- There is a long-standing problem in the philosophy of chemistry arising from the fact that molecular structure cannot be strictly derived from quantum mechanics.
- Two or more compounds which share a molecular formula, but which differ with respect to their structures, have identical Hamiltonian operators within the quantum mechanical formalism.
- As a consequence, the properties of all such isomers yield precisely the same calculated quantities such as their energies, dipole moments etc.
- The only means through which the difference between the isomers can be recovered is to build their structures into the quantum mechanical calculations, something that is carried out by the application of the Born-Oppenheimer approximation.
- I agree that chemists view bonding in a more realistic fashion and may consider bonds to be in some senses real, while physicists may consider bonding in more abstract energetic terms.
We learn from Scerri that quantum mechanics does not distinguish between isomers like C2H5OH (ethanol) CH3OCH3 (dimethyl ether) with vastly different chemistry from different bonding and so must be complemented by some form of expertise, which differs between chemists who seek explanation in some real terms and physicists satisfied with something purely abstract.
RealQM is a new form of quantum mechanics in terms of classical continuum mechanics as a system of non-overlapping charge densities with direct physical meaning in 3d space, which meets a chemist's demand of a reality. In RealQM the formation/bonding of a molecule can be simulated which can make a distinction between isomers without need of expertise. The window opened by RealQM is explored in posts on Real Quantum Chemistry.
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