Question

A) Starting with the linear form shown in Figure 7-3a, show the cyclization reaction(s) of D-xylose to create all possible cyclized forms. Name the cyclized forms. Note: you can ignore the less stable four and seven membered rings. (4 marks) B) Draw and name two cyclic epimers of the D-xylose, highlighting the chiral center involved. (2 marks) C) How many asymmetric carbons (chiral centers) are there for each of the cyclised D-xylose structures in part A compared to the linear form? Explain. (3 marks) D) How many stereoisomers of linear D-xylose are theoretically possible? (1 mark) E) How many stereoisomers of cyclised D-xylose are theoretically possible and what is a general formula for cyclized aldopentose stereoisomers? (2 marks) F) Draw L-xylose. (1 mark)

Answer 1

HOCH₂ anomeric Couson HOCH, H OH DH HM Hot 애 내 O // HoHoH И но и HV V on h H -OH L-D Xylose, SCHLOH. D- Xylose, NOTES • Groups on the right in a cyclic linear projection are down in a cyclic projection. • Groups on the left, in a linear projection are ß-D xylose up in cyclic projection. # Exclic projections are called Howarth brojections a we are two sugars that differ in configration only at hon that was the carbonyl carbon in the This Topen- carbon is called the anomeric carbon.. the form. This carbon chain

c) linear form :- cyclic form HOCH OH HOR H0 -*_* H on HO OH WO CH,OH, D- Xylose. |кі анч- chiral centers. L-D Xylose There are 3-chiral centers, group i. c. carbonyl chinal. converts On cyclidation the alcoholic group into 1st carbon and become 4-c=0 F.) L-Xylose, non l - forum D of is D- the mirror foum. image 'no- CH₂OH

Epimere :- Diastereomers that differ in configuration at only asymmetric center are called epimens one HO ta. a epimer tot C2. Hoon HOLH. HOH CHOH. D-Xulose, HOH H OH CHOH. D-lynose, Cyclic form, : - HOCHO -ebimer HO CH₂OH HOHHO/OH, NOH Hol. Kad son. nd