Proton Transfer

This time I will show a few "quantum images". Hydroxybenzoquinoline is kind of a cool molecule because it shows excited state intramolecular proton transfer. After UV excitation the proton is transferred from the oxygen to the nitrogen. This happens on a time scale of about 30 fs because the process is essentially barrierless. This is a time scale where you can do ab-initio molecular dynamics. And with modern LASER pulses you can also examine it experimentally. That's why these molecules have been rather popular recently.

What I want to show here are the orbitals because I think they look kind of cool. What you see are the two highest occupied orbitals (n, π) and the lowest unoccupied orbital (π*). The two important excitations are just between these orbitals leading to the ππ* and nπ* states respectively.

Related to the proton transfer it can be seen that the π* LUMO has more density on the N which increases its basicity to help it catch the proton.

Something else that is interesting is that a non-bonding orbital (coming from MO theory) really looks a lot like the free electron pair you would talk about in VB theory. I was arguing with an analytical chemistry professor once that he should not interchange the terms non-bonding orbital and free electron pair because they come from different approaches. Now I see that he was right but I did not believe him then because he was from analytical chemistry.

Enol (ground state)		Keto (ππ* state)
	π*
	π
	n

Just a short summary of the software: the orbitals are actually from semi-empirical DFTB. And the pictures are made with VMD.