http://icho2014.hus.edu.vn/Preparatory-Problems/0001/01/Preparatory-Problems-224.html I am having a problem with the first problem, the last question. I obtain a value of 101.75° for C-O-H angle in methanol, when it should be clearly between 105°(water) and 110°(diethylether), it actually is 108°.

Here's my work:

Applying a consequence of cosinus theorem:

μ

_{water}=sqrt2*μ

_{O-H}*sqrt(1+cos105°). Hence, μ

_{O-H}=1.5158 D .

Analogously: μ

_{diethylether}=sqrt2*μ

_{O-C}*sqrt(1+cos110°). Whence,

μ

_{O-C}=1.12788 D .

Now, for methanol: α=(μ

^{2}_{methanol}-μ

^{2}_{O-C}-μ

^{2}_{O-H})/2μ

_{C-O}μ

_{O-H}.

Is there any mistake? Maybe they neglected C-H interactions, even if they are more or less included in experimental C-O dipole moment from diethylether.