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Mobile App Chapter 20: Q18P (page 962)
Identify A, B, C, and D in the preceding problem if D is oxidized to an optically inactive aldaric acid; if A,B, and C are oxidized to optically active aldaric acids; and if interchanging the aldehyde and alcohol groups of A leads to a different sugar.
Short Answer
- D-glucose is identified as Compound A.
- D-mannose is identified as Compound B.
- D-arabinose is identified as Compound C.
- D-erythrose is identified as Compound D.
Step by step solution
Identification of compound A
Compound A in the preceding problem was “D-galactose,”which is oxidized to optically active aldalric acid;it must be d-threose having -OH group on the right side inthe asymmetric carbon (2nd carbon from the bottom)in the A compound.
Carbohydrate having 2nd carbon from the bottom with -OH group at the right and rest all the same as in D-galactose is D-glucose.
Therefore,compound A becomes D-glucoseafter oxidizing to active aldalric acid.
The structure of D-glucose is shown as follows:
Structure of D-glucose
Identification of compound B
Compound B in the preceding problem was “D-talose,”which is oxidized to optically active aldalric acid;it must be d-threose having -OH group on the right side inthe asymmetriccarbon (3rd carbon from bottom)in the B compound.
Carbohydrate having 3rd carbon from the bottom with -OH group at the right and rest all the same as in D-talose is D-mannose.
Therefore, compound B becomes D-mannoseafter oxidizing to active aldalric acid.
The structure of D-mannose is shown as follows:
Structure of mannose
Identification of compound C
Compound C in the preceding problem was “D-xylose”oxidized to optically active aldalric acid; it must be d-threose having -OH group on the right side in the asymmetric carbon (3rd carbon from the bottom)in the C compound.
Carbohydrate having 3rd carbon from the bottom with -OH group at the right and rest the same as D-xylose is D-arabinose.
Therefore, compound C becomes D-arabinoseafter oxidizing to active aldalric acid.
The structure of D-mannose is shown as follows:
Structure of D-arabinose
Identification of compound D
Compound D in the preceding problem was “D-threose.”oxidized to inactive aldalric acid;it must be D-erythrose having -OH group on the left in the asymmetric carbon (2nd carbon from the top)in the D compound.
Carbohydrate having 2nd carbon from the top with -OH group at the right and rest the same as D-threose is D-erythrose.
Therefore, compound D becomes D-erythroseafter oxidizing to optically inactive aldalric acid.
The structure of D-erythrose is shown as follows:
Structure of D-erythrose
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