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Solutions to Problems 245 39. + H₂O BH₃, THF; then NaOH, H₂O₂ (Markovnikov hydration) (anti-Markovnikov hydration) (a) 2-Hexanol 1-Hexanol (b) 2-Methyl-2-pentanol 2-Methyl-1-pentanol (c) 2-Methyl-2-pentanol 2-Methyl-3-pentanol (d) 3-Hexanol 3-Hexanol (e) Cyclohexanol Cyclohexanol Oxymercuration-demercuration gives the same products as aqueous sulfuric acid. The carbocations formed from these substrates and are not particularly prone to rearrangement. All chiral products are formed as racemic mixtures. 40. (a) Hot. concentrated H₂SO₄ (b) Cold. aqueous H₂SO₄ (c) NaOCH₂CH₃ in CH₃CH₂OH (d) HCI in Additions [reactions (b) and (d)] are normally favored by thermodynamics (Section 12-1). For elimination to occur, conditions have to be established to drive the equilibria the opposite way. In (a) the water lost in the reversible process is protonated by the concentrated H₂SO₄, removing it from the equilibrium. No good nucleophiles are present: therefore. the carbocation undergoes loss of a proton to form the alkene. In (c) the strongly basic ethoxide ion induces bimolecular elimination and neutralizes the liberated forming ethanol and NaCl. No species electrophilic enough to add to the alkene are present in the reaction mixture. 41. The transformation proceeds through anti addition. The possible products arising from addition to the trans and the cis isomers of the starting compound are shown below. Addition to the trans isomer gives the required isomer, but as a racemic mixture with its 2R,3R because initial attack by bromine on the double bond has an equal chance of occurring from the top and bottom faces of the double bond. H CO₂CH₃ (CH₃)₂CH Br HO H Br₂, H₂O 5 R + CO₂CH₃ CO₂CH₃ R (CH₃)₂CH H HO H (CH₃)₂CH Br trans 2S.3S 2R.3R (CH₃)₂CH H Br H (CH₃)₂CH + R H H HO H H Br cis 2S,3R 2R.3S 42. All chiral products are formed as racemic mixtures. CH₂CH₃ CH₂CH₃ (a) (b) H Cl H Racemic + CH₂CH₂CH₃ H CI H mixture CH₂CH₂CH₃ CH₂CH₂CH₃