carbons
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not regioselective:(draw carbocation intermediates)
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CF3
HBr
F3C H
Br
anti-Markovnikov addition of HBr
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or
will give mix of 2 and 3-bromo product
2-bromo only
synthesis problem:
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acid-catalyzed addition of water to alkenes
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catalyst regenerated
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acid-catalyzed addition of alcohol
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What’s happening here?
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carbocation rearrangementhydride shift
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alkyl (methyl) shift
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ring expansion
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addition of bromine to alkenes
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more stable than carbocation
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haohydrin formation
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explaining regioselectivitythis carbon has more + character
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more variations:
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oxymercuration-reduction: adding water without rearrangements
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source of :H-
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converting alkenes to epoxides
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concerted reaction:
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hydroboration-oxidation: anti-Markovnikov addition of water
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(don’t worry about mechanism of oxidation step, Bruice p. 187)
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catalytic hydrogenation of alkenes
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heats of hydrogenation can be used to compare stability of alkenes
notice: more substituted – more stable
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also: trans more stable than cis
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should be able to show how to do all of these transformations: