Degree of Bond Character/Valence Shell Electron Repulsion

[budullewraagh]

this morning i was looking through an organic book i am borrowing. reading about bond angles, i came across the fact that not all SP^3 bond angles are 109.5 degrees. i knew this before, but i didn't know the way to calculate the angles. this book discusses the fact that Cl-C-H bonds in CH3Cl are 108 degrees and calls the C-Cl bond an SP^3.1 and H-C-H bonds are 110 degrees with a C-H bond of SP^2.9 character, but still, it doesn't explain how one can come to these conclusions.

 

does anyone know a way to calculate the bond angles made by a central atom that is not bonded symmetrically?

 

conceivably, one could calculate this using the average positions of bonded electrons and electrons in lone pairs, as well as bond lengths, but i'd rather not do that because i believe there is a much simpler way. or at least i hope so. i can't think particularly well these days, as i've had the epstein-barr virus for 3 weeks now. mononucleosis is no fun

[akcapr]

isnt mono like HIV kinda?

[budullewraagh]

well, it's transmitted through fluid exchange, so i guess in that case it's like HIV. takes a few months to get over it usually. most of the time, people don't even notice they have it. when one's immune system isn't working particularly well, they become susceptible to it.

[Skye]

I imagine you could calculate it semi-empirically using electrostatics, I haven't done much molecular modelling though. Basically like repel, opposites attract, the stronger the electro+/- an atom is the greater the effect will be.

[budullewraagh]

right, i was thinking of using electrostatics, wave functions, angular momentum and the like, but i was hoping there would be an easier way