the boy bought a new dictionary to which he turned for help.这句话中的"to which"怎么理解

turn to for help : 向某人寻求帮助
这里就是他买了一个新字典来向这个字典请求帮助
turn to for help
to which 就是to dictionary

先行词是dictionary
所以定语从句完整起来就是 he turned to dictionary for help

to which 不应该单独来理解，因为to其实是和turned共同构成短语turn to，表示“向。。。”，如果用陈述语句来理解的话可以表示成he turned to a new dictionary for help。

which代指dictionary,意即he turned to dictionary for help