2005spring-finalexamasolns

2005spring-finalexamasolns - Chemistry 140C (Tor) Spring...

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Unformatted text preview: Chemistry 140C (Tor) Spring 2005 Final Exam (V.1) This exam accounts for 50% of the final grade. Time 7:00 10:00 PM. Mark your final answer clearly and completely erase irrelevant information! Remember: Exams written in pencil will not be regraded! Additional pages are at the end for your convenience. Please indicate if your final answer should be found at the end of the exam. Good Luck! Your Name (Please Print): Your ID # : KEY _____________________________ Question # 1: ..................................................................... /20 Question # 2: ..................................................................... /32 Question # 3: ..................................................................... /80 Question # 4: ..................................................................... /32 Question # 5: ..................................................................... /08 Question # 6: ..................................................................... /34 Question # 7: ..................................................................... /16 Question # 8: ..................................................................... /30 Question # 9: ..................................................................... /12 Question # 10:................................................................... /12 Question # 11:................................................................... /08 Question # 12:................................................................... /16 Total................................................................................... /300 1 Name: ________________________ ID# _________________ 06-08-05 1. Treatment of the compound 1 with aqueous base gives the diketone 2: O HO! H2O O O O 1 2 O Write a detailed, arrow-pushing, stepwise mechanism that accounts for this transformation. !!!Note: Show all intermediates! Transfer H's intermolecularly! Two processes take place: 1. Base-mediated hydrolysis of the ester 2. Retro aldol reaction H O O O O H O O O O HO! O O OH O O O H O Also acceptable: O H O O O OH O 4 key steps, 5 points each = 20 points 2 Name: ________________________ ID# _________________ 06-08-05 2. Treatment of ketoester 3 with sodium ethoxide in ethanol, followed by a reaction with ethyl iodide gives ketoester 4: O Me O OEt EtO!Na+ EtOH 3 4 CH3CH2I Me O Et O OEt Write a detailed stepwise mechanism that accounts for the formation of 4. Two processes take place: 1. Ethoxide-mediated retro-Claisen (Dieckmann) reaction 2. Dieckmann reaction followed by alkylation of the enolate O Me O OEt EtO! 3 EtO! O EtO H O Me H OEt EtO O Me O OEt rotate structure EtO O Me O OEt EtO O Me O OEt H O Et O Me OEt O OEt EtO! O Me H O OEt Me O O OEt I Me O Et O OEt 4 8 key steps, 4 points each = 32 points 3 Name: ________________________ ID# _________________ 06-08-05 3. For each one of the following reactions, circle the product that is formed. 5 points each (a) O MeO!Na+, MeOH, 25 oC Br O O O O (b) O N Li THF, ! 78 oC Br O O O O (c) O H3O+, H2O O O O (d) MeO O O 1. MeO!Na+, MeOH 2. H3O+ O O O O O O 4 Name: ________________________ ID# _________________ 06-08-05 (e) H3CO O O 1. CH3O!Na+, CH3OH OCH3 2. H3O+, H2O O O OCH3 O O OCH3 O O OCH3 O O OCH3 (f) O EtO O OEt 1. EtO!Na+, EtOH 2. CH3CH2Br 3. HCl, H2O, " O HO O HO O HO O (g) O 1. EtO!Na+, EtOH 2. NaOH, H2O, " O O O O O O O O O O 5 Name: ________________________ ID# _________________ 06-08-05 O (h) O O O HO O OH HO O O OH HO O O O OH OH CN H3O+, H2O, ! (i) O OCH3 excess CH3CH2OH, H+ O O O O OCH3 OH O OCH2CH3 O OCH2CH3 O OH O O OH O (j) H2N O NH2 O O O O O t-BuOH, Et3N O O N H O H N O O O H2N H N O O O O N H O NH2 H2N O H N O 6 Name: ________________________ ID# _________________ 06-08-05 Br (k) 1. NaCN, DMSO 2. HCl, H2O, " OH O O OH OH O O OH (l) EtO O O O OEt N O 1. EtO!Na+, EtOH 2. O OEt 3. HCl, H2O, " O O Cl H3N OEt O O OH OH OH Cl H3N OH Cl H3N O O OH O OH Cl H3N O OH (m) MeO O O HO O N H NH2 HN N H O NH2 " O HN NH O O HN O O O N O 7 Name: ________________________ O O HO O O O O H O O OH ID# _________________ 06-08-05 (n) H3O+ O O O H O H O O (o) O OH NH2 DCC, THF NH O NH O NH (p) N H O NH2 1. Ph!N=C=S 2. dil H3O+ O Ph N NH Ph N S N Ph N S NH Ph N S NH S O O O 8 Name: ________________________ ID# _________________ 06-08-05 4. For each of the following pairs of compounds, decide which one is more acidic, and indicate it by using the symbol ">" (e.g., A>B for "A is more acidic than B"). ! Note: the H to be considered is highlighted. " 4 points each A O (a) B O < H H O (b) N H O < H O H O OH NH3+ O (c) > OH (d) O H O OCH3 < O H O H N (e) H > N NH3 (f) NH3 > O N N H (g) < N N H O O Me N (h) H Me > N H H H 9 Name: ________________________ ID# _________________ 06-08-05 5. Cimetidine (Tagamet) is a prescribed drug for the control of gastric acidity. H N N S N N H H2N H Cimetidine Arginine N CN CH3 HO2C H N N N H H H (a) A cyano-modified guanidine group is present in cimetidine. Do you expect this guanidine group to be more basic or less basic than the guanidine group in arginine? More basic Less basic 4 points (b) Rank the basicity of the two nitrogens in the heterocyclic ring (1 being more basic than 2). Show your ranking on the structure below: 4 points S 2 H N N1 10 Name: ________________________ ID# _________________ 06-08-05 6. Solanine, a poisonous glyco-alkaloid, is found in potatoes (particularly in new green areas of the skin and fresh sprouts). N OH HO HO O HO HO HO OH O HO OH O O O ! ! O " Solanine (a) Is solanine a reducing or non-reducing carbohydrate derivative? 2 points !"#$%&'())) '*'+!"#$%&'() (b) Identify all glycosidic linkages in solanine and classify them as ! or ". Mark your answer on the structure shown above Note: no points were taken for mistakes regarding the ! glycosidic bond 3 # 2 = 6 (c) Show the structures of all products obtained when solanine is hydrolyzed in aqueous acid. 4 # 4 points = 16 !H H! H! ! H! H! H! !H !H !H H! H! !H ! !H ! H! !H N H 11 Name: ________________________ ID# _________________ 06-08-05 (d) One of the monosaccharides in solanine belongs to the L-family of monosaccharides. Circle this L-monosaccharide on the structure given below. 4 points N OH HO HO O HO HO HO OH O HO O O OH O O (e) The aglycon of solanine is called solanidine. N HO Solanidine Three cycles of the Hofmann procedure (exhaustive methylation/elimination) are required to remove the nitrogen from this molecule in the form of (CH3)3N. Several possible isomeric alkenes can be formed. Show the structures of TWO possible end products of this process. !" !" Any 2 out of these 4 are acceptable 2 x 3 points = 6 !" !" 12 Name: ________________________ ID# _________________ 06-08-05 7. Treatment of adenosine with strong aqueous acid may cause depurination as shown below: NH2 N HO O N N N NH2 H3O+'(H2O HO O OH H N N N N OH OH Write a detailed, arrow-pushing, stepwise mechanism that accounts for this transformation. H H ! H #H$ # H! ! # # # H! ! !H !H !H H! ! ! H !H H H H %&'()*++,-.*/&,0 H # # #H$ # # H ! # H # #H$ H! ! H # # H! H ! !H !H ! H H H # # # #H$ # (10 ! H ! H # #H$ # # H! ! H # # #H$ # # H! ! H! ! # !H !H !H 4 key steps = 4 x 5 pnts = 20 13 Name: ________________________ ID# _________________ 06-08-05 8. To elucidate the sequence of an octapeptide, the following experiments were conducted: Complete hydrolysis (6N HCl, 110 C, 24 hours) followed by amino acid analysis indicated a ratio of: Ala (1), Asp (2), Gly (1), Leu (1), Lys (1), Tyr (1) and Val (1). Treatment of the octapeptide with 1-fluoro-2,4-dinitrobenzene followed by 6N HCl hydrolysis produced N-(2,4-dinitrophenyl)aspartic acid together with free Asp, Gly, Leu, Ala, Val, and Tyr as well as !-N-(2,4-dinitrophenyl)lysine. Incomplete acid hydrolysis caused random cleavage of many octapeptide molecules into an assortment of peptide fragments that included (among other fragments not shown): AlaTyr, AspGly, LeuAla and AlaTyrVal. Treatment with trypsin (an enzyme that cleaves the amide bond at the carboxy end of amino acids that contain a positively charged residue: Lys and Arg) cleaved the peptide only once, giving two fragments: a pentapeptide and a tripeptide. Treatment with chymotrypsin (an enzyme that cleaves the amide bond at the carboxy end of amino acids that contain an aromatic residue: Phe, Tyr and Trp) cleaved the peptide only once, giving two fragments: a hexapeptide and a dipeptide. a) Deduce the amino acid sequence of the octapeptide. (Clearly mark the N-terminal and the C-terminal amino acids). 14 points N b) Asp Gly Lys Leu Ala Tyr Val Asp C What would be the net charge of the octapeptide at pH 1? 4 points (Note: The structures of the amino acids' side-chains are given below) +2 c) What would be the net charge of the octapeptide at pH 7? 1 4 points d) What would be the net charge of the octapeptide at pH 12? 4 4 points e) Would the pI of the octapeptide be above pH 7 or below pH 7? (Circle your answer.) pI<7 Or: pI>7 4 points The side-chains of the various amino acids: !"# "#CH3 !$% "#CH2COOH ,#" "#CH(CH3)2 &"' "#H CH2 ,-. /01/ OH )*+ "#CH2CH(CH3)2 )'$ "#CH2CH2CH2CH2NH2 -'. "# 14 Name: ________________________ ID# _________________ 06-08-05 9. When glutamic acid 5 is treated with nitrous acid, a molecule of dinitrogen (N2) is lost and the lactone 6 is formed: O HO NH2 O OH HNO2, H2O '!( )C O HO O N2 5 6 O Provide a mechanistic explanation by showing all key intermediate of this transformation that account for the formation of this product (pay attention to stereochemistry). $ "$ !"# $ $" "!$#% "#$ ' ! ( )* $ "$ $ $ !# +!,$ $ -./ 0!1.23.4051.67 $ !# $ $" "$ $ $ " "#$ "$ !# Two essential steps: 1. Formation of a diazonium ion from the primary amine and nitrous acid 2. Nucleophilic substitution reaction where N2 is the leaving group and the carboxylic acid serves as a nucleophile (note the inversion of configuration!) 15 Name: ________________________ ID# _________________ 06-08-05 10. Ascorbic acid (vitamin C) cannot be biosynthesized by humans and we must obtain it through our diet (it is enzymatically synthesized from glucose by many plants). Although it does not have a carboxylic group, it is a rather acidic compound with a pKa of 4.17 (lower than that of acetic acid, pKa 4.75)! CH2OH H OH O O HO OH Ascorbic acid (a) Identify the most acidic group in ascorbic acid and mark it on the structure shown above. (b) Provide an explanation (preferably with one sentence and one structure) for the unusual acidity of this compound. Note the high stability of the deprotonated form, due to the extended conjugation of the conjugate base (negative charge is mainly delocalized over the two electronegative oxygens): #"$!" " !" ! " ! "$! #"$!" !" ! ! "&!' "! !" ! !" #"$!" " !" ! ! ! !" 16 Name: ________________________ ID# _________________ 06-08-05 11. A researcher isolated a monosaccharide with a molecular weight of 150. Surprisingly, this monosaccharide was not optically active. Propose a structure for this monosaccharide. The general formula of any monosaccharide is Cn(H2O)n. This indicates that each "unit" should have a MW of 12n(18)n which is 30n. Since the MW is 150, this indicates the carbohydrate is a pentose! (150:30=5 carbons) Since the monosaccharide is optically inactive, it must be a meso derivative! Possible structures are: CH2OH H OH O H OH CH2OH = OH HO O HO OH CH2OH HO H O HO H CH2OH = OH HO O HO OH 17 Name: ________________________ ID# _________________ 06-08-05 12. Shown below are two pteridines called 6MAP and 6MI, studied as purine analogs by Dr. Mary Hawkins at the National Cancer Institute: NH2 N O N ! N N O N N ! N O N H !$ NH2 HO HO O "#%& "#$ (a) One of the analogs shown above can form a base pair with C that is analogous to a Watson-Crick (WC) pairing. Select this analog and write the most favorable WClike base pair formed. 8 points H N O N R N N H H O N H N N R O H N 6MI C (b) Write a tautomer of 6MI that can form a WC-like base pair with T. 8 points ! " ! ) ! " ! $ " ! ) ! " ! ! ! $ $ " $ ! ! ! $ $ $ " # !"I$%&'( !"I$%&'( * H H 3C O $ $ % O H H $ $ $ $ $ % % $ H $ $ O H H H O $ $ $ H $ $ % " ! 18 # $ ...
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This note was uploaded on 06/07/2008 for the course CHEM 140C taught by Professor Nefzi during the Spring '06 term at UCSD.

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