Hello all,
I have a question regarding the resonance of pyracyclene.
![<br />C1CC2CCC3CCC4CCC1C4C23<br />](https://www.chemicalforums.com/SMILES/24d27dc2ae2bb931cc18.png)
If I’m correct, pyracyclene has four resonance forms:
![<br />C1C=C2C=CC3=CC=C4C=CC=1C4=C23<br />](https://www.chemicalforums.com/SMILES/d5a8e14872ab21d6eab3.png)
![<br />C1C=C2C=CC3C=CC4C=CC=1C=4C2=3<br />](https://www.chemicalforums.com/SMILES/ca3ceec8177c6be26590.png)
![<br />C1=CC2C=CC3=CC=C4C=CC1=C4C=23<br />](https://www.chemicalforums.com/SMILES/8e358c2fbd77ae94b116.png)
![<br />C1=CC2=CC=C3C=CC4=CC=C1C4=C23<br />](https://www.chemicalforums.com/SMILES/0dcdf1a595860d9c92e6.png)
Now my problem is estimating the dominance of each form. Are they equal or is there one which is more dominant?
This is what I’ve got so far:
Rules for estimating stability of resonance structures- The greater the number of covalent bonds, the greater the stability since more atoms will have complete octets.
- The structure with the least number of formal charges is more stable.
- The structure with the least separation of formal charge is more stable.
- A structure with a negative charge on the more electronegative atom will be more stable.
- Positive charges on the least electronegative atom (most electropositive) is more stable.
- Resonance forms that are equivalent have no difference in stability and contribute equally (eg. Benzene).
Pyracyclene has the same carbon atoms, the same number of covalent bonds and a formal charge of zero. I don’t see any difference in stability either. So it seems that all forms are equivalent.
Is this correct?