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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 $\ce{CF3+}$?

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  • $\begingroup$ 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" $\endgroup$ – Yusuf Hasan Sep 22 '20 at 5:28
  • $\begingroup$ Do not use HW tag, it specifically says so. Also, MathJax in the title reduces searchability. Use $\ce{}$ for chemical compounds. $\endgroup$ – Safdar Faisal Sep 22 '20 at 5:42
  • $\begingroup$ 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. $\endgroup$ – Aniruddha Deb Sep 22 '20 at 5:45