Valence Angle, constancy

Fig. 9. The application of the principle of the constancy of valence angle in the hydrogenation of different bonds (a) ethylene, (b) acetylene, (c) carbonyl bonds.

A second general rule that can be deduced from the existing material is the constancy of the valence angle. 

Short-range interactions, i.e. those interactions between atoms or groups separated by only a small number of valence bonds, result in an effective constancy of bond angles and in torques hindering internal rotations. 

---