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SCAN0024 - " Summam for HX additions HX fl adds first...

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Unformatted text preview: ."\ Summam for HX additions HX: fl adds first to give more substituted R+ (Markovnikov) HBr, ROOR: _B_[ adds first to give more substituted R- (non-Markovnikov) 4. Hydration (Addition of H20) yields alcohols a) Acid-Catalyzed Hydration (Markovnikov) reaction is acid catalyzed; typical hydration medium is 50% HZSO4-50% H20 \/ ll /C—C\ + H-OH —-> H—CIS—T—OH Regioselective: Follows Markovnikov's Rule T6.2 3°,benzylic > 3°,allylic» 2°,benzylic»2°,allylic > 3" > 2°» 1°,allylic >> 1° >> Methyl Know to write the Mechanism: AE involves a carbocation intermediate; it is the reverse of acid-catalyzed dehydration of alcohols to alkenes The more stable the carbocation, the faster it is formed. and the faster the reaction rate. b) Hydroboration-Oxidation (anti-Markov nikov) This method is useful when you want to convert an alkene to an alcohol with a regioselectivity opposite to Markovnikov's rule. Example: M ————> MOH Conditions: 1) BH3'THF complex 2) H202, KOH, H20 Reagents used for hydro boration: 1. Diborane (Bsz) normally used in an ether-like solvent called "diglyme" 2. Borane-tetrahydrof uran complex (HaB-THF) Features onydmbaratz‘an-Oxidation Outcome: hydration of alkenes Regioselectivity opposite to Markovnikov's rule, OH group will end up on the least substituted carbon of the double bond ; no rearrangement Stereochemistry : stereospecific syn addition; H and OH become attached to face of double bond 5} Halogenation {Addition of Cl; or Bra) same ...
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