Intertwingling the White-Cãlugãreanu-Fuller
and the Hückel Aromaticity Rules
- Hückel rule depends on phase shift; determined
by Lk and not by T.
Intertwingling: Lk(π) = T + W with 4n+2/4n
- Even Lk means no phase shift (all +ve β in determinant)
- Odd Lk means one phase shift (one -ve β in determinant)
Both systems will stabilize by minimising T (maximizing W)
Even values for Lk(π) → Hückel 4n+2 electron
ground state rule.
- Odd values for Lk(π) → Heilbronner 4n electron
ground state rule
An even distribution (=delocalization) of T around ring favours aromaticity
- Smaller T results in increased pπ-pπ overlap
- Larger W does not decrease β.
© H. S. Rzepa, 2007.