Answer to Question #84646 in Inorganic Chemistry for Sk Abidur Rahaman

Question

Between CH3 and CF3 one is pyramidal and the other one is planer.Which one is which and why? explain

Answer 1

There are two important effects that contribute to the pyramidalization of CF3 radical:

1) Electron-electron repulsion;

2) Hyperconjugation.

The unpaired electron on carbon repulses more with the lone pairs on the fluorine atoms in the planar geometry (predicted by sp2 hybridization) than in the pyramidal geometry (sp3).

There is also a hyperconjugation-type stabilization in the pyramidal geometry, between the orbital that contains the lone pair and the C-F antibonding orbital.

In the planar geometry the orbitals are perpendicular and no overlap occurs.