=========================preview======================
(chem313)[2008](s)mid~PPSpider^sol_10048.pdf
Back to CHEM313 Login to download
======================================================
CHEMISTRY 313 INTERMEDIATE ORGANIC CHEMISTRY

Mid-Semester Examination Answer Key

Friday April 11 2008 Room 2406 Time Allowed: 120 minutes
--------------------------------------------------------------------------------------------------------------------------------------------
Enter your name, and student ID number, on the beige answer booklet. Answer all questions. Read the questions carefully before answering. There is a total of 120 points for this examination paper.
--------------------------------------------------------------------------------------------------------------------------------------------


1a. Consider the compounds 1a-1f




i.
Draw the Fischer projections for compounds 1a, 1b and 1c. (9 pts)







ii.
What is the stereochemical relationship between 1a and 1b? (1 pt): diastereomers


iii.
Assign configuration at the chiral (chirogenic) centres as 'R' or 'S' in those compounds which contain such centres. (8 pts)







iv. Select one compound which contains a pseudoasymmetric centre and label the centre as 'r' or 's' (2 pts). Two compounds C 1a and 1f - see above

v. Select one compound which contains homomorphic groups, and identify the groups. (2 pts). compound 1b only; contains two sets of such groups as indicated below.


vi. Select one compound which contains enantiomorphic groups, and identify the groups. (2 pts) compound 1a contains two sets of such groups as indicated below; compound 1f.

RRRRRRRRSSSRRSrrsRRRRRRSSRSSRSRSRSRRRRRRRRRRRRRRRRRRRSSRRRRSRRRSRRRRRRR:SRRR0SRRSRSSRSSRRS BrBrCCNNCCNNNNNNCNNHNHNN2-RRRSRRRRRRRRSHHUnstable


vii. Select one compound which contains a prochiral centre, and assign the attached ligands as 'pro-R' and 'pro-S' respectively. (4 pts). Easiest are compounds 1d and 1e. Ha is pro-R, and Hb is pro-S in compounda 1a and 1b:




viii. Select one compound which contains diastereotopic ligands, and identify them. (2 pts). Question is difficult; need to think carefully, best to use Fischer projections which show H atoms.




ix. Select one compound which contains hetereotopic faces. Identify these either as enantiotopic or diastereotopic, and label as 'Si ' or 'Re' as appropriate. (3 pts) Compound 1f; simplest to consider nucleophilic addition to just one carbonyl group.



x. Compound 1c is in equilibrium with two cyclic six-membered chair forms. Give the stereostructures of these cyclic forms, and label as '' and '' respectively. (5 pts) Compound 1c is glucose C see Stereochemistry Part II, Slides 3, 33:




1b. Consider compounds 1g and 1h.




i. Given that the A values for the p-toluenesulfonate group (-OTs or -OSO2C6H4CH3-p) is 0.50 kcal mol-1 and the N,N-diethylamino group [CN(CH2CH3)2] is ~2.8 kcal mol-1, draw out the more stable chair conformer for each of the compounds 1g a