Solutions_Manual_for_Organic_Chemistry_6th_Ed 116

Solutions_Manual_for_Organic_Chemistry_6th_Ed 116 - 6-26...

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Unformatted text preview: 6-26 (d) continued alkyl migration (ring expansion) followed by nucleophilic attack H 2° + �I H CH 2 \ -.-.-----�.� : 0 -CH2CH3 CH2 / :.0-CH2CH3 . I H 6-27 (a) C H3 - �-0-C-CH3 I " CH3 0 (b) C H3-CHCH20CH3 I ( e) C H CH 2CH3 S N 1 , 3° SN2 , 1 ° C H3 o CH2CHl S N 1 , 3° S N 1 , weak nucleophile 6-28 / C H3 C I C H3 CH 3 CH2 "'H Br (R)-2-bromobutane racemization S N l­ � \.. H 2 0,� CH 3 CH 2 inversion S N2- C"" / ,'OH H I S N2, strong nucleophile H 2 0,� (S)-2-butanol CH3 + CH 3 CH2 /C"", I , OH H (R)-2-butanol (S)-2-butano 50 : 50 mixture-racemic y � If SN 1 , which gives racemization, occurs exactly twice as fast as S N2, which gives inversion, then the racemic mixture ( 50 : 50 R + S) is 66.7% of the mixture and the rest, 3 3 . 3%, is the S enantiomer from SN2. Therefore, the excess o f one enantiomer over the racemic mixture must be 3 3 . 3%, the enantiomeric excess. (In the racemic mixture, the Rand S "cancel " each other algebraically as well as in optical rotation.) The optical rotation o f pure (S)-2-butanol is + l 3.5° . The optical rotation o f this mixture is: 3 3 . 3% x + l 3.5° = + 4 .5° 109 ...
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