What is the approximate H-C-H bond angle in Methylamine? Please somebody help.?

Answer 1

Because of steric effect, due to presence of amine group (H2N-), the three tetrahedrical angles in H-C-H that one could expect was 109° are reduced to a lesser degree. Frankly I do not how much but I could find a site that maybe explains better this situation:

http://www.usm.maine.edu/~newton/Chy251_253/Lectures/Shapes/Shapes.html

Good luck!

Answer 2

The point about the general hybridization being sp3 is correct as well as the other posters point that there won't be preservation of the 109.5 bond angle because the amine group isn't equivalent to the H's is also true. The point about the JT effect is not correct because the classical JT effect of reduction of symmetry from C_3v to C_s or lower requires the molecule to have C_3v symmetry to begin with, which this molecule does not. However there may be psuedo-JT effects that will effect the bond angles.

The problem with this kind of question is that fundamentally the problem requires computation or experimental measurement. You can probably find these values by going to web of knowledge and doing a search on CH3NH2.

But most importantly the H-C-H bond angles are not equivalent so you cannot actually give an answer!

Answer 3

Since the methyl group is sp3 hybridized, the H-C-H will be close to the 109.5 degrees of tetrahedral geometry. There will be a bit of Jahn-Teller distortion but likely not enough to measure.