Chemistry 342 M. Walker
Practice Final Exam
YOUR NAME______________________________
360 points total. You may use molecular models
for this exam.
2. (20 points) Explain (using resonance forms) why 2,4-pentanedione is more acidic than 2‑pentanone.
3. (12 points) Draw structures for any two of the following compounds.
(a) 3-amino-4-methylbenzaldehyde
(b) 3-bromo-2-cyclohexenone
(c) 2-(4-nitrophenyl)butanoic acid
4. (100 points total) The following questions all refer to the reaction schemes shown below. These are taken from a paper in a 1998 issue of the "Journal of Organic Chemistry". Note that NaH, sodium hydride, serves the same purpose as LDA.
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(a) (20 points) Give a full mechanism for the first reaction, the preparation of 7 using diethylamine.
4.(contd.) (b) (15 points) The preparation of 4g involves the enolate of an amide. Draw all three resonance forms of this enolate.
(c) (10 points) The preparation of 8a involves the anion of a nitrile (2-methylpropanenitrile). Draw both resonance forms for this anion.
(d) (20 points) For the preparation of a dicarbonyl system such as in 4h, 4i, the Claisen condensation is usually used (see, for example, the preparation of 4e, 4f), because of the thermodynamic driving force which assists most Claisen condensations. However these authors instead chose to perform an aldol condensation followed by an oxidation (actually using K2Cr2O7/H+). Why is the Claisen less favored than usual in this specific case? [Hint: the nitrile anion is not connected with the reason- a simple enolate anion would react similarly.]
4.(contd.)(e)(10 points) Give a full mechanism for the alkylation of the enolate shown, and show the alkylation product:
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5. (45 points) How might you effect the following transformations in a practicable manner? Some conversions may require more than one step.
6. (50 points) Synthesize any two of the following using the starting materials shown, and any legitimate reagent of two carbons or less. You may also use formate or acetate esters, dithiane and phthalimide.
7. (16 points) For each set of three compounds, circle the most acidic.
8. (20 points) Dithiane is a useful reagent for the synthesis of ketones and aldehydes.
(a) Give a mechanism for the formation of dithiane from 1,3-propanedithiol and formaldehyde.
9. (25 points) Fill in the boxes in the following synthesis with structures or reagents as necessary. Include stereochemistry where appropriate, and indicate if racemic or not.
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