In his book on molecular orbital theory, Molecular Orbitals and Organic Chemical Reactions, Ian Fleming notes that Pauling formulated an early alternative model to Huckel theory for explaining the bonding of simple conjugated polyenes. Evidently, this came to be called $\tau$-bonding. Fleming describes it as a modification to, or offshoot from, the hybridization model, in which orbitals similar to sp3 hybridized orbitals are combined. Fleming says that the $\tau$-bond model makes the extent of the conjugation less obvious, but that the model
[...] might have some virtues, not present in the Huckel model, especially in trying to explain some aspects of stereochemistry.
I don't have access to the relevant primary literature, and the treatment of the subject in Fleming's book amounts to one paragraph with an accompanying diagram. A search online was relatively fruitless.
My questions are:
- Is $\tau$-bonding just the historical precursor to the bent/banana-bond model, or does it have some unique independent significance that makes it directly relevant to modern chemists?
- What are the specific "virtues" that Fleming might have been referring to, and what, if any, advantages does the $\tau$-bond model have over Huckel theory and/or other approaches grounded in MO theory?