In vain在句子中干什么成分？能不能放到句子的后面即to place的后面？

In vain they rush frantically round from place to place,trying to escape from acenging boredom by mere clatter and motion.

不能。这里，in vain 是修饰全句的，包含目前分词的内容。假如放在分词的逗号之前，说明只能修饰前文，不修饰分词，句意会差别非常大。不同对照如下：

In vain they rush frantically round from place to place, trying to escape from acenging boredom by mere clatter and motion.

他们疯狂地从一个地方跑到另一个地方，企图以闲聊和乱窜来摆脱无聊，这是徒劳的。
They rush frantically round from place to place in vain, trying to escape from acenging boredom by mere clatter and motion.

他们徒劳地疯狂地从一个地方跑到另一个地方，企图以闲聊和乱窜来摆脱无聊。