NH2 N C- NH OH N一NH二 H CH CH N H N一H N OH 互变异构 H CH 3 N CHN N O NH C NH NH2 H CH3 _ + OH _ - iii NH2 N N N N CH3 互变异构 H _ + OH _ - N N H CH3 NH N N HO ,, H N N H CH3 NH N N