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School of Chemistry
Semester 1
CHEM20018
Reactions and Synthesis
Section A — Synthesis: Organic Compounds
Total = 60 marks
Answer ALL questions (1 - 7) in this section.
Question 1 (5 + 5 + 5 = 15 marks)
(a) Draw all possible enol or equivalent tautomeric forms for each of the two structures shown below:
(b) Outline a one-step synthesis for each of the following compounds, starting from simpler carbonyl precursors and any other necessary reagents. Mechanistic detail is not required.
(c) Using common reagents as needed, show how the following chemical conversion can be carried out. This will require more than one step and will need to employ other carbonyl-containing precursors, besides the one shown. Mechanistic detail is not required.
Question 2 (3 + 3 + 3 + 3 + 3 + 3 = 18 marks)
Write a structure for the major product expected from each reaction in the following parts (a) - (f) below. Stereochemical considerations and mechanistic detail are not required.
Question 3 (5+5+5 = 15 marks)
(a) Write structures for compounds O and P involved in the following chemical sequence. Molecule O has the molecular formula C4H6O2. Mechanistic detail is not required.
(b) Write a structure for compound Q (shown below) involved in the following chemical conversion. Mechanistic detail is not required.
(c) Write structures for compounds R, S and T in the following chemical conversion. Compounds R and S are ß-keto esters.
Question 4 (3+2+2+2+3 = 12 marks)
D-Tagatose is a 2-ketohexose. Treatment of D-tagatose with the mild base sodium acetate (CHsCO2Na) results in keto-enol tautomerism to two aldohexoses, one of which is D-talose. By consulting the D-sugar family tree (see Appendix), answer the following:
(a) Draw a Fischer projection for the structure of the other aldohexose (ie not D-talose) formed upon keto-enol tautomerism of D-tagatose. Provide a name for this compound.
(b) Draw a Fischer projection of D-tagatose.
(c) Draw a Fischer projection of the enol tautomer of D-talose.
(d) Draw the cyclic Haworth structure of D-talopyranose.
(e) Reaction of two molecules of D-talopyranose can generate the β-1,4-linked disaccharide "talobiose". Draw talobiose, being sure to carefully represent the stereochemistry (ie α or β) and regiochemistry (the 1,4-linkage) of the disaccharide.