All of chemistry was now re-forming itself in Pauling's mind. Like a jazz musician,
he was taking themes suggested by quantum mechanics and improvising on them, drawing
from his growing library of known molecular structures (much of it from his own x-ray
crystallographic studies) and guides like Pauling’s Rules and the electronegativity
scale. His was a new kind of chemistry that played in the spaces between the old categories.
Pauling's quantum chemistry was not either/or: either this or that orbital, either
ionic or covalent bonds, either single or double links. Pauling's chemical bond was
a fluid, multiform thing that often resonated between different forms. This was exciting,
beautiful chemical music, and he was the first to play it.
The last in his chemical bond series, "The Nature of the Chemical Bond VII. The calculation
of resonance energy in conjugated systems," again written with Jack Sherman and published
at the end of 1933, demonstrated the power of Pauling’s unique approach. In it, he
explored a range of conjugated systems (molecules in which double and single bonds
alternate in a hydrocarbon chain — examples include a number of biochemical compounds
like the carotenes and lycopene) and aromatic groups. Pauling and Sherman concluded
the paper with a set of rules for the structures and properties of conjugated systems.