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9.19 H Br H Et H carbocation + rearrangement + OEt OEt substitution products 9.20 A tertiary substrate with a strong base favors E2 elimination. Normally the elimination products follow Zaitsev's rule with a less hindered base like ethoxide ion, producing more of the more highly substituted + alkene. When a sterically hindered, strong base (t- BuO⁻) is used, the proportion of the less highly major substituted alkene will increase. 9.21 In the stereoisomer of ,3,4,5,6-hexachlorocyclohexane shown, the CI atoms are either all axial or all equatorial. Anti elimination cannot occur because there is no H trans to any CI. When the Cl's are axial, there are no H's in a trans-diaxial arrangement. All of the other stereoisomers of this compound will have at least one hydrogen anti to a chlorine in one of the conformations. 9.22 Ph Ph Br H Ph H H rotate Br H Ph anti Br C H Br H Br Ph Br elimination C Ph Br Ph Ph H 140