20.39(a)The rearrangement in this problem is an acyl transfer from nitrogen to oxygen.This rearrangement takes place in the indicated direction because it is carried out in acidsolution. The amino group is protonated in acid and is no longer nucleophilic.(b)The trans stereoisomer of compound A does not undergo rearrangement because when theoxygen and nitrogen atoms on thefve-membered ring are trans, the necessary tetrahedralintermediate cannot form.20.40The ester functions of a polymer such as poly(vinyl acetate) are just like ester functions of simplemolecules; they can be cleaved by hydrolysis under either acidic or basic conditions. To preparepoly(vinyl alcohol), therefore, polymerize vinyl acetate to poly(vinyl acetate), and then cleave theester groups by hydrolysis.20.41(a)Each propagation step involves addition of the free-radical species to the b-carbon of a mole-
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