Write the reaction of ethanal which …

A typing error !  Pl. read   as , 

.......................................CH₃ ** C* H  O   , instead  of  H₃ ** C* HO

  Thanks,

Aldehydes and ketones exhibit the  unusual acidity of hydrogen atoms attached to Carbons - alpha  (   {tex}\alpha{/tex}  )  which is  adjacent  to that of  the carbonyl group. These hydrogens are referred as  {tex}\alpha{/tex} - hydrogens , and the carbon atom to which they  are bonded is {tex}\alpha{/tex}- carbon. In ethanal there is one {tex}\alpha{/tex}  C* & three {tex}\alpha{/tex}. - H  atoms ( marked as H** ).

................................H₃ **  .C*  H O

although weakly acidic ,  ( K_a  =  10^-19  to 10^-20 )  {tex}\alpha{/tex} - H can react  with strong bases to form anion . The unnusual acidity of {tex}\alpha{/tex} - H can be explained by both electron withdrawing ability of the carbonyl ( =CO ) group ,and resonance in anion that is formed . The electron withdrawing ability  of   =CO group is  caused by the groups di[pole nature which results by difference in electronegativities  of   C  and  O atoms.

The anion formed by loss of {tex}\alpha{/tex} - hydrogen can be resonance stabilised because of mobility of {tex}\pi{/tex} - electrons that are adjacent to carbonyl group ( =CO ) . This resonance which stabilises the anion ( commonly termed as  enolate ion ) creates two resonance structures  , an enol & a keto-form . In most cases the keto form is more stable. 

The reaction is very well termed as Aldol condensation . In case of ethanal this reaction , in the simplest form , can be represented as -

2CH₃ CHO  <------dil .NaOH ----------->   CH₃ - CH (OH) -CH₂ -  CHO------------- {tex}\Delta{/tex} /  ( - H₂ O ) ------------->   CH₂ - CH=CH - CHO. -

Ethanal...................................................3- Hydroxybutanal.....................................................................But -2 - enal(

....................................................................( Aldol ).....................................................................( Aldol condensation product )