1.  Theoretical definition of reduction

         a)  gain of electrons
         b)   reducing of oxidation number

                 i)   Cr⁺⁶ + 2e^- -> Cr⁺⁴


2.   Opposite of oxidation


3.  Typical reducing reagents

         a)  catalytic hydrogenation

                 i)  H₂/Pt

                         a)   high temperature
                         b)   high pressure
                         c)   not selective (C=0 and C=C)

         b)   Hydride (H^-) Transfer Reageants

                 i)   NaBH₄



                         a)   selective - only



                         b)   mild
                         c)   reduces aldehydes to 1° alcohols and ketones to 2° alcohols
                         d)   four moles of H^- per mole of BH₄^-


2)   LiAlH₄



         a)   stronger
         b)   reduces acids, esters and aldehydes to 1° alcohols, ketones to 2° alcohols.
         c)   explosive with H₂O
         d)   4 moles of H^-/mol AlH₄^-


3)   LiAl(tBuO)₃H



         a)   selective for acid chlorides to aldehydes

                 i)   single H^-
                 ii)   low temperature
                 iii)   steric hinderance


4)   All are selective for the C=O group and will not reduce to C=C

5)   The hydride transfer mechanism



Note:   The H₂ produced from the above reaction is not the H₂ the students observe upon addition of NaBH₄