What aldehyde is needed to synthesize each amino acid by the Strecker synthesis?

(a) Valine;

(b) Leucine;

(c) Phenylalanine.

In this method, aldehyde is taken with a mixture of ammonium chloride and KCN to form cyanohydrene which then react with excess NH₃ and gives $\mathbf{\alpha }$-aminonitridewhich further undergoes hydrolysis to form amino acid.

In these reactions, cyanohydrene is used as a chemical weapon agent in the reaction and excess of ammonia is used for the removal of hydrogen ion.

(a) 2-methypropanaldehyde reacts with cyanohydrene and forms a compound which on reaction with excess NH_3,a water molecule is removed and $\mathrm{\alpha }-$aminonitride is formed which on further hydrolysis gives valine.

Formation of valine

(b) 3-methylbutanaldehyde reacts with cyanohydrene and forms a compound, which on reaction with excess of NH₃, a water molecule is removed and $\mathrm{\alpha }$-aminonitride is formed which on further hydrolysis gives leucine.

Formation of leucine

(c) Phenyl acetaldehyde reacts with cyanohydrene and forms a compound which on reaction with excess of NH_3, a water molecule is removed and $\mathrm{\alpha }$-aminonitride is formed, which on further hydrolysis gives phenylalanine.

Formation of phenylalanine