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Exam 1 -- Fall 2003 blank

Exam 1 -- Fall 2003 blank - Name Page 1 I(20 points A...

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Unformatted text preview: Name Page 1 I. (20 points) A. Provide structures of the missing reactants, reagents or products as indicated by the boxes. If there is more than one possible outcome, provide the maior product as implied by the conditions and any additional information given. If a box has more than one experimental step, you must number the order in which they are used. Be sure to show stereochemistry where known. (a) CH3 1% 0+ CH3 1. CH3— CEC-Li _, —> o"‘ H O 2. NH4C1, H20 (protonation) (b) Provide the m—ost suitable reagent to selectively accomplish the transformation below. (c) Draw structures for the most aggrogriate reactants for the below transformation. IOI + (KBr also produced) (d) PhS H O 0 CH3 CH3 B. Ester B undergoes nucleophilic substitution reactions taster than Ester A. Use drawings to show how changing the para substituent from a dimethylamino group [(CH3)2N-] to a nitro group [02N-] enhances the leaving group ability of the para-substituted phenoxide anion. Use only a few words to explain your drawings. . :0: : 9\@ -- II H/ —©—o C—CH3 A .OéN—Q—Q—C—CH3 B Both anions have resonance forms involving delocalizationof the negative charge into the benzene ring Name Page 2 II. (20 points) The readily reversible reaction of isobutyraldehyde with a secondary amine (Compound C) to give an enamine (Compound D) is mechanistically identical to that we discussed for imine formation up until the final site of deprotonation. : O: H " trace of acid -- ~- (CH3)2CH— C—H + Ph— NHCH3 : (CH3)2C= CH—N— Ph + H20: heat CH3 isobutyraldehyde compound C Compound D (an enamine) A. Based on the information given, provide the detailed, step-wise mechanism using the curved arrow notation for the above transformation. Do not add any other reagents. You may use H-B and B: 9 to represent a Brgzsnsted acid-conjugate base pair as needed. 18 B. Would the above reaction be successful if benzaldehyde (see structure below) is substituted for isobutyraldehyde? Briefly explain. you must circle one, however reason: points are awarded for the reason YES NO benzaldehyde Name Page 3 1]]. (20 points) I ntramolecular cyclization reactions are a part of each of the following transformations. Provide structures of the missing products as indicated by the boxes. If there is more than one possible outcome, provide the major product as implied by the reaction conditions and any additional information given. (a) Draw a Newman projection for the conformation of the bromohydrin reactant that is required for the cyclization reaction. Use the point of view where the carbon bearing the OH is in the front. Newman projection of reactant here PdellCt (show stereochemistry) HO Br \C C/ H“/' "'CHZCH3 NaOH> PhCH2 H H20 03) C18 H26 06 strong IR absorption around 1725 cm'1 0 | | I HO c— OCH3 o 0 HO —> TsOH (cat) (C) 0 (show stereochemistry) HO D II .\C _ Cfi CH3CH20- C- OCHZCH3 CH3CH2CH2CH2“ \ H —> H OH K2C03 (base) heat (d) 0 ll 0 O CH3O CH2- C- OH || || CH3-C-O—C— CH3 |CI) C- OH —,(l 6‘1“”) + 2 CH3- C— OH CH3O '6 120 0C Name Page 4 IV. (20 points) A. Draw structures for all products expected from the complete acidic hydrolysis of Compound E. CHZOCHZOCH3 0 CH3 0 0 H30?3 H20 CH3 0 CH3 Compound E B. The following preparation of Compound F was accomplished using the following sequence of reactions (J. Am. Chem. Soc. 2003, 125, 10772). (a) Complete the reaction scheme as indicated. Any important reaction conditions (catalysts, heat, stoichiometry, etc.) should be included. You do not need to specify solvents. If a box has more than one experimental step, you must number the order in which they are used. CHZOCHgPh —> . CHZOCHzPh ’CH3 draw one of two possible stereoisomers HO CHZOCHZPh CHZOCHZPh CH2=CHCH2 "I CH3 n, CH3 CH2=CHCH2 _ CH20CH2Ph o -. CP120CHzPh HO ”CH3 ’CH3 Compound F (b) Compound F would form as a mixture of stereoisomers. Answer the following questions with regard to this stereoisomeric mixture by circling the 0_ne most appropriate response for each How many optically active stereoisomers of Compound F are expected? 0 1 2 3 4 2 How many optically inactive stereoisomers of Compound F are expected? 0 1 2“ 3 4 2 Are any of these stereoisomers of Compound F related by being enantiomers? YES NO Name Page 5 V. (20 points) A. Provide structures of the missing products as indicated by the boxes. If there is more than one possible outcome, provide the maior product as implied by the conditions and any additional information given. Include stereochemistry where known. (a) 0 ~\ \ CH | v \/ 3 NaBH4 H20 , CH CeCl3 acid catalyst 3 CH CH H 0 0C O 3 20 2 pts alkene hydration 4 2 ItS correct re ioisomer (b) IR: 3600,1730 cm-1 0 CH2: CH \ C / CH20H ll s" \ C— H H NH2 \ (1 equiv.) —> N fl:— OCHZCH3 trace of acid 1:1 0 heat B. In lecture we discussed that reactions of alcohols with acid chlorides are usually performed in the presence of a mild base such as the aromatic amine, pyridine. In addition to acting as a base to prevent the development of a highly acidic solution, pyridine can also catalyze the reaction. (a) The catalytic effect is a result of a nucleophilic substitution reaction between pyridine and the acid chloride, which forms a new acylating agent that is more reactive than the acid chloride itself. Predict the structure of this highly reactive acyl transfer reagent. draw the new acyl transfer reagent 9 a — — : + \ —> R C Q] N o (pyridine) (b) Explain why the carbonyl group of the acyl transfer reagent you drew in part (a) is expected to be less stabilized than that in the acid chloride. Drawings and a few words are required for full credit. ...
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