(c) (a) (e) 7.70 Draw a plausible mechanism for each of the following transfor- mations: (b) (g) (c) (d) (a) (b) LOH (c) (d) OH CI 7.71 When the following optically active alcohol is treated with HBr, a racemic mixture of alkyl bromides is obtained. Draw a mechanism for this process, and explain the stereochemical outcome. OTS OH Br OH 7.72 Identify the reagents you would use to achieve each of the following transformations: 8. NaOH H₂O Br conc. H₂SO4 C heat conc. H₂SO heat NASH EIGH NaOEt EIOH OH 7.73 Predict which of the following substrates will undergo a solvoly- sis reaction more quickly. Explain your choice. 7.77 Predict the major product for each of the following reactions. ? ? 1-BUCK -BUCK NaOEt EICH HBr Br ? Lil DMF SH .OH Br Lil DMF Racemic mixture (b) (d) OH (f) ? 338 CHAPTER 7 Alkyl Halides: Nucleophilic Substitution and Elimination Reactions + H₂O heat H₂? Br INTEGRATED PROBLEMS 7.80 When the following ester is treated with lithium iodide in DMF, a carboxylate ion is obtained: onلا Strong base the (a) Draw a plausible mechanism for this reaction. (b) When a methyl ester is used as the substrate (instead of an ethyl ester), as shown below, the reaction occurs ten times faster. Explain the increase in rate. thomas DEN Na Me MeOH the 7.81 When (1R,2R)-2-bromocyclohexanol is treated with a strong base, an epoxide (cyclic ether) is formed. Suggest a mechanism for formation of the epoxide: ? An epoxide + CH₂I (a) This reaction is stereoselective, and the major product is trans- stilbene. Explain why the trans isomer is the predominant product. To do so, draw the Newman projections that lead to formation of each product and compare their stability. (b) When (R)-1-bromo-1,2-diphenylethane is used as the starting sub- strate, the stereochemical outcome does not change. That is, trans- stilbene is still the major product. Explain. 7.75 There are two stereoisomers of 1-tert-butyl-4-chloro-cyclohexane. One of these isomers reacts with sodium ethoxide in an E2 reaction that is 500 times faster than the reaction of the other isomer. Identify the isomer that reacts faster, and explain the difference in rate for these two isomers. (a) 7.76 Substitution vs. Elimination: Identify the major and minor product(s) for each of the following reactions: ? (c) (f) trans-Stilbene (major product) 요 (g) Br Br +BUOK NaOEt OTS ? NaOEt EtOH NaOEt EICH 1-BUCK NaCl DMSO NaCN OMSO (b) ľ OH Heat & −? t = NaOH (d) ? ? ? cis-Stilbene 7.78 Consider the following substitution reaction: (h) NaCN DMSO CI (d) Draw an energy diagram for this process. (e) Draw the transition state for this process. NaOH NaOEt (a) Determine whether this reaction proceeds via an SN2 or SN1 process, and draw a complete mechanism. Na Me NHẤT (b) What is the expected rate equation for this process? (c) Would the process occur at a faster rate if the concentration of cyanide was doubled? (d) Draw an energy diagram for this process. ? conc. H₂SO4 ? ? CN 7.79 When 2-bromo-2-methylhexane is treated with sodium ethoxide in ethanol, the major product is 2-methyl-2-hexene. (a) Draw a mechanism for this process. (b) What is the expected rate equation for this process? (c) What would happen to the rate if the concentration of base was doubled? ? 7.84 Consider the reaction below. The rate of this reaction is mark- edly increased if a small amount of sodium iodide is added to the reac- tion mixture. The sodium iodide is not consumed by the reaction and is therefore considered to be a catalyst. Explain how the presence of iodide can speed up the rate of the reaction. 7.85 Propose a mechanism of formation for each of the following products: EICH Heat 88=7 02.0.0 OE! 7.86 When a new synthetic method is developed, it is applied to a series of compounds to explore its utility. 4-Fluorophenylacetonitrile