322af01_e3_key - CHEMISTRY 322aL/325aL Please K W EXAM NO 3...

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Unformatted text preview: CHEMISTRY 322aL/325aL Please K W EXAM NO. 3 Print Last Name OCTOBER 31, 2001 - First Name SSN TA's Name Grader (1) (15') __ (2) (15) __ _ (3) (20) __ _ (4) (10) ____ __ (5) (10) __ _ (6) (15) __ __ (7) (15) __ __ (100) Lab Day 8: Time first letter of last name I will observe all the rules of Academic Integrity while taking this exam. Chemistry 322a / 325a /2—/ Name Exam No. 3 (1) (15) Complete the chemical reactions below by providing the missing organic product within each box. You do not need to show the byproducts of the reactions, or any mechanisms. Be careful to show stereochemical details in the products wherever they are important. '"“ (EH3 H""' excess H (A) /C\c ECH 2 CH3CH2 Pt, ethanol optically active cHZCHZCH3 CH u" H20 (B) é/C\ Br acetone CH3CH2 single enantiomer (optical y a ive f. ~ ' W ‘L- \ t K H3 + (C) Hun-clC Na 1 / CHZCHzBr aceto itrile - L :? C6H5 single enantiomer J awn. M B .... FH2CH3 NaOCHZCHa (D) r \ H CH3 ethanol single enantiomer (E) (CH3)2CH C9H180 (single diastereomer) M Chemistry 322a / 325a -3- Exam No. 3 (2) (15) (A) (10) Circle the structures below that are chiral. CH3CHCH2CH2gCH3 CH3 CH3 CH3 (CH3)2CHCH2CHCH2CHCH3 NH2 (B) (3) The compound 2~amino—1-pheny1propane (I), more commonly called amphetamine, is chiral. While both enantiomers are stimulants of the central nervous system, the (R) stereoisomer is more active. Complete the stereodrawing below for (R)—2-amino—1- phenylpropane by placing the four atoms/ groups around the stereocenter in the order requested, where (A) is the highest priority and (D) is the lowest p 'rity group. INHz C6H5CH2CHCH3 I (R)-2-amino-1-phenylpropane (C) (2) If optically pure (R)—2-amino-1—phenylpropane (100% ee) has a specific rotation of [0‘];5 = - 40° what is the mixture of (R) and (S) enantiomers in a sample of amphetamine that shows [0611135=+2o° 2: —-7—§-— l A/IKdG‘HY %R %5 answer MUM-Z, “WWW " 5:2 oW/frh‘44. Chemistry 322a / 325a Name Exam No.3 2 «([94 0 WW W. (3) (20) Circle the answer that correctly complet 3 each question or statement below. (A) The general structure of the prescription drug Darvon (an analgesic) is show below. Q—CCHZCH3 CGHSCHZQCH(CH3)CH2N(CH3)2 C6H5 Darvon (circle correct answer) -There is one stereocenter in Darvon and the number; of stereoisomers is 2. -There are two stereocenters in Darvon and the number of stereoisomers is 2. -There are two stereocenters in Darvon . d the number of stereoisomers is 3. -There are two stereocenters in Darvon and the number of stereoisomers is 4. (B) Which statement is correct about the structures below? -II is the meso diastereomer. -II and III are the enantiomers of the meso diastereomer. —Ou ' the meso diastereomer. -I and III are the same stereoisomer which is the meso diastereomer. (C) The compound 2,3,4-trichloropentanoic acid had three stereocenters as shown in the structure below. The configurations at the stereocenters for four stereoisomers of this compound (there are more) are shown (I, II, III and IV). The two stereoisomer that are enantiomers are $0014 cOOH cOOH cOOH cOOH t 1‘ 2:2: 11 t t t *ch1 F F F F CH3 CH3 CH3 CH3 CH3 II III IV 2,3,4—trichloropentanoic acid I (circle answer) I and II II and III « III and IV II and IV Chemistry 322a / 325a -5- Name Exam No. 3 (3) Contd. (D) Three Fischer projection formulas of 2—butanol are shown below. (circle correct answer) -The stereocenter in I is (S) and the other formula that is (S) is 11. -The stereocenter in I is (S) and the other formula that is (S) is III. ~The stereo -r in I is R and the other formula that is R is 11. -The stereocenter in I is (R) and the 0 er ormu at at is (R) is 111. (E) The structure below that represents the most stable conformation of cis-l-isopropyl-4-methy1cyclohexane is (circle answer below) H3 CH3 H (CH3)CH H (CH3)CH CH H 3 (madam H (CH3)CH (F) The energy barrier of almost 11 kcal/mol during interconversion of the chair conformations of cyclohexane is associated with the highly strained conformation (circle answer below) owwd planar pure boat twist boat half chair (G) In the reaction of methyl iodide with sodium methoxide in methanol, when the concentration of methyl iodide is doubled and the concentration of sodium methoxide is doubled, the reaction rate will circle answer belo increase by factor of 4. not change. CH3I + NaOCH3 —————+ methanol increase by factor of 2. slow down by factor of 2. Chemistry 322a / 325a -6- Name Exam N o. 3 (3) Contd. (H) Which statement correctly describes the reactivities of the following alkyl bromides in an 8N1 reaction? Pr CH3CHCH2CH3 (CH3) 3C'BI' CH3CH2CH2CH2BI' II III (circle correct answer) -They will all react at the same rate. -The reactivity order will be I>II>III. initial [R—X] Initial [Nu'] Initial Rate (mole L'1 3'1) 0.050 M 0050 M 1.0 x 10-: 0.100 0.050 2.0 x 10' 0.100 0.100 2.0 x 10:;1L 0.200 0.200 4.0 x 10 E (circle correct answer) -The s mbol for this reaction is 8N1 and the rate = k[RX] [Nu']. -The s mbol for this reaction is N1 and the rate = k 3 . - The symbol for this reaction is 8N2 and the rate = k[RX] [Nu']. -The symbol for this reaction is 8N2 and the rate = k[RX]. (I) The stability order of the carbocations below is ¢H3 + + + . CHscECHLCHZ CH3CFHCH2CHCH3 CH3QCH2CH2CH3 CH3 CH3 CH3 I II III (circle answer) I>II>III III>II>I II>I>III III>I>II Chemistry 322a/ 325a - -7- Name Exam No. 3 (4) (10) When (R)-(+)-glyceraldehyde (I) (the dextrorotary enantiomer only) is reacted first with sodium cyanide in water, and then aqueous acid and heat in a hydrolysis reaction, two products are formed (A and B). Both have the general structure of 2,3,4- trihydroxybutanoic acid (shown below). These two products are separable by ordinary physical methods and each is optically active. CIIOOH CH = -- HOH (i) NaCN/HZO (u) H30+, H20, heat "E I 17C. ————-—-—-> —--—-———-—> . é‘ OH hydrolysis é‘ 0H CHZOH CHiOH (I) (R)—(+)-glyceraldehyde 2,3,4-trihydroxybutanoic acids Two products are formed that are separable by ordinary physical methods.Each is optically active. When the separated 2,3,4-trihydroxybutanoic acids are each reacted with nitric acid, an oxidation reaction occurs yielding tartaric acid products. A yields an optically inactive tartaric acid while B yields a levorotatory tartaric acid as shown below. SEOOH QOOH HNO3 *QHOH >‘QIHOH —> = HO,h t E: H'E‘OH 2 ea H';‘0H .d t. _ CHZOH ox} a 10“ COOH tartaric acids optically inactive tartaric acid A ----------- > C optically inactive (-)-tartaric acid tartaric acid D (-)-tartaric acid (A) (4) Complete the structures for the tartaric acids in the boxes labeled C and D above. (B) (4) Based on the structures for C and D, complete the structures in the boxes labeled A and B above. (C) (2) What is the term that describes the stereochemical relationship between A and B)and C and D? D \ «Charge «V—Vfi /—_—————— Chemistry 322a/ 325a -8— Name Exam No. 3 (5) (10) Write out the best possible synthesis of 2,2-dimethyl-3-heptyne by selecting starting materials and reagents from the allowed starting materials in the box below. Your proposed synthesis should be a series of chemical equations clearly showing starting materials and products for each step. It is not necessary to show any mechanistic details. allowed materials QHS ¢H3 CH3cc3‘2‘CCH2CHZCH3 CH3CH2CH2CECH CH3 PCIECH 3 CH3 CHsCHzCHzBr NaOCHZCHg/CH3CH20H 2,2—dimethyl—3-heptyne ’ NaNH2 / liq. NH3 Chemistry 322a / 325a -9- Name Exam No. 3 (6) (15) A substitution reaction A+B—C————————-—>A-B+c is a one-step reaction. It is exergonic by 10 kcal/mol and has a AGi= 8.0 kcal/mol. (A) (10) Draw the free energy diagram for this reaction below. Note the free energy axis is relative energy referenced to the starting state. In your diagram, show the product state, draw a quantitatively correct free energy diagram connecting the reactant and product states , identify the transition state with an arrow and the label TS, identify the standard free energy change and the free energy of activation in your diagram and put in the correct energy values. kcal/mo TS 5 E6 g 8.0 ton /w\ 3 £3 0 Q) .2 E 8 B ‘l‘ C (Predwd' s—t—ail‘u) progress of reaction ———> ( e-AG/RT) (B) (5) Explain the significance of the "energy factor" in terms of the above free energy diagram. Tkk QM: 1-51 44 gJ‘or Chemistry 322a / 325a -10- Name Exam No. 3 (7) (15) Compound I reacts rapidly. in a hydrolysis reaction (acetone is a co-solvent) to produce a mixture of two alcohol products. The initial rate of this reaction is given by rate = k[I]. (A) (4) Provide detailed structures for thohol products in tlmcms Zelow. 4 1‘ M F e ‘ I) )c O K CH l 3 i1 H20 H I CH3 acetone two alcohol products (B) (2) How are the two products related? Constitutional isomers, enantiomers, or diastereomers? MAJ-PS (C) (1) Will these two products have identical or different physical properties? ,(Ljéebkaf (D) (8) Provide a mechanism for this reaction as a series of chemical equations. Your mechanism must include and identify the rate-determining step for this reaction, nd show how two alcohol products are formed. Use the curved a formalism. Th5 rs ova SAN Next—~90“. Q (’63 H"). : ffifitb ' i— a? k 2L0“: aca-t—OMK H qu—EO C CL—H D44 \ N1?“ MLdeO—‘FK ({IJX @L(\ V -> — Q C 0H). H 5K6; C‘5/ “ Wei L— i», #954“ 5 + H3069 ‘ ...
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