Question

How can you identify a specific unknown aldehyde or ketone?

Answer 1

We can identify an unknown Aldehyde or ketone by combination of modern and classical technique.

1.First we will take the IR spectrum .We will get a strong peak between 1700 to 1730 cm^-1 which corresponds to CO bond of carbonyl.

2.Now we will take ¹H NMR spectrum if we get a peak between 9-10 ppm its usually correspond to aldehyde hydrogen.Ketone will not have a peak in this region..

3.Then make semicarbazone derivative of unknown sample.dry the crystal and measure the melting point

4.Make 2,4-dinitrophenylhydrazone derivative of unknown sample.Collect the precipitate .Recrystallize the precipitate with minimal amount of ethyl alcohol .then filter and dry the crystal and then measure the melting point.

from the melting point value we can identify the ketone or aldehyde.

these 2 derivatization may not work with all the unknown but atleast one will work well.