Friday, December 14, 2012

Ecce LUMO


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:

HOMO/LUMO
Donor/Acceptor
Base/Acid
nucleophile/electrophile
Plug/Socket
Hand/Glove
Foot/Shoe

You can guess the rest.

2 comments:

  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?

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  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!

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