An unknown acetylenic amino acid obtained from the seed of a tropical fruit has the

Chapter 9, Problem 9.21

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An unknown acetylenic amino acid obtained from the seed of a tropical fruit has the molecular formula C7H11NO2. On catalytic hydrogenation over platinum, this amino acid TABLE 9.4 Electrophilic Addition to Alkynes Reaction (section) and comments General equation and specific example Addition of hydrogen halides (Section 9.11) Hydrogen halides add to alkynes in accordance with Markovnikovs rule to give alkenyl halides. In the presence of 2 mol of hydrogen halide, a second addition occurs to give a geminal dihalide. RC CR' Alkyne HX RCH X R' R R' X X Alkenyl halide Geminal dihalide HX + 2HBr 2,2-Dibromopropane (100%) Hydrogen bromide Propyne BrBr Acid-catalyzed hydration (Section 9.12) Water adds to the triple bond of alkynes to yield ketones by way of an unstable enol intermediate. The enol arises by Markovnikov hydration of the alkyne. Enol formation is followed by rapid isomerization of the enol to a ketone. RC CR' + H2O Alkyne Water R R' O Ketone H2SO4 Hg2+ + H2O H2SO4 HgSO4 O 1-Hexyne Water 2-Hexanone (80%) Halogenation (Section 9.13) Addition of 1 mol of chlorine or bromine to an alkyne yields a trans dihaloalkene. A tetrahalide is formed on addition of a second equivalent of the halogen. RC CR' Alkyne X2 R R' X X Dihaloalkene Tetrahaloalkene X2 R R' X X X X + 2Cl2 Cl ClCl Cl Propyne Chlorine 1,1,2,2-Tetrachloropropane (63%) 364 Chapter 9 Alkynes car02745_ch09_342-369.indd 364 10/3/12 3:20 PM yielded homoleucine (an amino acid of known structure shown here) as the only product. What is the structure of the unknown amino acid? O O NH3 Homoleucine