There’s the framework of the molecule superimposed on this map, and that triangle on top there, on the right, is what we’re looking at. Now, can we understand that, from the point of view of molecular orbitals, of Schrödinger’s equation why it should look like that in this particular case? So would a computer’s molecular orbitals provide understanding? So I was just showing you, as the class assembled, how you get these molecular orbitals, and I was showing you some of them. They don’t lie on the line between the nuclei. So that bond isn’t there in the electron density, the difference density. Professor Michael McBride: And one bond is missing. Student: And there’s another bond that’s missing. Professor Michael McBride: Some of the bonds are bent, and what else? And you remember what’s funny about it? What’s pathological? Dana? We looked at a cross-section through those three atoms, and it looked like that in the electron difference density. Right? When we were looking, we looked at this molecule and said that the bonding, from the Lewis point of view, was pathological. Okay, so let’s see if we can understand some of the things that we didn’t understand when we were looking at the molecule really, with X-ray diffraction. You’re a chemist, and your goal is to understand things let the computer do the heavy lifting mathematically and you understand it. But you’re neither the molecule - well you are a molecule - but you’re neither the kind of molecule we’re studying, nor are you a computer. You can’t do it absolutely, but you can, depending on how much computer power you want to throw at it, you can do it close enough for most purposes. Right? And the goal of the computer is to approximate the Schrödinger equation. Or we can do a computer calculation, and if we do a careful enough computer calculation, we can get something that we believe is pretty close to reality, like the total electron density I showed you. We can look at the real molecule, for example, with X-ray. Professor Michael McBride: Okay, so now we have a number of different perspectives we can take on understanding what holds molecules together that is, on bonding. Introduction: “Pathological” Bonding in the BH 3 Freshman Organic Chemistry I CHEM 125a - Lecture 15 - Chemical Reactivity: SOMO, HOMO, and LUMOĬhapter 1.
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