lecture 5

• Hydration of alkenes

  Alkenes can be hydrated by H2O in the presence of strong acids
• Markovnikov's rule


  Reaction via the most stable cation

  (OH at most substituted carbon)
• Hydration of alkenes with Hg2+


  -alkenes can be hydrated using soft lewis acids such as Hg2+

  -1) Hg(OAc)2 and H2O

  2) NaBH4
• Hydroboration/Oxidation of alkenes

  -Alkenes react with BH3 to form Alkyl Boranes

  -Then oxidised with H2O2 and NaOH to give alcohols
• Hydroboration of alkenes mechanism of reaction

  -2,2 addition of B-H bond and C=C bond

  -steric hinderance decided where BH3 substitutes

  -Addition of BH3 on least hindered face of an alkane

  -oxidation of C-B bond by NaOH/H2O2

  -hydrolysis of B-O bonds in basic conditions
• RBH2 addition

  -Highly hindered alkenes -BH3 will on add to one alkene only

  -RBH2 add to two alkenes

  -allows highly regioselective hydroborations
• Highly selective hydroboration

  9-BBN

  -allows conversion of terminal alkynes to aldehydes