Dolbier HW Solutions 435

Dolbier HW Solutions 435 - 529 CARBOXYLIC ACIDS The...

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The precursor has the same carbon skeleton as the designated starting material. All that is necessary is to hydrogenate the double bond of the alkynoic acid to the cis alkene. This can be done by using the Lindlar catalyst. Cyclization of the hydroxy acid to the lactone is spontaneous. 19.31 Hydration of the double bond can occur in two different directions: ( a ) The achiral isomer is citric acid. ( b ) The other isomer, isocitric acid, has two stereogenic centers (marked with an asterisk*). Iso- citric acid has the constitution With two stereogenic centers, there are 2 2 , or four, stereoisomers represented by this constitu- tion. The one that is actually formed in this enzyme-catalyzed reaction is the 2 R ,3 S isomer. 19.32 Carboxylic acid protons give signals in the range d 10 12 ppm. A signal in this region suggests the presence of a carboxyl group but tells little about its environment. Thus, in assigning structures to
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