Columbia University 92CORG14.DOC CHEM S3443D Summer 1992 Professor Grace B. Borowitz Exam No. 4 July 2, 1992

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1 olumbia University 92RG14.D EM S3443D Summer 1992 Professor Grace B. Borowitz Exam No. 4 July 2, 1992 Name: Grade: Please use a non-red pen. Answer questions in the provided space. If you write any answers on the back of the page, indicate this on the front of that page. Points appear in parentheses ( ). Good Luck! Question Max. Pts. Points = (2 2) (2 2) (1 1 2 = (2 2) = (1 2 1) (11112) 2 = ( ) = (3 3) = (2 2 2) = 12 Total = (06) Distinguish the following compounds by giving 1 simple chemical test for each pair. Write the equations for the positive results and note the visible changes. You may use differences in chemical behavior. a and b. Ph and Ph Ph rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz 1

2 2. (20) omplete the following reaction sequences. Be specific if a particular stereoisomer is formed and note its stereochemistry. a Et 2 - B 3 2., - A - Br B b. 3 3 conc. 2 S 4 major D minor c. N: _ I R 4 N 2 / 2 l 2 E (S) Iodooctane d. ( 3 ) 3 ( 3 ) 3 u Li (3 ) 2 - Br F Br 2 G e Br Br 2 - N 2 N 3 (l) g 2, 2 2 S 4 I f. Br 2 2 J K - 2 L rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz 2

3 3. (14) a. Determine the (E), (Z) or (R), (S) nature of the compounds below. Show how you arrived at your choices. (1) (2) 3 3 _ 3 b. From the list of the following reagents, choose all those that can be reliably used in the best method to prepare t-butylmethyl ether. (1) sodium methoxide and 2-bromo-2-methylpropane (2) methanol and 2-bromo-2-methylpropane (3) potassium t-butoxide and methyl iodide (4) 1. 2-methyl-1-propene, g(ac) 2,, methanol; 2. sodium borohydride (5) sodium methoxide and 1-bromo- 2-methylpropane c. Which two of the above methods would be superior in synthesizing t-butylmethyl ether? d. What is the relationship between alcohols I and II? 3 I II (1) Different conformations of the same compound. (2) onstitutional isomers (3) Enantiomers (4) Diastereomers (5) Identical 3 e. omplete the following reaction. 2 - I M 2 f. Which reagent(s) would you use to convert 3 ( 2 ) 6 2 to 3 ( 2 ) 6 2? (1) Na B 4 / 2 (2) LiAl4/Et 2, then 3 (3) 2 /Pt (4) P/ 2 l 2 (5) Zn, (6) Sn, l rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz 3

4 4. (20) a. Fill in the intermediates and product in the following reaction sequence. 3 -I Mg ( 3 ) Et 2 N , 2, r P b. Which reagents listed below, if any, would you use to carry out the following conversion?? (1) 1. Sl 2, 2. Mg. Et 2, 3. 3 =, then 3 (2) 1. Sl 2, 2. Li, Et 2, 3. ( 3 2 ) 2 uli, 4. KMn 4, - (3) 1. -Br, 2. Li, Et 2, Li, then 3 (4) 1. -Br, 2. Mg. Et 2, 3. (5) None of the above., then 3, 4. P, 2 l 2 c. Arrange the following organometallic compounds in order of decreasing reactivity (most reactive to least reactive) with carbonyl compounds. (1) R 2 d (2) RLi (3) RMgBr (4) R 2 g (5) RK d. Fundamentally, tert-pentyl alcohol does not undergo oxidation by 2 r 4 because: (1) the intermediate chromate ester is not formed (2) the alcohol undergoes dehydration (3) the intermediate chromate ester cannot lose hydrogen. (4) the oxidant isn t is a sufficiently high oxidation state. (5) Actually, this oxidation does occur. e. (1) The allyl radical has (#) electrons in bonding molecular orbitals. (2) Butadiene has (#) electrons in bonding molecular orbitals. (3) Benzene has (#) electrons in degenerate bonding molecular orbitals. (4) The lowest energy molecular orbital of benzene has (#) electrons in its lowest energy molecular orbital which looks like the following: (Fill in the picture). f. Give 4 necessary and sufficient characteristics for defining aromaticity. rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz 4

5 5. (16) a. 2 =-=( 3 ) 2 reacts with Br 2 in l 4 at a higher temperature, rather than a lower temperature, to give mainly: (1) Fill in the structure of the product. (2) Show the structure of the important intermediate formed. (3) Is this the kinetic or the thermodynamic product? (4) Briefly, explain why a kinetic or thermodynamic product is possible for bromination of 1,3- butadienes. b. Which carbocation would be most stable? (1) (2) (3) (4) (5) c. Which diene and which dienophile would you choose to synthesize the following compound? Fill in the structures of the diene and dienophile and show the direction of electron flow leading to the product. 3 3 Diene Dienophile > d. Rank the following dienes in order of decreasing reactivity (most reactive to least reactive) toward a Diels-Alder reaction with maleic anhydride? (1) (2) (3) (4) (5) rder: rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz 5 3

6 6. (12) a. Synthesize the target molecule, acetophenone, in 2 different ways from bromobenzene. Each of the syntheses must use an organometallic reactant or intermediate in some way. More than one step may be necessary for each synthesis. Br 3 b. Which set of conditions does not result in allylic halogenation of an alkene? (1) l 2 at 400 o (2) l 2 in l 4 at 20 o (3) l 2, R-R, hm (4) Br 2 at low concentration in l 4 (5) N-bromosuccinimide in l 4, R-R, trace Br, D c. Which of the following is not true of benzene? (1) Benzene tends to undergo substitution rather than addition. (2) The carbon-carbon bonds of benzene are alternately short and long around the ring. (3) All of the hydrogen atoms of benzene are equivalent. (4) nly one o-dichlorobenzene has ever been found. (4) Benzene is more stable that the hypothetical compound 1,3,5-cyclohexatriene. d. Which of the following would you expect to be aromatic? You may choose more than one answer. : (1) (2) (3) (4) : N (5) (6) rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz 6

7 7. (12) a. Fill in the proper reagent for carrying out the following reactions. ( 3 ) Q ( 3 ) 3 2 ( 3 ) R ( 3 ) ( 3 ) 3 l S ( 3 ) 3 b. Which reagent(s) would serve as the basis of a simple chemical test that would distinguish between benzene and 1-hexene? (1) Ag(N 3 ) 2 (2) Br 2 in l 4 (3) AgN 3 in Et (4) Znl 2 in l (5) cold dil. KMn 4 c. We now know that the two Kekule structures for benzene are related in the following way: (1) They are equally correct as a structure for benzene. (2) Benzene is sometimes one structure and sometimes the other. (3) The two structures are in a state of rapid equilibrium. (4) Neither of the two structures adequately describes benzene; benzene is a resonance hybrid of the two. (5) None of the above. d. Which annulene would you not expect to be aromatic? (1) [6]-annulene (2) [14]-annulene (3) [16]-annulene (4) [18]-annulene (5) [22]-annulene rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz 7

8 rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz8 Scrap Paper rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz 8

9 Scrap Paper Good Luck in rgo II and in your careers. Grace B. Borowitz7/02/92 rganic hemi 3443D, olumbia U, Su92, Exam 4 - Final Exam, 07/02/92; Dr. G. B. Borowitz 9