UCSC, Binder. CHEM 8B Organic Chemistry II FINAL EXAM (300 points)

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1 UCSC, Binder Name CEM 8B rganic Chemistry II FINAL EXAM (300 points) In each of the following problems, use your knowledge of organic chemistry conventions to answer the questions in the proper manner. Be sure to read each question carefully. You have 3 hours to complete the exam, but hopefully you won t need it! You are welcome to use pre-built models. Keep your eyes on your own paper. Electronic devices, study guides, and cheat sheets of any kind are not allowed, including cell phones and calculators. Any student found using any of the above devices or found examining another student s exam will be promptly removed from the room and will receive a zero on this exam. Such an incident may also be reported to the UCSC Judiciary Affairs Committee. 1. Nomenclature & FUNdamentals (45) 2. Amino Acids & Peptides (35) 3. Reactions, MC (20) 4. Reaction Puzzle, MC (30) 5. Mini Puzzles (35) 6. Lipids (35) 7. Puzzle (40) 8. Mechanisms (30) 9. Synthesis (30) Total (300) %

2 1. Nomenclature & Fundamentals (a) (9 points) Draw a simple example of each functional group below using skeletal structures (no other abbreviations such as R groups). Aldehyde Ester Ether (b) (8 points) The following compounds are arranged from most (left) to least (right) acidic. Fill in the pka values of each in the boxes provided. & Cl N N 3 C 4 (c) (12 points) Provide IUPAC names for any two following compounds. (2R,3E)-2-methoxy-5-oxo-3-hexenoic acid meta-bromoacetophenone (2R,6R)-2-tert-butyl-6-hydroxycyclohexanone Isopropyl cyclohexane carboxylate (d) (16 points) Complete the following Fischer, aworth projections and chair conformations β-d-galactopyranose (the C4 epimer of D-Glucose) FISCER: AWRT CAIR 1

3 2. Amino Acids & Peptides - The structures of L-proline, L-histidine, and L-glutamic acid at physiological p (7.4) are provided below, along with their pka s. Use these to complete parts (a) through (c) below. L-Proline (Pro, P) C 2 N 2 pka L-istidine (is, ) N N pka N C 2 pka pka L-Glutamic Acid (Glu, E) C 2 pka R N C 2 pka pka pka R 4.1 (a) (10 points) Titration of Glutamic Acid Draw the structure of the dominant ionic form of glutamic acid at each indicated p range. Indicate all charged atoms and circle those charges. Net Charge: p < < p < < p < 9.5 p > 9.5 (b) (15 points) Peptide Primary Structure - Draw the tripeptide containing L-Proline, L- Glutamic Acid, and L-istidine at p 1, where proline is the N-terminal and histidine is the C- terminal amino acid. Be sure to label all charged atoms where appropriate and indicate the overall net charge. (N-terminus) - Pro Glu is p 1 Net Charge (c) (10 points) What is the p range in which Pro-Glu-is tripeptide has a net charge of zero? Draw the structure of that net neutral peptide, labeling all charged atoms where appropriate. < p < 2

4 3. (20 points) Single Step Reactions Multiple Choice Circle the starting material(s) that would give the indicated product. More than one answer may be possible. (a) 1. PhMgBr (excess) C 3 Cl (b) Cl N 2 1. NaB Circle the correct product in each reaction. (c) C 3 1. LiAl 4 (excess) C 3 C 3 (d) N NC 3 NC 3 C 3 N NC 3 3 CN 3

5 4. (30 points) Reaction Puzzle Multiple Choice Fill in the best reagent for each transformation using the choices below. Simply put the letter in the box! ne letter per box, each letter may be used more than once, and not every letter needs to be used. Pro-tip: take it one reaction at a time and pay attention to the direction of the reaction arrow! N 2 N 2 CN Cl Br C 3 Br C 3 (A) Br 2, Ac (B) NaCN (C) N 3 (D) 1. LiAl 4 ; (E) 1. LiAl 4 ; 2. 2 (F) 1. NaB 4 ; (G) C 3, + () Excess C 3, + (I) SCl 2 (J) 3 + (K) 1. Ethylmagnesium bromide; (L) 1. N 3 ; 2. NaB 4 (M) 1. NaN 3, 2. LiAl 4, 3. 2 (N) 1. Cr 3, 3 + ; 2. SCl 2 4

6 5. (35 points) Mini-Puzzles. Fill in the missing molecules, paying close attention to the direction of the reaction arrow. (a) Show the products of two different reactions of α D-allopyranose. C 3 C 2 C 3 I (excess) 3 + α-d-allopyranose Ag 2 (b) Show the starting materials for two different methods for synthesizing istidine. 1. PBr 3, Br N N 1. N 3, + 3. Excess N N C 2 - istidine 2. NaB 4 (c) The two reactions below give the same product. Draw that product. NC Dess-Martin 1. C 3 MgBr Periodinane (d) Show the synthetic intermediate and reagents needed to synthesize the following ether. Br K C 3 5

7 6. Lipids (a) (15 points) Draw the triacylglycerol product of the following reaction. You are welcome to abbreviate the hydrocarbon chain from the fatty acid. What is the name of a very similar reaction performed with a carboxylic acid and alcohol under acidic conditions? (reaction name) (3 equiv.) (b) (20 points) The following phospholipid was subjected to saponification (basic hydrolysis). Draw the many products of the reaction. Be sure the reaction is balanced. P P N(C 3 ) 3 Excess Na 6

8 7. Carbohydrate Puzzle Read the following reaction descriptions carefully then draw the structures (Fischer projections) of monosaccharides A-F in the boxes provided. Compound A is a D-aldopentose that can be oxidized to an optically inactive aldaric acid B. n Kiliani-Fischer chain extension, A is converted to C and D. Compound C can be oxidized to an optically active aldaric acid E, but D is oxidized to an optically inactive aldaric acid F. What are the structures of A-F? A B N 3 (aq) Δ 1. CN 2. 2, Pd/C C D F + N 3 (aq) Δ N 3 (aq) Δ E 7

9 8. (30 points) Mechanisms Draw the full arrow-pushing mechanism for both reactions below, including all arrows for acid-base reactions. Include all intermediates with proper charges circled for each step. (a) 4,4-Dimethyl-1-cyclopentene carbaldehyde is made through a base-promoted intramolecular aldol cyclization of the dialdehyde below. Show this mechanism. Pro tip: consistently number the carbons in the starting material & product. Na Δ + 2 (b) (25 points) The first step in the Wohl degradation is the reaction of an aldopentose with hydroxylamine to form an oxime, which is closely related to an imine. Although we didn t cover this specific mechanism, students should be able to draw on knowledge from imine formation to carry out this mechanism. Draw the full arrow-pushing mechanism for the formation of the oxime, including reaction intermediates and charges clearly indicated, in the space below. Before you start, make a list of all bonds broken and formed in the boxes provided. bonds broken C 2 N 2 + N C bonds formed An xime 8

10 9. (30 points) Multi-Step Synthesis CSE TW Carry out the syntheses of the indicated target molecules using the starting material provided and any other reagents or carbon sources needed. Draw the product after each synthetic step. No mechanisms. (a) int on page 8! (b) 2 N Br (c) PUT A LARGE X VER TE ENTIRE REACTIN & SPACE YU ARE SKIPPING AND D NT WANT GRADED. TERWISE TE TP TW REACTINS WILL BE GRADED, EVEN IF TEY ARE BLANK! 9