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Chemistry 112A, Midterm 2

Student signature: /Write TA's full name (section number) or Lecture Only:

1. Please make sure that the exam has 8 pages including this one.2. Please write your answ ers in the sp aces provided.3. Write clearly; illegible or ambigu ous answers will be considered incorrect.4. Only writing implements are allowed (N o Calculators).

GOOD LUCK!1. 60 points2. 20 points3. 13 points4. 30 points5. 20 points6. 20 points7. 12 pointsTotal 175 points

MINI-PERIODIC TABLEI I1 111 IV v VI VII VIIIH HeLi Be B C N 0 F NeNa Mg A1 Si P S C1 ArK Ca Ga Ge As Se Br Kr

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1. Answer the following questions. Every wrong answer cancels a correct answer (60 points).(a). Circle the com pound(s) that are chiral (6 points).

FF

derivatives that3)2

CH3(c). Circle the alkyl halide(s) below that would und ergo an SN2 eaction more rapidly than isopropylbromide 6 points).(5J A C I A B r @(d). Number the alkyl halides that up on reaction with NaOCH, would give the m ost to the least~2cversus SN2 products [I most E2] (6 points).

(e). Circle the correct statement(s) (6 points).1 The rate of an E l reaction does not depend on the base.4 he rate of an E2 reaction does not depend on the base.3. Five-membe red rings have more strain energy than four-membe red rings.6 earrangeme nts can occur in SN 2 reactions.Rearrangem ents can occur in SN 1 reactions.

(f). Circle the reage nts below that would produce a racemic chiral product upon reaction with 1-methylcyclopentene [see structure in box] (6 points).I

HzI ft 2. H 2 0 2 , N a O

(g). Circle the alkyl halide(s) below that would un dergo an SN1 eaction more rapidly than isopropylbromide (6 points).

2

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(h). Nurrlber the nucleophiles that provide the fastest to slowest SN2reaction [I fastest] (6points).

Circle the compounds that are in the lowestpCH30energy conformation (6 points).@$=)(j). Circle the alkene(s) listed below that upon reaction with C12 would give a racemic chiralproduct rather than an achiral product (6 points).

2. For each of the following reactions supply the missing starting materials, reagents, or major organicproducts in the space provided. Show the stereochemistry of the product. If the product is chiralindicate whether or not it is racemic (20 points total).0. Li (two equivalents)2. D20

7 O - a + NaBrBr 0o a kNa 0

acetone (solvent) *

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3. Upon treatment with sodium ter t-butoxide [( c H ~ )~ C O -N ~ '] ,he two stereoisomeric cyclohexylbromides undergo E2 reactions at different rates.

\a. C irc le the stereoisomer t h a t d f a s t e s t 2 reaction (2 points).b. Are the elimination products ch ira l? (2 points). Y45c. Ex pla in the rationale for your answer in p ar t A by drawing chair structures for the two stereoisomers(9 points).

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4 . For each of the following pairs of structures assign he isom eric relationship, i.e., diastereomeric,enantiomeric, or identical (includes conformational). In addition, circle all of the compounds that arechiral

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5a. Draw all of the possible isomers of dibromobutane (Four-carbon chain with tw o brominesattached). List enan,tiomers, but points will be ma rked off for writing the same structure twice (10points).5b. Assign the absolute configuration for each stereocenter (10 points).

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6. Upon heating the alkyl bromide in water as shown below, three products are produced. Provide amechanism for their formation (20 points).

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7. Provide a mechanism for the reaction shown below (12 points).Y ~ H @ 0:NHdtwo equivalents) - + NH,CI