Thursday, September 1, 2011

The role of theory in chemistry

I just read a nice article Theory in Chemistry by Roald Hoffmann. Although, written in 1974, I consider it just as poignant (or perhaps even more so) today. It should be read in full. But here are a few highlights to motivate you to read the 3 pages.
Is not the design and analysis of a beautiful experiment theory?
Given the human character, rationalisation poses no problem. Prediction is another matter. By and large, theory has not predicted much chemistry.
some exceptions.... I would call a credibility nexus - in which a group of experimentalists, otherwise skeptical of theory, suddenly found itself faced with the success of a simple theory. That set of specialists quickly became concerts, often zealots... 
the most important role of theory in chemistry is to provide a framework in which to think, to organize experimental knowledge
Hoffmann identifies six examples of "credibility nexus"
  • Huckel's rules for the stability of different conjugated organic molecules
  • Walsh's rules (1953) which showed how the geometry changes in excited states of polyatomic molecules could be derived from simple symmetry and bonding diagrams
  • Huckel theory descriptions of the spin distribution in anion radicals
  • crystal field theory for transition metal complexes which led to a renaissance of inorganic chemistry
  • critical phenomena
  • orbital symmetry conservation [for which Hoffmann later received the Nobel Prize]
I came across the article via a review article, "A Different Story of pi-Delocalization" by Shaik, Shurty, Davidovich, and Hiberty who claim that valence bond theory provides a  "credibility nexus".

1 comment:

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