Homework 4 - Answers - Homework Problem Set 4 Iverson...

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Unformatted text preview: Homework Problem Set 4 Iverson CH310N Due Wednesday, February 13 NAME (Print): _____________________________ SIGNATURE: _____________________________ Chemistry 310N Dr. Brent Iverson 4th Homework February 6, 2008 Please print the first three letters of your last name in the three boxes Homework Problem Set 4 Iverson CH310N Due Wednesday, February 13 Score: _________ Homework Problem Set 4 Iverson CH310N Due Wednesday, February 13 (3 or 5 pts each) Fill in the box with the product or products that are missing from the following chemical reaction equations. When a racemic mixture is formed, you must write "racemic" under both structures EVEN THOUGH YOU DREW BOTH STRUCTURES. Br 2 Li 2 Mg ether Li Br 1) P(Ph)3 2) nBuLi 1) 4 Li 2) Cu(I) CuLi P(Ph)3 MgBr 2 Br O OH O OH Cu Racemic H2SO4 (catalytic amount) + LiBr O HO H PCC H O O H Homework Problem Set 4 Iverson CH310N Due Wednesday, February 13 (3 or 5 pts each) Fill in the box with the product or products that are missing from the following chemical reaction equations. When a racemic mixture is formed, you must write "racemic" under both structures EVEN THOUGH YOU DREW BOTH STRUCTURES. OH 1) H 2) HCl / H 2O MgBr OH H Racemic 1) HO Na 2) HCl / H 2O OH OH catalytic H H Racemic OH H H O O O O H P(Ph)3 O MgBr OH MgBr 1) O 2) HCl / H 2O Racemic OH OH Homework Problem Set 4 Iverson CH310N Due Wednesday, February 13 (3 or 5 pts each) Fill in the box with the product or products that are missing from the following chemical reaction equations. When a racemic mixture is formed, you must write "racemic" under both structures EVEN THOUGH YOU DREW BOTH STRUCTURES. OH 1) O CH3 CH 3 OH racemic 2) HCl / H2O O C H OH 1) MgBr H 2) HCl / H2O 1) CO 2 2) HCl / H2O OH OH not chiral HCN P(Ph)3 O CN H3C C CH3 O H3C C CH 3 1) O H3C C CH 3 MgBr HO 2) HCl / H2O not chiral O + H2 O O O H3C C CH 3 HO H2SO4 OH Homework Problem Set 4 Iverson CH310N Due Wednesday, February 13 (18 pts.) Read these directions carefully. Read these directions carefully. (It was worth repeating) For the reaction shown below, fill in the details of the mechanism. Draw the appropriate chemical structures and draw arrows to show how pairs of electrons are moved to make and break bonds during the reaction of the 3-pentanone reacts with the ylide shown. Draw all non-bonded electrons as dots around the appropriate atoms and include all formal charges. Draw all products of each step and all products of the overall reaction. MAKE SURE TO FILL IN THE BLANK AT THE BOTTOM. Remember to draw arrows on this structure O O P(Ph)3 Intermediate A P(Ph)3 Remember to draw arrows on this structure O P(Ph)3 O P(Ph)3 All Products of overall reaction Intermediate B (2 pts) For the overall reaction, the "motive" is provided by formation of a type of bond that The bond drives the process to completion. What is that type of bond? _ ___ __ ___ __ ___O ___P ___ __ ___ __ _ __ __ Homework Problem Set 4 Iverson CH310N Due Wednesday, February 13 These are synthesis questions. You need to show how the starting material can be converted into the product(s) shown. You may use any reactions we have learned. Show all the reagents you need. Show each molecule synthesized along the way and be sure to pay attention to the regiochemistry and stereochemistry preferences for each reaction. (10 pts) All of the carbon atoms of the products must come from the starting material for this one! Recognize the product as a secondary alcohol, the Key Recognition Element of a Grignard reaction between an aldehyde and a Grignard reagent. H Racemic OH OH ? PCC PBr3 or HBr 1) Br O H HO H 2) HCl / H2O MgBr Mg ether The aldehyde can be made from the starting alcohol using PCC, and the Grignard reagent can be made from the corresponding alkyl halide derived from the starting alcohol. Note, the bromide was used, but it is also fine if you used the chloride derived from reaction with either SOCl 2 or HCl. Homework Problem Set 4 Iverson CH310N Due Wednesday, February 13 These are synthesis questions. You need to show how the starting material can be converted into the product(s) shown. You may use any reactions we have learned. Show all the reagents you need. Show each molecule synthesized along the way and be sure to pay attention to the regiochemistry and stereochemistry preferences for each reaction. (12 pts) All of the carbon atoms of the products must come from the starting material for this one! 2 HBr ? 1) O3 2) (CH3)S Br O O H P(Ph)3 n-BuLi H 2 2 P(Ph)3 2 P(Ph)3 Count carbons in the product (12) and realize that two molecules of the 3-carbon unit need to be added to one of the 6-carbon unit. Recognize that the last step makes alkenes in the locations required for carbon-carbon bond formation, indicating a Wittig reaction as the last step. Recognize that the ring can be opened to give the required dialdehyde by an ozonolysis. Recognize that the required Wittig ylide can be derived from the starting alkene via reaction with HBr (Markovnikov addition) followed by the unsual steps of adding P(Ph)3 followed by strong base (n-BuLi). H O O H2 SO4 OH * * OH racemic 2 Br 2 Mg ether 2 MgBr 1) H 2) HCl / H2O Alternative route: Above we have illustrated the most efficient synthetic route involving a Wittig reaction. A reasonable alterntive utilizes a Grignard reagent made from the same 2-bromopropane that is used to react with the same hexanedial to give a diol, that is then dehydrated in anhydrous acid (H2SO4) to give the product diene. This works because the desired product happens to be the so-called "Zaitsev" product favored in the dehydration reaction. This example underscores the idea that there are often more than one route to the synthesis of molecules, and we will accept any of these as long as they provide the desired product, based on the predominant products of each of the reactions you use along the way. ...
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This homework help was uploaded on 04/21/2008 for the course CH 310n taught by Professor Iverson during the Spring '08 term at University of Texas at Austin.

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