Can we find a 'natural' bond length and force constant for bond stretching
which would be somewhere between those for C-C and C=C? Will they reproduce
Yes: Allows simple benzene derivatives to be dealt with using these
parameters by methods previously discussed.
New parameters to add: Car - Cca ; kar
Good results for benzenoid hydrocarbons using these parameters
assigned to benzene ring.
Napthalene Allinger, Sprague 172-3
- Using simple benzenoid parameters -> all bonds=
- Using 'single' and 'double' bonds ->alternating bonds =>exptal
- Why? In napthalene, the bond lengths are determined largely by
Benzene bond orders are all=and included as such in the parameters
- => Can not apply FF calculation as discussed previously except on a
case by case basis
- What about more generally?
Bond Order: Measure of E density between pi centers
- Would need potentials depending on pi-electron distribution to calibrate
- In particular, expect bond potential (force) to vary as the pi electron
density between atoms changes.
- Requires some sort of quantum mechanical techniques
- Full quantum mechanical techniques defeat the purpose.
- Instead - pi-quantum mechanical treatment only
Partition sigma and pi frame
- Essentially orthogonal & therefore independent
- Good assumption for planar systems