# Comparing stability of CF3+ and CD3+ [duplicate]

This is a question from my text book.

Compare the stability of carbocation between $$\ce{CF3^+}$$ and $$\ce{CD3+}$$.

The answer is given $$\ce{CF3+}$$ due to backbonding.

But I see backbonding as a sort of resonance effect. And we know that for fluorine atom its inductive effect dominants its resonance effect, and so overall it is electron withdrawing. So, shouldn't the answer be $$\ce{CF3+}$$?

• Do you know Bent's rule? That should simplify comparisons here: in the CF3 cation, most of the p-character will shift towards the fluorines, and hence the central carbon bearing the positive charge will be left with a lot of s character as compared to the carbon of the CD3 cation. For the same quantum number, s orbitals are usually lower in energy than p orbitals(and that is anyway true for 2s and 2p) so the CF3 cation will probably be experiencing a greater lowering of energy, and hence be more "stable" – Yusuf Hasan Sep 22 '20 at 5:28
• Do not use HW tag, it specifically says so. Also, MathJax in the title reduces searchability. Use $\ce{}$ for chemical compounds. – Safdar Faisal Sep 22 '20 at 5:42
• for fluorine atom its inductive effect dominants its resonance effect - no it doesn't. Do you know how bonding in $\ce{BF3}$ works? Same thing here. – Aniruddha Deb Sep 22 '20 at 5:45