Concept Summary

General Principles

Enolate Chemistry

The carbon  adjacent    to  the carbonyl    carbon  is  termed  an  α-carbon;   the hydrogens   attached    to

the α-carbon    are called  α-hydrogens.

α-Hydrogens are relatively  acidic  and can be  removed by  a   strong  base.

The electron-withdrawing    oxygen  of  the carbonyl    weakens the C–H bonds   on  α-carbons.

The enolate resulting   from    deprotonation   can be  stabilized  by  resonance   with    the carbonyl.

Ketones are less    reactive    toward  nucleophiles    because of  steric  hindrance   and α-carbanion

destabilization.

The presence    of  an  additional  alkyl   group   crowds  the transition  step    and increases   its energy.

The alkyl   group   also    donates electron    density to  the carbanion,  making  it  less    stable.

Aldehydes   and ketones exist   in  the traditional keto    form    (C=O)   and in  the less    common  enol

form    (ene    +   ol  =   double  bond    +   hydroxyl    group).

Tautomers   are isomers that    can be  interconverted  by  moving  a   hydrogen    and a   double  bond.

The keto    and enol    forms   are tautomers   of  each    other.

The enol    form    can be  deprotonated    to  form    an  enolate.    Enolates    are good    nucleophiles.

In  the Michael addition,   an  enolate attacks an  α,β-unsaturated carbonyl,   creating    a   bond.

The kinetic enolate is  favored by  fast,   irreversible    reactions   at  lower   temperatures    with    strong,

sterically  hindered    bases.  The thermodynamic   enolate is  favored by  slower, reversible  reactions

at  higher  temperatures    with    weaker, smaller bases.

Enamines    are tautomers   of  imines. Like    enols,  enamines    are the less    common  tautomer.