CHEMISTRY Statistics: 74 pts (74%) 94 pts (94%) 34 pts (34%) 26 (55%) 5 (11%)

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1 CEMISTRY MITERM # 1 answer key bruary 06, 2007 Statistics: Average: 74 pts (74%) ighest: 94 pts (94%) Lowest: 34 pts (34%) Number of students performing at or above average: 26 (55%) Number of students performing at or below 55%: 5 (11%) 1. (6 pts) Mark as true (T) or false (F) the following statements. o not explain! (F) All deactivating substituents are meta-directing; (F) The base peak in mass spectra is the peak with highest m/z ratio; (F) All electron-deficient species are observed in mass spectrometry; (T) rganometallic compounds are Lewis bases; (T) rganometallic compounds are ønsted bases; (T) Carbenes are electron-deficient; 2. Circle ALL that apply: A. (3 pts) The following reagents can be used in Friedel-Crafts reactions: a. Alkyl halides; b. Aryl halides; c. Acid chlorides; d. Alcohols; B. (3 pts) The following values are independent of the operating frequency of the NMR: a. Coupling constant; b. Gyromagnetic ratio; c. Chemical shift; d. Integral intensity; C. (3 pts) The following reactions lead to the conversion of a carbonyl group to a methylene group: a. emmensen reduction; b. Birch reduction; c. Wolff-Kishner reduction; d. Friedel-Crafts acylation; 3. (3 pts) Which pair of compounds will be most difficult to distinguish by MS: A. omocyclopentane and chlorocyclopentane; B. Cyclpentanol and cyclopentene; C. Cyclopentane and cyclopentene; 4. (4 pts) In each of the following pairs of compounds, indicate (circle) the compound, which will react faster with the indicated reagent. o not explain! A. Benzene or bromobenzene, with a mixture of nitric and sulfuric acid; B. Anisole or nitrobenzene, with isopropyl chloride and aluminum trichloride; C. Pyridine or pyrrole, with bromine and iron; or., with fuming sulfuric acid; 5. Write and complete a chemical equation for each of the following reactions: A. (3 pts) Thiophene + bromine, with iron catalyst; S 2 S

2 B. (3 pts) Naphthalene and sulfuric acid, upon heating; S 3 2 S 4 C. (3 pts) Acetophenone with Zn(g) alloy and ; Δ Zn(g) Δ. (3 pts) Phenylmagnesium bromide with benzaldehyde, followed by acidification; Mg 1) Ph /ether 2) 3 + E. (3 pts) Cyclopentene with diiodomethane, in the presence of Zn(Cu) alloy; C 2 I 2 Zn(Cu) 6. (24 pts) Indicate the principal organic product of each of the following reactions. If o-,p-mixture is expected, write both products. N 3 N S 4 2 N N 2 2 S 4 heat 2 N S 3 N 2 3 C 3 C Al 3 3 C 3 C C 3 2 C 3 C 3 2 S 4 C 3 N Sn 4 N N Zn (g) 2 NN 2 N K, heat Ph 1) Ph Na, liq. N 3 2) 3 + C 2 5 2) 3 + 1) 2 Mg /ether

3 I (C 3 C 2 ) 2 CuLi ether C 3 KC(C 3 ) 3 t-butanol 7. (4 pts) Provide formulas for the carbonyls of the following metals: A. Molybdenum (Mo); Mo(C) 6 B. Iron (); (C) 5 8. (3 pts) Suggest a suitable combination of organometallic compound and a carbonyl compound (aldehyde or ketone) that could be used to generate the following alcohol: More than one combination is possible. ere is one: + Mg 9. (4 pts) Identify the reagents in the following scheme: Al 3 Zn(g) Suggest a detailed synthetic sequence for the preparation of each of the following molecules, starting from the indicated compound, and using any other necessary reagents (For convenience, assume that you can separate o- and p-isomers): A. (4 pts) 3,5-dibromoethylbenzene, using benzene as a starting material; Al Zn(g) B. (4 pts) Methylcyclopropane, using acetaldehyde ( 3C C ) as a starting material; 1) C 3 Mg / ether 2) P 4 Δ C 2 I 2 Zn(Cu) C. (4 pts) 2,7-imethyloctane, from 1-bromo-3-methylbutane as the only source of carbon atoms; 1) 4Li / ether 2 2) CuI CuLi 2 1) 2) 3 +

4 11. (4 pts) Suggest a detailed mechanism for the following reaction. Al 3 + Al 3 + Al 4 Al Al (4 pts) Certain compound A has molecular formula C and is generated by Friedel-Crafts acylation. It undergoes emmensen reduction to yield compound B. The 1 NMR spectrum of A is shown below. Its broad-band decoupled 13 C NMR spectrum shows signals at 211.0, 142.1, 138.4, 133.7, 129.3, 71.8, Propose structures for A and B Solution: The compound has e.u. = 5. From the 1 NMR spectrum one can deduce the presence of a p-disubstituted benzene ring (e.u. = 4). In addition, compound A is generated via Friedel Crafts acylation, and should therefore be an aryl ketone, i.e. it has a ketone carbonyl group (e.u. = 1). The latter conclusion is also supported by the 13 C NMR, which shows a signal at ppm, in a region where only ketone carbonyl groups appear. The two singlets upfield are for 3 each and most likely correspond to two C 3 groups. The one at δ ~ 2.3 ppm is either attached to a benzene ring or a carbonyl group. The C 3 at δ ~ 3.9 ppm is likely attached to oxygen (also supported by the 13 C NMR, which shows a signal at 71.8 ppm). All this information leads to the following structure for A: 3 C Compound A Compound B is prepared from A via emmensen reduction. It has the following structure: 3 C Zn(g) 3 C Compound A Compound B

5 13. (4 pts) Following are three compounds and their 1 NMR spectra. Assign each compound its correct spectrum and assign all signals to their corresponding hydrogens. A B C B C A

6 14. (4 pts) Propylbenzene and isopropylbenzene are constitutional isomers. ne of these compounds has a mass spectrum with prominent peaks at m/z 120 and 105 (Spectrum A). The other has a mass spectrum with prominent peaks at m/z 120 and 91 (Spectrum B). Which compound has which spectrum? Solution: Both structures are alkylbenzenes and in either case the predominant fragmentation is the formation of a benzylic carbocation. In the case of propylbenzene the cation is generated by detachment of an ethyl radical and has an m/z = 91 (Spectrum B). In the case of isopropylbenzene the benzylic carbocation is generated by detachment of a methyl radical and has an m/z = 105 (Spectrum A). C 2 + C 3 C 2 M +, m/z = 120 m/z = 91 + C 3 M +, m/z = 120 m/z = (3 pts) BNUS PRBLEM (In order to receive credit for this problem, it has to be solved entirely!!). In the Gatterman Koch formylation, an aldehyde group is introduced directly into the benzene ring. It involves a reaction of the aromatic compound with carbon monoxide (C) and in the presence of catalyst, as shown in the example below for toluene. Propose a detailed mechanism for this conversion (int: Recall from class discussion the Lewis structure of C). C 3 C 3 + C catalyst C C C the electrophile in the Gatterman - Koch formylation C + C + C 3 C 3 C 3 + C C C