1.不是很清楚 一般3.3以内吧 个人意见
2. 应该可以  呵呵

搜一下前段时间xi2004老师发的关于C-H...O氢键的讨论的帖子
讲得很明白

我看那个帖子了，可还不是很明白，能指教一下吗？

Unlike strong hydrogen bonds, the weaker varieties are easily distorted by the crystal environment. Therefore, it is useful to discuss hydrogen-bond lengths and angles jointly. A longer C-H...O contact (D > 3.6 &Aring  may be acceptable as a hydrogen bond if the angle tends towards linearity ( > 150°). Very short C-H...O contacts (D < 3.2 &Aring  with very bent angles (90-110°) should be viewed with some scepticism. In cases of doubt, angular considerations should take precedence over length considerations.
仔细读这段话，也可以看一下这篇文献，在ISI搜一下关于这种氢键的文献，

3.2到4.0之间。

跟帖学习

这么说C-H...O的氢键键长比一般的O-H...O的氢键距离要长。
我以前只讨论d<3.0的。

一般在3.8以内，还要看键角，-CH2的C没问题