Since the reaction of the bromide with NaSCH2CH3proceeds with inversion of confgurationat the stereogenic center, and since the fnal product has the same confguration as the startingalcohol, the conversion of the alcohol to the bromide must proceed with inversion of confgu-ration.(d)The conversion of 2-butanol to sec-butyl methanesulfonate does not involve any of the bondsto the stereogenic center, and so it must proceed with 100% retention of confguration.Assuming that the reaction of the methanesulfonate with NaSCH2CH3proceeds with 100%inversion of confguration, we conclude that the maximum rotation of sec-butyl ethyl sulfdeis the value given in the statement of part (b), that is,625°. Since the sulfde produced inpart (c) has a rotation of 123°, it is 92% optically pure. It is reasonable to assume that the lossof optical purity occurred in the conversion of the alcohol to the bromide, rather than in the re-action of the bromide with NaSCH2CH3. If the bromide is 92% optically pure and has a rota-
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