An important reaction used by Emil Fischer in his research on carbohydrate chemistry was the reaction of aldoses and ketoses with phenylhydrazine to give osazones, shown in Fig. P24.44. Osazones, unlike many carbohydrates, form crystalline solids that are useful in characterizing carbohydrates.

(a) Glucose and mannose give the same osazone. Given that these two compounds are aldohexoses, what could a scientist who knows nothing about the stereochemistry of these carbohydrates deduce about their stereochemical relationship from this fact?

(b) What aldopentose gives the same osazone as D-arabinose?

Transcribed Image Text:

CH O CH-OH 1 CH-OH CH-OH CH-OH T CH₂OH + 3 PhNHNH, phenylhydrazine an aldose Figure P24.44 CH=NNHPh C=NNHPh CH-OH CH-OH CH-OH T CH₂OH an osazone + NH3 + PhNH, + 2 H,O