Columbia University C99ORG14.DOC S3443D Summer 99 Professor Grace B. Borowitz Exam No. 4 - Final July 1, 1999

Transcription

1 olumbia University 99RG14.D S44D Summer 99 Professor Grace B. Borowitz Exam No. 4 - Final July 1, 1999 Name: Aroma T. ity and Al Lylic 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 Points Max. Points Points Earned 1. 4 = 10. ( 6 ).5.5 = 18. ( 5 5 ) 5 = = ( ) = = 1 7. = = 08 Total = (10) a. The conversion of ( ) -= to ( ) -()- is best accomplished in the laboratory with which set of reagents First B 6, then in aqueous Na () Dilute cold aqueous KMn 4 containing Na () ot aqueous Na * (4) Aqueous g(ac), then aqueous NaB 4 b. Which of the following substances does NT function as a Lewis Acid (electrophile) ( ) () BF * () :N( ) (4) Al c. Which molecule has the (S) configuration Show how you arrived at your answer for assigning the (S) configuration. N 4 c () () (4) R a b b * c S a R () S () R (4) N b R c a a b R R c 1

2 . (15) a. What is the stereochemical relationship between the following molecules A B conformers () identical * () diastereomers (4) enantiomers b. Name the molecules A and B according to IUPA nomenclature. Label the chiral carbons in the compounds above (R) or (S) according to ahn-ingold-prelog Sequence Rules and include those designations in their names. Also, designate A and B according to the appropriate descriptive terms from the following selections: meso, dl, erythro (dl), or threo (dl). 6 a S b c b R c A S, R R R B R, R A erythro (S,R)--omo--butanol B threo (R,R)--omo--butanol c. Which of the compounds below would react most rapidly with iodide ion in the S N reaction illustrated below R-l acetone I R-I l * l () l () ( ) - l (4) l.5 c. f the following, which is the best method to prepare t-butyl methyl ether ( ) - () K ) -l * () ( ) - K -I.5 (4) -I Mg ( ) - 99RG D Dr. Grace B. Borowitz

3 . (18) a. The more stable chair conformation of trans---methyl-1-tert-butylcyclohexane has: both alkyl groups in axial positions. () both alkyl groups in equatorial positions. * () an axial methyl group and an equatorial tert-butyl group. (4) an axial tert-butyl group an equatorial methyl group. b. arry out the following conversion different ways using any needed organic and inorganic reagents. /l 1. xs N N (l). N 4 g S 4, S (), or 1. g(ac),, TF. NaB 4 r 7 or KMn 4, D c. arry out the following conversion using the Grignard or organocopper reaction as one of the steps. You may use any other needed organic and inorganic reagents. Show all the intermediate steps 5 or use PhMg N followed by /, or use Ph d (=)-l, followed by hydrolys or use Ph uli (=)-l. Mg r /Fe 7 Mg, Et 1. - or., KMn 4, D 99RG D Dr. Grace B. Borowitz

4 4. (16) Fill in the missing reactants, reagents, conditions, intermediates, or products in the following reaction sequences. 4 a. b. c NaB 4 /Me. S 4, D. Ph W W (Free Radical atalyst) Polystyrene Pb n 4 (Polymer, name and write sample structure). d. Fill in all the reagents and steps necessary to carry out the following conversions. Ph Ph Ph Ph - Ph Ph Ph Ph Mg Et Ph Mg Ph Ph Ph P Ph or PD Pyridinium hlorochromate or Pyridinium Dichromate 6 99RG D Dr. Grace B. Borowitz 4

5 5. (10) a. Fill in the missing predominant organic products in the following reactions. iefly explain why each product predominates at the given temperature in terms of type of control. -15 o predominant product / l 1 mole 40 o predominant product Explanation: At lower temperature, kinetic control holds. 1,-Addition is reversible and reaction with lower E a predominates. At higher temperature, 1,-addition is reversible, 1,4-addition is not reversible, and thermodynamic control predominates. Therefore, when higher E a path is followed, more stable product builds up. b. iefly show the mechanism that gives rise to each product. 1, 1 mole - / l 1,4-15 o predominantly 1,-addition kinetic control 40 o predominantly 1,4-addition thermodynamic control c. Fill in the missing organic products in the following reaction. I I 99RG D Dr. Grace B. Borowitz 5

6 6. a. Label each set of molecules as one of the following: conformers, enantiomers, diastereomers, tautomers, resonance forms, or constitutional isomers. and * Resonance Forms () and * Diasteromers () and * Enantiomers (4) and * Tautomers l l (5) and l l * onformers (6) and * onstitutional Isomers 99RG D Dr. Grace B. Borowitz 6

7 7. (08) a. Show the distribution and relative energy levels in the molecular orbital model of benzene. Fill the orbitals with electrons as occurs in the ground state. p 6 p 4 p 5 p p p 1 b. Show the pictures of the lowest energy and the highest energy molecular orbitals of benzene. p 1 p 6 lowest energy mo highest energy mo c. iefly, define Resonance Energy or Delocalization Energy. ow is it shown in the energy profile for hydrogenation of benzene and the hypothetical cyclohexatriene E cht Ph RE D Ph D cht Definition: Resonance Energy or Delocalization Energy Reaction oordinate Energy by which the real aromatic molecule is stabilized over that of the hypothetical molecule (without interacting conjugated double and single bonds). d. Mention 4 characteristics that together define an aromatic system. (4n) p electrons planar yclic or ring onjugated 99RG D Dr. Grace B. Borowitz 7

8 8. (8) a. Which of the following would you expect to be aromatic More than one answer may be possible. () () (4) (5) (6) (7) : N (7) (8) * * * * b. Explain why is the following reaction so favorable Fill in the missing intermediate () and mechanistic arrows. ( S 4 ) = tropyllium cation is aromatic and thus specially stabilized. c. Name the type of substitution and give the detailed mechanism and products for the following reaction. l All l All All 4 d. ite a problem that occurs with this particular reaction. Show the equation. Problems: Polysubstitution l All Problem: Migration l All D, hours 99RG D Dr. Grace B. Borowitz 8

9 Scrap Paper 99RG D Dr. Grace B. Borowitz 9

10 Scrap Paper 99RG D Dr. Grace B. Borowitz 10