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Solutions to Problems . 395 nitro- H O. 53. (a) N N H n (b) N=C C=N H₂. PtO₂ H₂N NH₂ 0 N=C C=N HO OH CH: 0 (c) N=C N=C + C=N: + H C=NH + NH NH N=C + H N=C H H + ( NH₂ NH₂ N=C H N=C Then continue as in Problem 51 and repeat at the other nitrile group. 54. In A and B, the most acidic hydrogens are α-hydrogens. Deprotonation followed by protonation provides a mechanism for isomerization. H H LDA THF H H H A (Similar for B) In C the most acidic hydrogens are on nitrogen. The α-hydrogens are not so no isomerization is observed. 55. The mechanisms are related to amide formation and Hofmann rearrangement. respectively. In the formation of phthalimide, only those proton transfers that occur along the pathway to the product are shown. + :NH, 0 + OH