Br vs. I

Code:

[bob@epoch authortool]$ evaluate -e "energyE()" -p 4 "Ic1ccccc1" 3.0326;2.5685;2.5061;2.5366;2.5104;2.5366;2.5061 [bob@epoch authortool]$ evaluate -e "energyE()" -p 4 "Brc1ccccc1" 3.0326;2.5685;2.5061;2.5366;2.5104;2.5366;2.5061 [bob@epoch authortool]$ evaluate -e "energyE()" -p 4 "Clc1ccccc1" 4.049;2.5849;2.4979;2.5367;2.5035;2.5367;2.4979 [bob@epoch authortool]$

It seems odd that iodobenzene and bromobenzene are giving exactly the same values. JChem 5.1.0.

No comments?

Hi,





I modified the Huckel parameters of iodo atom.  The new values are on the attached picture.  





Jozsi

Thank you.  I think it would be wise for you to check that other heavy atoms' parameters are not simply copies of their lighter congeners.





In what version will the fix be available?

Hi,

Quote:

In what version will the fix be available?

 





The fix will be available in the 5.1.5 version. This release can be excepted on February 4.





Jozsi

Hi, I have evaluated the issue of this topic and I found some results difficult to explain.





1) As can be seen in the screenshot a HMO calculation for a Astat-compound is possible. I don't know if it is more than a theoretical compound, but this calculation for it is out of the range of the HMO model.





For the command line version evaluate -e "energyE()" -p 4 "Atc1ccccc1" there is an error message.





Using only the command line tools often the problems of the GUI version are not seen.





As already suggested in an other topic the simple HMO calcualtions should be restricted to the elements for which it is designed: C O N S F Cl Br I and perhaps Se.





2) Evaluating the E-localisation energies by calculating the pi-energy for the cationic localised form it was possible to reproduce the values for the ortho, meta and para postions of fluorobenzene. The value for localized form for the ipso position can only be reproduced by assuming the pi-energy value for fluorine as 6.00 (which gives an alfa parameter 3.0).





But what's about the E-localisation energy at the fluorine itself = 6.12 ? It is obviously the difference between the pi-energy of fluorobenzene and benzene. How to explain this as a chemical reaction? Of course the very lower values for the E-localisation energies at the ring positions correspond to a higher reactivity at the ring positions, but for brombenzene the E-loc value is only 3.03 and not so far away.





Regards, Hans-Ulrich