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11.45 a) The DU for this compound is 2. b) The disappearance of the bromine color is an indication of the presence of a carbon-carbon pi bond(s) in the compound. c) Catalytic hydrogenation of the unknown yields a product with two more hydrogens in its molecular formula than that of the unknown. This indicates that there is only one carbon-carbon double bond in the unknown. The second DU must be due to a ring. d) 11.46 a) The DU of the compound is 2. b) The product of the catalytic hydrogenation has DU = 0, so the unknown compound must have two pi bonds. c) The result of hydrogenation in the presence of Lindlar catalyst shows that the unknown has a carbon-carbon triple bond. d) CH₃ 11.47 Addition reactions involving boranes are regioselective and are greatly influenced by sterics. Since the carbons of the double bond are both monosubstituted, BH₃ adds to both carbons, but gives slightly more of the product in which it has added to the less hindered carbon attached to the methyl group. This steric effect is more pronounced with disiamylborane because it has two bulky alkyl groups attached to the boron. Therefore, disiamylborane adds almost entirely to the less hindered carbon. 11.48 In this reaction, the primary carbocation intermediate is more stable than the secondary carbocation because the strong inductive electron withdrawing effect of the CF₃ group destabilizes the secondary carbocation more. Therefore, the reaction occurs with anti-Markovnikov regiochemistry. 188