# What is the configuration of dimethyl[tris(trifluoromethyl)]-λ⁵-phosphane?

I know that $$\ce{(CH3)2P(CF3)3}$$ is geometry of trigonal bipyramid and according to Bent's rule $$\ce{CH3}$$ goes to axial positions and $$\ce{CF3}$$s remains on equatorial positions. However, as per Bent's rule more electronegative ligand goes to axial position.

Now my question is how to determine which is more electronegative between $$\ce{CH3}$$ and $$\ce{CF3}$$?

You can note that $$\ce{-CH3}$$ shows electron releasing (+I) effect while $$\ce{-CF3}$$ shows strong electron withdrawing effect. Now, you can treat inductive effect as the organic analogue of electronegativity, giving axial positions to $$\ce{-CF3}$$ and equatorial ones to $$-\ce{CH3}$$ in accordance with Bent's rule.