Tuesday, February 9, 2010

Marriage counseling for chemists

Roald Hoffmann, Philippe Hiberty, and Sason Shaik are probably my three favourite theoretical chemists. They write beautiful papers which focus on the quantum mechanical basis for chemical concepts and understanding rather than computation. Being a fly on the wall when they are all in one room for a scientific discussion would be fascinating. Well I don't have to dream. There is a really nice paper in Accounts of Chemical Research, A Conversation on VB vs. MO theory: a never ending rivalry. The three discuss and argue the relative merits and relationship between valence bond theory and molecular orbital theory. Here are a few choice quotes:

RH: A standard technique in marriage counseling (and I do think that MO and VB are a partnership) is to have the two parties stop and repeat, with an effort at understanding, what was said by the other partner. Can we try that? ......

PH: .......Pauling was smart enough to disguise all these “physical” elements of VB and packaged it as simple resonance theory. This was good for the 1930s, but now chemists have more theoretical savvy, and can digest these bits of physics, couldn’t they?

RH: Maybe. Some of them think theory is computation, and dignify that with the name of physical insight. The best physicists I’ve known - people like Ed Purcell - were after a quality of understanding that is ... almost chemical.

SS: ........ what tipped the balance in favor of MO may have been simply the computer implementation of MO-based theories. Chemists are a practical lot; they simply went where they could calculate.

RH: As they are doing now with the software available - it’s amazing what gains prominence just because there is a button in Gaussian to do it!

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