CAPTER 12 W: REDX REACTINS XIDATIN STATES AND GENERAL CNCEPTS 1. Are the following statements true or false? When a carbon atom changes its oxidation state from -2 to 0 it is reduce The oxidation state of carbon in methane is -4. When a carbon atom gains hydrogen (is connected to more hydrogen atoms than before), it is reduce The S N 2 reaction C 3 Br + à C 3 + Br is NT a redox reaction. 2. Calculate the oxidation state for each atom in the transformations below. Then identify whether the organic compound in each process is oxidized, reduced, or not undergoing a redox reaction. C C Br 3. Identify if each process below is a reduction, oxidation, or neither (not a redox reaction). Process Rxn Type Process Br Rxn Type Page 1
YDRGENATIN 4. Draw the two enantiomeric products formed in this reaction, then explain why a racemic mixture is produce 2 5. Explain why reactions A + C make only or mainly one product, while reaction B makes two products. A C B 6. Give the major organic product of each reaction, paying attention to stereochemistry. Indicate if a racemic mixture is expecte excess 2 e. excess 2 2 f. Pt (cat.) excess 2 g. Pt (cat.) Pt (cat.) h. Page 2
7. Structures A-C are constitutional isomers of C 8 14. Propose a possible structure for A-C that fits each of the observations below. Structure A reacts completely with 2 moles of 2 (w/ Pd catalyst). Structure B reacts completely with 1 mole of 2 (w/ Pd catalyst). Structure C does not react with 2 /P 8. (Multiple choice) Which statement is false about the platinum used in a hydrogenation reaction? The platinum is regenerated after the reaction. The platinum changes oxidation state during the course of the reaction. The platinum lowers the activation barrier for the reaction between alkene and 2. ne mole of platinum must be used for every mole of alkene to fully hydrogenate the alkene. mcpba XIDATIN 9. Give the major organic product of each reaction, paying attention to stereochemistry. Indicate if a racemic mixture is expecte mcpba mcpba C CNa +, 2 mcpba Na +, 2 mcpba +, C 3 10. (Multiple choice) Which compound A-D is most likely to react in a similar way to mcpba? (int: what is the reactive part of the mcpba reagent?) Cl A B C D Page 3
s 4 XIDATIN 11. Give the major organic product of each reaction, paying attention to stereochemistry. Indicate if a racemic mixture is expecte cat. s 4 NM, 2 s 4, NM, 2 excess Na C 3 C 2 Br cat. s 4 NM, 2 s 4, NM, 2 excess PBr 3 12. (Multiple choice) The function of NM in the reaction between an alkene and osmium tetroxide is to: Block one face of the alkene so the oxygen atoms add to the same face. xidize the osmium intermediate to regenerate the s 4. Lower the activation barrier between the alkene and the s 4. To prepare the osmium surface for the alkene. ZNLYSIS 13. Give all organic products of these reactions. 3 C 3 SC 3 3 Zn, 2 3 3 Zn, 2 S(C 3 ) 2 Page 4
14. For each problem, propose a structure that upon ozonolysis would yield only the products shown. 3 Zn, 2 + 3 Zn, 2 + 3 Zn, 2 3 Zn, 2 15. Propose structures for A-D in the scheme below. Unknown A (with molecular formula C 10 18 ) reacts with concentrated 2 S 4 to form a mixture of two compounds (B +C, both with a molecular formula of C 10 16 ). B + C both react with 2 in the presence of a Pd catalyst to form decalin. zonolysis of B produces E and ozonolysis of C produces diketone D with a molecular formula of C 10 16 2. A B C con. 2 S 4 heat + C 10 18 C 10 16 C 10 16 3 Zn 2 2 3 Zn decalin decalin D E diketone, C 10 16 2 Page 5
CRMIUM XIDATINS 16. Give the major organic product of each reaction. Assume sufficient chromium reagent (excess) for complete reaction of the organic compoun Cr 3 2 S 4 (aq) f. C 2 Cl 2 Na 2 Cr 2 7 2 S 4 (aq) g. C 2 Cl 2 Cr 3 2 S 4 (aq) h. Na 2 Cr 2 7 2 S 4 (aq) K 2 Cr 2 7 2 S 4 (aq) i. C 2 Cl 2 e. C 2 Cl 2 j. Cr 3 2 S 4 (aq) 17. For each problem, draw a structure that matches each set of criteri Criteria Possible Structure as a molecular formula of C 5 10 Reacts with Cr 3 / 2 S 4 to produce a blue-green precipitate Reacts with 2 in the presence of a Pd catalyst as a molecular formula of C 5 10 Reacts with Cr 3 / 2 S 4 to produce a blue-green precipitate Does not react with 2 in the presence of a Pd catalyst as a molecular formula of C 6 12 When Cr 3 / 2 S 4 is added, an orange solution is observed When Br 2 is added, the solution turns colorless Page 6
18. (Multiple choice) The reason a primary alcohol is oxidized to a carboxylic acid with Cr 3 / 2 S 4, but to an aldehyde with /C 2 Cl 2 is: There are not enough oxygen atoms in the reagent. is not a strong enough oxidizing agent to react with alcohols. The Cr 3 reagent is in an aqueous solvent while the reagent is not. The Cr 3 reagent is acidic, which helps the to leave. SUMMARY F REDX REACTINS 19. For each reaction, decide whether the organic compound is undergoing a reduction, oxidation, or neither (is not undergoing a redox reaction). Reaction RCl rxn with Na R rxn with Br Red, x or neither Reaction Red, x or neither Alkene rxn with mcpba Alkene rxn with 2 / Pd R rxn with Cr 3 / 2 S 4 Alkene rxn with Cl Alkene rxn with s 4 / NM, 2 20. Give the major organic product of each reaction. Indicate if a racemic mixture is produce Cr 3 C 3 2 S 4 (aq) C 3 Pt cat. 3 e. Zn, 2 mcpba +, C 3 s 4 cat. NM, 2 f. C 2 Cl 2 Page 7