Friday, December 14, 2012


Ecce Homo, Caravaggio (1605)

Behold the HOMO (Highest Occupied Molecular Orbital), seeking reception;
Behold the LUMO (Lowest Unoccupied Molecular Orbital), offering reception.

Chemical reactions are electronic transfers. I don't mean electronic transfers like PayPal is (although there are similarities between electricity and money). I mean electronic transfers like oxidations and reductions, substitutions, proton transfers--which all involve electron donors and acceptors.  I still think that BH3NH3 best illustrates how chemistry is like sex: link

Presumably, the chemistry of memory has some donor and acceptor aspect at the molecular level. Long term potentiation. Learning is also like transubstantiation--words becoming neuronal flesh and all that. But there is more to learning than replication.  As Plutarch noted, learning is less like bucket filling and more like igniting little fires; Jefferson echoed that same thought: knowledge is contagious.

Here are some mnemonics for today's lesson:


You can guess the rest.


  1. When Bohr first proposed that electrons jumped from orbit to orbit say in atomic orbitals (analogous but simpler than molecular orbitals like HOMOs and LUMOs), he was challenged by Rutherford: how would the electron "know" where to go and where/what is it in transit?

  2. Rutherford was thinking: sure you can knock an electron into a higher, more distant orbit, but how does the electron "know" what distance and energy to select? In his mind it was like goosing a satellite's orbit. Bohr's answer was that only orbits having integer values were "allowed"; an electron wouldn't take on half the energy to get to the LUMO state; the LUMO demanded the whole integer!