CHEMISTRY 314-01 MIDTERM # 2 – answer key October 28, 2008
Statistics: • Average: 55 pts (55%); • Highest: 88 pts (88%); Lowest: 31 pts (31%) • Number of students performing at or above average: 6 (43%)
1. (6 pts) Mark as true (T) or false (F) the following statements. Do not explain! • (T) Thiols are more acidic than water; • (T) Ethers are Brønsted bases and Lewis bases; • (F) Acetals decompose only in basic conditions; • (T) Aldehydes are more reactive than ketones in nucleophilic addition reactions; • (T) Acetals are formed only in the presence of acid catalyst; • (T) The haloform reaction requires basic conditions;
2. Circle ALL that apply: A. (2 pts) The following reactions can be used to prepare aldehydes: a. Oxidation of secondary alcohols with PCC; b. Reaction of vicinal diols with periodic acid; c. Oxidation of primary alcohols with potassium permanganate; d. Reaction of esters with Grignard reagents, followed by acid; B. (2 pts) The following reactions occur through an addition – elimination mechanism: a. Formation of hemiacetals; b. Formation of oximes; c. Formation of hydrates; d. The Wittig reaction; C. (2 pts) Hemiacetals are: a. Decomposed to carbonyl compounds in acidic conditions; b. Decomposed to carbonyl compounds in basic conditions; c. Converted to acetals in acidic conditions; d. Converted to acetals in basic conditions;
3. (5 pts) Provide an acceptable name for each of the following compounds:
OH SO H O OH 3 S OH O phenol cis-1,2-cyclohexanediol benzenesulfonic acid 1,4-dioxane thiolane
4. (5 pts) Provide the correct structure, matching each of the following names:
O
CHO O HO CN O O H
methyl vinyl ketone cyclopentanecarbaldehyde 3-oxopentanal benzophenone acetone cyanohydrin
5. (3 pts) Among the following structures, select those that cannot undergo aldol self-condensation: O O O O H H
6. (7 pts) Suggest the reagents necessary to conduct the following transformations:
OH
H2O/ 1) CH3MgBr + + H3O 2) H3O
O HO OsO4 HO O HIO4 1) BH3.THF PCC/ OH t-BuOOH - OH-, t-BuOH 2) H2O2, OH CH2Cl2
start 7. (36 pts) Write the principal organic product of each of the following reactions: O OH OsO4 K2Cr2O7 OH OH t-BuOOH OH H2SO4 - t-BuOH, OH
OH O H PCC NaIO O OH 4 O CH2Cl2 OH H
NaBH O O 4 3 Br2 - + CHBr ethanol NaOH O 3 O OH O OH HO CN CH3COOOH 1. NaCN OH H2O 2. HCl
O O Br O O OH OH OH NaOH p-TsOH benzene heat O O K2Cr2O7 O MCPBA
H H SO OH CH2Cl2 O 2 4 O
Ph 1) Ph3P KOH 2) n-BuLi/THF + PhCHO I Ph CHO C2H5OH Ph CHO 3) O
O O H H O+ N + 3 NaOCH3 N H3C CH3 CH3OH O O 8. Write the complete equation for each of the following reactions: a. (2 pts) Diethyl ether and HI; HI O 2 I
b. (2 pts) 2-Chlorobenzaldehyde and hydroxylamine, catalyzed by acid; OH O N + H H3O H + NH2OH Cl Cl
c. (2 pts) Acetaldehyde and ethylene glycol, catalyzed by acid; O + O H3O O + HO OH H3C H H3C H
8. (4 pts) Hydroxyaldehydes readily react to form cyclic hemiacetals. Suggest a detailed mechanism for the following conversion (Structures and equations please, no verbal explanations!).
O + H3O HO H O OH H O O + H O H2O 3 + HO H HO H + H3O O OH O OH H
9. (2 pts) Suggest appropriate starting materials for the preparation of the following compound via the Williamson ether synthesis:
Na+ O Br + -O
9. (4 pts) Suggest a suitable set of starting materials to prepare each of the following compounds in a single step, using the aldol condensation.
O O CH3 CH3 O O + O O
10. (3 pts) Suggest a sequence, using protection – deprotection, that would enable you to conduct the following transformation:
O OH O ?? Br O + H H
OH O O + HO OH O O 1) Mg/ether 3) H3O Br Br H H TsOH H benzene, Δ 2) O
12. Suggest a plausible synthetic sequence for the preparation of each of the following compounds. H O
?? 1-phenyl-1,2-ethanediol A. (4 pts) . Use any necessary organic or inorganic agents.
OH H O H3C OH OH 1. CH3MgBr/ether 2. H O+ 3 H2SO4 OsO4 heat t-BuOOH, - OH , t-BuOH
?? OH O B. (4 pts) O Use ethanol as the only source of carbon atoms. Use any other necessary organic or inorganic reagents. H PCC OH O CH Cl 2 2 TsOH O OsO 4 benzene O H2SO4 t-BuOOH OH H CCH HO OH Δ heat 2 2 - OH , t-BuOH
13. (5 pts) Certain ester, upon reaction with a Grignard reagent, followed by acid, yields compound A whose 1H and 13C NMR are shown below. Compound A has molecular formula C12H18O. A. Deduce the structure of A. B. Propose the structure of the starting ester.
Compound A: OH
CH3 CH3 6
H3CCH3
1
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
140 130 120 110 100 90 80 70 60 50 40 30 20 10
The starting material can be any ester of the general formula:
O
OR
H3CCH3 , where R could be CH3, C2H5, etc.
14. (3 pts) BONUS PROBLEM (In order to receive credit for this problem, it has to be solved entirely!!). The so-called sulfur ylides are also very useful synthetically. They react with ketones to form epoxides. Suggest a detailed mechanism for the reaction below.
O O
+ H2CS(CH3)2 + (CH3)2S
O O O S(CH3)2
+ H2CS(CH3)2 + (CH3)2S