22_all_ - 22.1 How many stereocenters are contained in the...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
22.1 How many stereocenters are contained in the (a) aldotetrose and (b) ketopentose just given? (c) How many stereoisomers would you expect from each general structure? CH CHOH CHOH CH 2 OH C CHOH CHOH CH 2 OH O CH 2 OH O An aldotetrose A ketopentose The answer: Each of them has two stereocenters. Both of them have four stereoisomers 22.2. Write three-dimensional formulas for each aldotetrose and ketopentose isomer in Problem 22.1 and designate each as a D or L sugar. CH O C OH H HO H CH 2 OH CH O C OH H HO H CH 2 OH CH O C H HO H CH 2 OH CH O C H HO HO H CH 2 OH D sugar L sugar D sugar L sugar C H O CH 2 OH OH H CH 2 OH C H O CH 2 OH H HO CH 2 OH C HO H O CH 2 OH OH H CH 2 OH C HO H O CH 2 O H H HO CH 2 OH D sugar L sugar D sugar L sugar
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
22.3 (a) What products would be formed if salicin were treated with dilute aqueous HCl? (b) Outline a mechanism for the reactions involved in their formation. Answer: (a) O HOH 2 C HO HO OH OH O HOH 2 C HO HO OH + (b) O HOH 2 C HO HO OH O CH 2 OH O HOH 2 C HO HO OH OH 2 O HOH 2 C HO HO OH OH 2 O H H H O HOH 2 C HO HO OH H O CH 2 OH O HOH 2 C HO HO OH H 2 O O HOH 2 C HO HO OH OH O HOH 2 C HO HO OH OH 22.4 How would you convert D-glucose to mixture of ethyl α -D-glucopyranoside and ethyl β -D-glucopyranoside? Show all steps in the mechanism for their formation. Answer:
Background image of page 2
CHO H OH HO H H OH H OH CH 2 OH O HOH 2 C HO HO OH OH H 3 O + O HOH 2 C HO HO OH OH 2 O HOH 2 C HO HO OH EtOH O HOH 2 C HO HO OH OEt O HOH 2 C HO HO OH OEt O HOH 2 C HO HO OH OEt O HOH 2 C HO HO OH OEt H H 22.5 In neutral or basic aqueous solutuions, glycosides do not show mutarotation. However, if the solutions are made acidic, glycosides do show mutarotation. Explain why this occurs. Solution: Glycosides are acetals, and they do not exist in equilibrium with aldose or ketose in neutral or basic aqueous solutions. So glycosides do not show mutarotation. But they will be converted to sugar and alcohol in acidic solutions, then sugar will show mutarotation. 22.6 How might you distinguish between α -D-glucopyrannose (i.e., D-glucose) and methyl α -D-glucopyrannoside? Solution: We can test them with Tollen’s Reagent. If it gives positive test, it is α -D-glucopyrannose. Otherwise it is methyl α -D-glucopyrannoside. 22.7 (a) Would you expect D-glucaric acid to be optically active? (b) Write the open-chain structure for the aldaric acid (mannaric acid) that would be obtained by nitric acid oxidation of D-mannose. (c) Would you expect mannaric acid to be optically active? (d) What aldaric acid would you expect to obtain from D-erythrose? (e) Would the aldaric acid in (d) show optical activity? (f) D-Threose, a diasterreomer of D-erythrose, yields an optically active aldaric acid when it is subjected to nitric acid oxidation. White Fischer projection formulas for D-threose and its
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
nitric acid oxidation product.
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/23/2010 for the course CHEM 101 taught by Professor Smith during the Spring '10 term at Duke.

Page1 / 27

22_all_ - 22.1 How many stereocenters are contained in the...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online