(a) Illustrate the Strecker synthesis of phenylalanine. Is the product chiral? Does it exhibit optical activity? 

(b) It has been found that replacement of NH₃ by an optically active amine in the Strecker synthesis of phenylalanine leads to an excess of one enantiomer of the product. Assign the R or S confi guration to each stereocenter in the following structures, and explain why the use of a chiral amine causes preferential formation of one stereoisomer of the final product. 

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NH2 HCN H;C H CH2 H C-N TH H,C 1. H*, H,O 2. Н, Ра- С CH,CH -CH2 Hc-NH3 -H,0 c–NH3 H NC CO0 Mainly Mainly