Solutions_Manual_for_Organic_Chemistry_6th_Ed 149

Solutions_Manual_for_Organic_Chemistry_6th_Ed 149 - 7 - 1 7...

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Unformatted text preview: 7 - 1 7 E2 elimination requires that the H and the leaving group be anti-coplanar; in a chair cyclohexane, this requires that the two groups be trans diaxial. However, when the bromine atom is in an axial position, there are no hydrogens in axial positions on adj acent c arbons, so no elimination c an occur. c� C H3 h ydrogens lrans diaxial lo lhe Br H 7- 1 8 B r -- axial (X)'" � H ( a) ' Br => � � T -1 H Br axial � KOH H + 7-19 (a) ( b) S howing the chair form of the decalins makes the answer clear. The top i somer locks the H a nd the O r i nto a trans-diaxial conformation--optimum for E 2 elimination. The bottom i somer h a s B r equatori al where it is exceedingly slow to eli minate . (D H Br H Br C:::::> = Br � T � atOrial H H c{(; • C H3 the only H trans diaxial M ode ls are a b i g help for this problem. NaOCH3 .. the only elimination product H H (b) D (from elimination of H and B r) b oth trans diax ial­ gives two products + H H H (from elimination of D and B r) 1 42 = h W : H H H ...
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