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Chemistry Forums for Students => High School Chemistry Forum => Chemistry Olympiad and other competitions => Topic started by: Radu on March 25, 2014, 03:41:40 PM

Title: The first problem
Post by: Radu on March 25, 2014, 03:41:40 PM

      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:
                       μwater=sqrt2*μO-H*sqrt(1+cos105°). Hence, μO-H=1.5158 D .
                       Analogously:  μdiethylether=sqrt2*μO-C*sqrt(1+cos110°). Whence,
     μO-C=1.12788 D .
                 Now, for methanol: α=(μ2methanol2O-C2O-H)/2μC-OμO-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.

Title: Re: The first problem
Post by: Rutherford on March 25, 2014, 04:06:02 PM
I got the same. It's probably because of the neglected C-H interaction.