1) Rank the following molecules in order of increasing acidity and briefly explain why they show that order
2) Similar looking sugars can have different relative reactivities. Explain the following observations.
a) Glycosidation of sugar A happens 100,000 times faster than sugar B.
b) Glycosidation of sugar C happens 1000 times faster than sugar D.
3) Acetone can be used to protect adjacent OH groups in a sugar. The protection for ribose is shown below.
a) Draw a curved arrow mechanism for this reaction
b) Why is the primary alcohol not involved in acetal formation?
c) If arabinose is used, the reaction fails. Why?
4) Propose a curved-arrow mechanism for the following reaction (hint – the carbon skeleton of the molecule is unchanged)
5) How might the alkyne in question 5 be synthesized from a smaller alkyne?
6) A reaction of carbohydrates we haven’t seen before is the Wohl degradation, but we can understand it in terms of the functional groups we’ve seen so far. Part of the Wohl degradation is shown below.
a) Draw a curved arrow mechanism for the above portion of the Wohl degradation
b) The following compound could be synthesized from D-mannose. Name AND
draw the aldopentose that would be formed if it is treated as above.
c) An alternate reaction could be for the nitrile to react with NaOH to form an amide (and further react to form a carboxylic acid). Why (1-2 sentences) does this not occur?
7) Give the major product(s) of the following reactions: (you should look up the structures of glucose and other biomolecules in the textbook, on the exam they’d be given to you)
l) Glucose + HNO3
m) Glucose + Br2
n) Glucose + NaBH4
o) Glucose + acetyl chloride (Excess)
p) Glucose + NaOH + CH3CH2Br
q) Glucose + ethanol + acid
8) Draw curved-arrow mechanisms for question 7, parts A, B, D, G, K (step 2 only), and S
9) In this question, if you are given a sugar in cyclic form, draw the Fischer projection. If you are given a Fischer projection, draw the furanose or pyranose as requested.
10) Use the table of aldoses in the textbook for this question.
a) Look up structure of ribose. If ribose is treated with NaCN, what cyanohydrin would be formed? If multiple stereoisomers would be formed, draw both.
b) If the cyanohydrin from part A is then hydrolyzed, what carboxylic carboxylic acid stereoisomers would be formed?
c) In multiple steps, the carboxylic acid can be converted into an aldehyde. Using the table, what aldoses are formed from this chain extension process to ribose? This is 1 way that the structures of the aldohexoses was determined.
d) If you start with D-altrose, what aldoses and ketoses could form from racemization or enolization reactions?
11) Draw disaccharides that contain the following glycoside linkages
a) Glucose-glucose, 1→4
b) Glucose-fructose 1 → 1
c) Galactose-mannose 1 →6
12) Draw curved arrow mechanisms for the following reactions of Acetyl CoA (hint – compare them to similar reactions from chapters 21-22 and abbreviate the CoA side chain).
13) Propose multistep syntheses of the following 2 molecules using any inorganic reagents, and any organic reagents that contain 6 or fewer carbon atoms.
14) Here are the electrostatic potential maps for imidazole and tryptamine. Which of the 2 nitrogen atoms in each compound are more basic? Briefly explain why.
15) Give 1 example of a molecule where the enol form is more stable than the keto form and briefly explain why the enol is more stable.
16) How does the stability of thioesters, phosphate esters, and phosphoric anhydrides compare to the stability of carboxylic esters and anhydrides? Why might nature have chosen to use P and S based compounds?
17) Each of the following reactions will be unsuccessful. For each, explain why the reaction will not work well as written.
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