The powerful concept of resonance was now entering its full flower. The sixth in Pauling's chemical bond series, written in 1933 with postdoctoral fellow Jack Sherman, extended the concept to more chemical puzzles involving variations from classical single, double, and triple bonds. This work, too, was groundbreaking.

In "The Nature of the Chemical Bond VI. The calculation from the thermochemical data of the energy of resonance of molecules among several electronic structures" Pauling showed that molecules were not restricted to whole-integer links (the classic single, double and triple bonds) but could take on intermediate forms. Here again he melded the bond lengths and strengths from his ever-growing library of molecular structures with his ideas about the stabilizing influence of resonance, and came up with novel explanations for a whole slew of problems.

This was particularly important for structural chemistry. Atoms connected by single bonds were known to be able to rotate like wheels on an axle, for instance, while those linked by double and triple bonds were held rigidly and double bonds — with what he called "partial double-bond character" — were also restricted from rotating, an important factor in focusing the approach to potential structures and predicting new ones. In his sixth paper Pauling explained the restriction on rotation in quantum-mechanical terms, then applied his idea of resonance between single and double bonds to explain the bond lengths and rotational properties of a number of intermediate cases.