(CHE 325) Organic Chemistry II Spring 2011 EXAM #1

Size: px

Start display at page:

Download "(CHE 325) Organic Chemistry II Spring 2011 EXAM #1"

Vivian Shaw
7 years ago
Views:

1 (CE 325) rganic Chemistry II Spring 2011 EXAM #1 Name: KEY ID#: Check your exam to be sure it is complete. There are nine questions in this exam. It is worth 100 points. To receive full credit for your submissions, make sure you do your own work. Read each question carefully, and answer in clearly legible and coherent English. Use the back of the page for additional space if needed. Partial credit will be given, so show your work. Don't fall in love with individual problems. Do the ones first which you can do easily. Pace yourself. Good luck! N. Totah 1. (of 6) 2. (of 6) 3. (of 8) 4. (of 14) 5. (of 12) 6. (of 12) 7. (of 20) 8. (of 12) 9. (of 10) Total: (100)

2 1. (6 points) Give IUPAC names for the following compounds: a. Br o-bromonitrobenzene b. N 2 C 2 3 2,6-dichloro-4-ethylaniline 2. (6 points) Write a complete, stepwise mechanism for the following transformation. Use curved arrows to denote electron flow. + 2 S 4 2 or S 4 2

3 3a. (6 points) Consider the compounds below: * C3 C 2 C A B i. ow many signals would you expect to see in the 1 NMR spectrum of compound A? Answer: two ii. What is the relationship between the two protons marked with an asterisk (*) in compound A? (circle one) different homotopic enantiotopic diastereotopic iii. The 13 C NMR spectrum of compound B shows five signals. ow many signals in the corresponding DEPT-135 spectrum would point up? Answer: four 3b. (2 points) What is the most likely structure of the molecule that gave the following 1 NMR spectrum? Circle your answer. C D E F 3

4 4a. (8 points) Label the following structures as aromatic, antiaromatic, or nonaromatic. N N nonaromatic antiaromatic aromatic aromatic 4b. (6 points) Which of the following hydrocarbons (A or B) would you expect to be deprotonated most readily in the presence of a base? Briefly explain. For full credit, you will need to discuss both compounds. A B Compound B is expected to be more acidic. In compound A, loss of a proton results in formation of an unstable antiaromatic compound (8π electrons; cycloheptatrienyl anion). owever, deprotonation of compound B results in formation of an stable, aromatic system (6π electrons; cyclopentadienyl anion). Due to the stability associatied with aromaticity, compound B should thus be deprotonated more readily (e.g. is more acidic). 4

5 5a. (4 points) Rank the following compounds in order of decreasing reactivity to Electrophilic Aromatic Substitution. Rank the most reactive compound 1, and the least reactive compound 4. Place the number corresponding to the relative reactivity of each compound in the blank below it. As( ) 3 S b. (4 points) Rank the following compounds in order of decreasing reactivity to Nucleophilic Aromatic Substitution. Rank the most reactive compound 1, and the least reactive compound 4. Place the number corresponding to the relative reactivity of each compound in the blank below it c. (4 points) Trifluoromethylbenzene undergoes Electrophilic Aromatic Substitution. Do you expect this compound to react faster or more slowly than benzene under identical reaction conditions (e.g. is the -CF 3 group activating or deactivating)? Briefly explain your reasoning. CF 3 trifluoromethylbenzene Trifluoromethylbenzene will react more slowly than benzene (CF 3 is deactivating. The CF 3 group withdraws electron density from the ring by induction making the ring a poorer nucleophile. 5

6 6. (12 points) Match each of the compounds A, B, and C with the appropriate broad band decoupled 13 C NMR spectra shown below. Briefly explain your reasoning. Note: for full credit, you rationale must unambiguousely exclude the other two compounds. Cite chemical shifts and identify relevant functionality in your discussion. Be specific. A B C 13 C NMR spectra: i. Compound: B TMS ppm Reasoning: as a C= peak (ca. 180 ppm) Does not show peak at ca. 60ppm (C- linkage) 6

7 ii. Compound: C TMS ppm Reasoning: has no C= at ca. 180ppm or shows C=C peaks ca ppm iii. Compound: A TMS ppm Reasoning: shows both C= (180 ppm) and C- (60ppm) peaks 7

8 7. (20 points) Predict the major product(s) for the following reactions. Assume reagents are present in equimolar amounts unless otherwise indicated. early depict any stereochemistry. "No Reaction" is a possible answer. CAUTIN! Don't confuse reactions that will occur slowly with those that will not occur! a. N 3 2 N 2 S 4 2 N b. Al 3 c. Me 3 N I 2 Cu 2 Me 3 N I d. S 3 1. Na, 300 C

9 e. S 3 2 S 4 3 S + S 3 f. Br C 2 Br 2 FeBr 3 C 2 2 N 2 N C 2 Br 2 N g. KMn 4 (excess) 2 C 2 (step 1) C 2 product(s) of step 1 Al 3 (step 2) No Reaction h. NBS C 4, (PhC) 2 Br 9

10 8. (12 points) Propose a structure that is consistent with the spectral data provided. For full credit, show your work and briefly explain your reasoning. As part of your answer, clearly correlate each peak in the 1 NMR spectrum to the structure of your compound (e.g. label the peaks). F.W.: C IR: 740 cm -1 1 NMR: integral values are listed above each peak 3 4 a a a a c b d e b a 3 c 2 d 2 e ppm IR suggests this is a 1,2-disubstituted benzene NMR supports structure as per labelled peaks 10

11 9. (10 points) Show how you would synthesize the following compounds from benzene or toluene. Use any other organic or inorganic reagents required. Avoid product mixtures if possible, but assume that ortho and para products can be separated. early indicate at what stage (if any) such separations are needed. a. N 2 N 3 2 S 4 + (separate) 1. Fe, Na N 2 2 Fe 3 N 2 or 2,Pd b. S 3 Al 3 S 3 2 Pd/C S 3 2 S 4 (+ ortho) 11

CHEM 211 CHAPTER 16 - Homework

CHEM 211 CHAPTER 16 - Homework SHORT ANSWER Consider the Friedel-Crafts alkylation reaction below to answer the following question(s): 1. Refer to the reaction above. Draw the structure of the electrophilic