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162 Chapter 8 HYDROXY FUNCTIONAL GROUP: ALCOHOLS: PROPERTIES, PREPARATION, AND STRATEGY OF SYNTHESIS HO (b) CH₃CHCOH O Only the ketone carbonyl is reduced in these. (c) OH 59. OH OH 0 C C H CH₃ and H CH₂COH COH COH O 60. The bottom (α) face of the steroid is less hindered. CH₃ HO HO CH₃ HO CH₃ CH₃ (a) (b) CH₃ CH₃ H H H H H H HO H H 61. The hydrogen atoms in hydroxy groups are acidic enough to react virtually instantaneously with the highly basic metal-bearing carbon atom of a Grignard or a lithium reagent. This process, which is an acid- base reaction, destroys the organometallic reagent by protonating this carbon and forming an inert alkane. The alcohol group is converted to its conjugate base, an alkoxide, with a positively charged magnesium or lithium counterion. Such acid-base reactions are much faster than addition reactions of organometallic reagents to carbonyl group double bonds. Therefore, enough excess organometallic species has to be introduced to compensate for the amount that is destroyed by this acid-base process, with enough left over to then add to the carbonyl groups in the substrate molecule. 62. Design each strategy beginning with disconnection of one of the bonds to the alcohol carbon atom (the "strategic bonds"). OH O a b a b CH₃MgBr + + CH₃CH₂MgBr c MgBr O + consider how readily available (and if available, how expensive) are the starting materials arising from each disconnection. For Grignard reagents, consider the corresponding halides; for ketones, consider the corresponding alcohols: