Organic Chemistry Paula Y. Bruice Seventh Edition

Transcription

1 rganic hemistry Paula Y. Bruice Seventh Edition

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3 64. a. Draw resonance contributs f the following species. Do not include structures that are so unstable that their contributions to the resonance hybrid would be negligible. Indicate which are maj contributs and which are min contributs to the resonance hybrid b. Do any of the species have resonance contributs that all contribute equally to the resonance hybrid? 65. Which ion in each of the following pairs is me stable and why? a. b. c. d. 66. Which compound would you expect to have the greater heat of hydrogenation, 1,2-pentadiene 1,4-pentadiene? 67. Which resonance contribut in each pair makes the greater contribution to the resonance hybrid? a c. 3 3 b. d lassify the following species as aromatic, nonaromatic, antiaromatic: a. Which oxygen atom has the greater electron density?

4 b. Which compound has the greater electron density on its nitrogen atom? c. Which compound has the greater electron density on its oxygen atom? Which compound is the strongest base? Which can lose a proton me readily, a methyl group bonded to cyclohexane a methyl group bonded to benzene? l triphenylmethyl chlide 72. The triphenylmethyl cation is so stable that a salt such as triphenylmethyl chlide can be isolated and sted. Why is this carbocation so stable? 73. a. The B ring of ctisone, a steroid, is fmed by a Diels Alder reaction using the two reactants shown here. What is the product of this reaction? ctisone 3 2 b. The ring of estrone (a steroid) is fmed by a Diels Alder reaction using the two reactants shown here. What is the product of this reaction? estrone Answer the following questions and explain the reason f each answer: a. Which compound is a stronger acid? 398

5 b. Which compound is a stronger base? 75. Draw the resonance contributs f the following anion and rank them in der from most stable to least stable Rank the following compounds in der from most stable to least stable: 77. Which species in each pair is me stable? a. 2 3 c b Which species in each of the pairs in Problem 77 is the stronger base? 79. Purine is a heterocyclic compound with four nitrogen atoms. a. Which nitrogen is most apt to be protonated? b. Which nitrogen is least apt to be protonated? purine 80. Which of the following compounds is the strongest acid? d. 81. Why is the delocalization energy of pyrrole (21 kcal/mol) greater than that of furan (16 kcal/mol)? pyrrole furan 399

6 82. Rank the indicated hydrogen in the following compounds in der from most acidic to least acidic: Answer the following questions f the p molecular bitals (Ms) of 1,3,5,7-octatetraene: a. ow many Ms does the compound have? b. Which are the bonding Ms and which are the antibonding Ms? c. Which Ms are symmetric and which are antisymmetric? d. Which M is the M and which is the LUM in the ground state? e. Which M is the M and which is the LUM in the excited state? f. What is the relationship between M and LUM and symmetric and antisymmetric bitals? g. ow many nodes does the highest-energy M of 1,3,5,7-octatetraene have between the nuclei? 84. ow could you synthesize the following compound from starting materials containing no me than six carbons? (int: A 1,6-diketone can be synthesized by oxidative cleavage of a 1,2-disubstituted cyclohexene.) 85. A student obtained two products from the reaction of 1,3-cyclohexadiene with Br 2 (disregarding stereoisomers). is lab partner was surprised when he obtained only one product from the reaction of 1,3-cyclohexadiene with Br (disregarding stereoisomers). Account f these results. 86. ow could the following compounds be synthesized using a Diels Alder reaction? a. b. 2 3 c. d. 87. a. ow could each of the following compounds be prepared from a hydrocarbon in a single step? Br Br 3 b. What other ganic compound would be obtained from each synthesis? 88. Draw the products obtained from the reaction of 1 equiv Br with 1 equiv 1,3,5-hexatriene. a. Which product(s) will predominate if the reaction is under kinetic control? b. Which product(s) will predominate if the reaction is under thermodynamic control? 89. ow would the following substituents affect the rate of a Diels Alder reaction? a. an electron-donating substituent in the diene b. an electron-donating substituent in the dienophile c. an electron-withdrawing substituent in the diene 90. Draw the maj products obtained from the reaction of one equivalent of l with the following compounds. F each reaction, i ndicate the kinetic and thermodynamic products. a. 2,3-dimethyl-1,3-pentadiene b. 2,4-dimethyl-1,3-pentadiene 400

7 91. The acid dissociation constant (K a ) f loss of a proton from cyclohexanol is 1 * a. Draw an energy diagram f loss of a proton from cyclohexanol. K a = b. Draw the resonance contributs f phenol. c. Draw the resonance contributs f the phenolate ion. d. n the same plot with the energy diagram f loss of a proton from cyclohexanol, draw an energy diagram f loss of a proton from phenol. e. Which has a greater K a, cyclohexanol phenol? f. Which is a stronger acid, cyclohexanol phenol? 92. Protonated cyclohexylamine has a K a = 1 * Using the same sequence of steps as in Problem 91, determine which is a stronger base, cyclohexylamine aniline Draw the product products that would be obtained from each of the following reactions: 3 a Δ c Δ b Δ 94. What two sets of a conjugated diene and a dienophile could be used to prepare the following compound? 95. a. Which dienophile in each pair is me reactive in a Diels Alder reaction? b. Which diene is me reactive in a Diels Alder reaction?