We're having some doubts about the accuracy of the energyE() (π nucleophilicity) calculations that we use to predict the results of electrophilic aromatic substitution reactions. Sepcifically, we think that the values for toluene are inaccurate. Can you tell us the source of the HMO parameters that you use for these calculations, especially the ones you use for the CH3 group?
It would be nice to compare the HMO parameters f.e. between the
pi-donor substituents -NR2 -OR -Cl -Br -J and the hyperconjugated
-CH3 group. All these should give a lower energyE(+) for para
and ortho positions. But -CH3 gives for para an E(+) 2.5354
being nearly the same as for the unsubstituted benzene 2.5359.
The values should show more difference.
Is there a documentation of these HMO-parameters? We only found the
hint look in Streitwieser's book.
Hans-Ulrich and Julia