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(chem313)[2009](s)midterm~PPSpider^_10049.pdf
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CHEMISTRY 313 INTERMEDIATE ORGANIC CHEMISTRY

Mid-Semester Examination

Friday 3 April 2009 Lecture Theatre E 18:00-20:00 Time Allowed: 120 minutes

There is a total of 120 points for this examination paper.

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. Enter your name and student ID number on the beige answer booklet.

. Answer all questions.

. Read the questions carefully before answering. If you have difficulty with a question, leave it and go on to another question

. You may write your answers on all pages of the answer booklet. If you have rough working, please cross it out and mark 'rough work'

. You are reminded of the University guidelines on plagiarism (cheating). If anyone is caught cheating, they will be asked to leave the examination room, and a fail grade will be entered in the first instance


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Draw structures clearly, with stereochemistry unambiguously and clearly indicated. Marks will be deducted for poorly-drawn structures.


Do not open this examination question paper until you are instructed to do so.

1ai. Indicate as precisely as possible the isomeric relationship, if any, including the use of any unique names that may be used to described the nature of the relationship, between each of the following pairs of compounds. Barriers to rotation/inversion at 25 C are given. (6 pts) HHHHCH3HHHCH3HCH3HHHCH3HCH3CH3CH3CH3

i: .G. > 66 kcal mol-1 ii: .G. 0.8 kcal mol-1 iii. .G. 12 kcal mol-1 iv: .G. 23.5 kcal mol-1 v: .G. 8.0 kcal mol-1 vi: .G. 1.0 kcal mol-1 See Slides 27, 28, Stereochemistry, Part I - i: atropisomers - diastereomers (accept configurational diastereomers); ii: conformational enantiomers; iii: conformational enantiomers; iv; atropisomers C enantiomers (accept configurational enantiomers); v: conformational diastereomers; vi: conformational diastereomers. ii. Consider the enantiomerically pure compound 1a. Under aqueous acidic conditions, this is hydrolysed to compound 1b. Comment on the stablity of 1b. Do you think it would be possible to isolate this compound as the pure enantiomer at room temperature? Give a reason. (5 pts) The question focusses on the stability of compound 1b, which is obtained by hydrolysis of 1a. The second part of this question C do you think it is possible to isolate compound 1b - obviously depends upon whether compound 1b is stable. The answer is simple: compound 1b is unstable because of equilibration between tautomers: Compound 1ba is the keto tautomer of compound 1b. It has no chiral (chirogenic) centre, therefore is achiral. Compound 1bb is the