Question

11.a) Draw the open chain (Fischer) structure of D-altrose. (1pt)

(b) How many chiral centers are in D-altrose? ______ (1pt)

(c) What is the maximum number of possible stereoisomers whch can exist for D-altrose? _____ (1pt)

(d) Draw L-altrose in open chain form (use Fischer projection) – you may use the space above. (1pt)

(e) Use the information above to draw a Haworth projection for alpha-D-altropyranose. (2pt)

Ruff degradation on a monosaccharide causes C1 to be lost as carbon dioxide, and the Kiliani-Fischer synthesis adds a carbon to the chain by nucleophilic attack, hydrolysis, and reduction of C1. See examples below.

Example of Ruff Degradation:

Example of Kiliani-Fischer Synthesis:

(d) When D-altrose undergoes Ruff degradation to lose a carbon and is lengthened again by one carbon, it is found to be a different monosaccharide. When this monosaccharide is oxidized to form an aldaric acid (oxidized on both ends) it has no optical activity. What is the structure of this monosaccharide?   (2pt)

Ca2+ СНО СОО СНО Н. Н -ОН Fe(OAc)3 FeCl3 Но- 1. Br2/H20 НО -Н Но- НО -Н -Н or СО2 + ОН ОН Н. Н- -ОН Н- 2. Ca(ОН)2 H2О2 30% -ОН ОН Н Н- -ОН Н- сH-он CH2OH CH2OH CH-ОН CN CN СНО Сно о он Он CНО но -Н н -ОН —Н Но н- Он но —Н но -н Но H Нeat но -Н NaCN но- н он Na Н- Он Н -ОН — Он н -Он Н. H НО он CH-ОН Н-0 (Hg) Н- -ОН с Н —он -ОН Н— -он он Н. CH-Он о Оон ОН CH,он CH-он CH,он CH-он он

Answer 1

1. Fischer projection is used to depict 3D molecule in two dimensions. In this atoms or groups are placed in horizontal and vertical directions only.

Fischer projection of D-ALTROSE is

Сно -н но— н- -ОН -он н- н- -он CH-ОН D-Altrose

b. D-altrose has four chiral centers. A chiral center is the atom to which four different groups are attached.

он но но но ОН (2S,3R,4R,5R)-2,3,4,5,6-pentahydroxyhexanal or D-altrose

c. The maximum number of stereoisomers is 2ⁿ, where n is the number of chiral centers. A chiral center is an atom that has four different groups bonded to it

n=4 for given molecule, so

Maximum number of stereoisomers is 2ⁿ =2⁴= 16

d. L-altrose in open chain form (use Fischer projection). D and L are the relative arrangement of atoms with respect to glyceraldehyde. D-glyceraldehyde has OH group on right side the compounds in which Oh is on right side are D isomers. Similarly compounds having OH on left side are called L-isomers

Н н Но- Н- -ОН Н- -ОН Но- —н Но -н Н- -ОН Н- -ОН но- -н CH-он CH20H L-Altrose D-Altrose I