But oftentimes theoretical chemistry is not as important as what we get out of experiments because unlike physics, which attempts to derive general laws of nature, chemistry has to deal with the nitty gritty of the diversity of actual miscroscopic interactions of things. Any theory that is not entirely rigorous or even has slight room for an exception will be ignored by necessity, and physics is chock full of such examples. Biology is in a certain sense better (since it deals with larger things) and in a certain sense worse (as it relies on dogma and mysticism, at its essence, to explain the systems of life), and still nobody has gone beyond Aristotle and Kant in giving anything close to a rigorous definition of life as such.

All this computing power. Can we even simulate a water molecule yet from scratch with QM?

Physical Chemistry (I think it was Chem 361 at UofI) took most of the semester to get to the point where we could derive the shape of the hydrogen orbitals. Probably the best lecture of that class.

As you move up levels starting from physics (eg. physics-> chemistry-> biochemistry-> biology), each layer has several "laws" which are generally pretty established, but a causal connection between the layers is hard to provide satisfactorily. And that is how I think it'll always be, else we'll be expecting to explain Shakespeare's plays using physics.

Also, this is where Rutherford's "all science is either physics or stamp collecting" holds a lot of water. As you move up the science layers, the laws themselves become less mathematically rigid until by the time you get to the social sciences, explanations are all hand-waving, and all "laws" are statistical at best and empirical.

And also emergent behavior means that at each level, we need different abstractions to deal with the problem. Even with chemistry, there's ideas like benzene rings that are aromatic, you couldn't predict that from particle-particle interactions. So it's not just that it's hard to understand quantum mechanics, it's that understanding QM doesn't mean you'll understand the problems that chemistry deals with.

As a chemical engineer, one of the signs of maturity was myself and each of my classmates individually coming to accept and embrace the inevitable “magic coefficient”.

The curious always wanted to know why some magic coefficient was there. Where did it come from? How is it measured / calculated? How to derive the magic coefficient?

Eventually you learn that it’s turtles all the down. You can pick apart the magic coefficient and dive into the nuanced physics that its derived from…but then you still end up with a new magic coefficient.

So eventually, the curious students learn that the mysteries are out there for when you want to go out and explore them. But otherwise, we pick our level of abstraction for the problem we’re currently working on and accept the magic coefficients that apply to that level of abstraction.

The real trick is knowing the conditional boundaries when those magic coefficients no longed apply and you either need different ones or “here be dragons”.

Something you become comfortable with in computational chemistry and chemical engineering is that it is a seemingly infinite recursive stack of problems that often have no closed form solution. Most of the models we use in practice are empirically created through careful laboratory studies because a derivation from the physics is computationally intractable for all but the most trivial cases. This leads to phenomena like getting different numbers for the same thing depending on how you compute and derive them.

There are multiple approximate models for the same thing. Part of the skill is choosing a model likely to produce results that map closely to the real-world in a particular context with the least amount of effort. Chemical engineering as a discipline is effective at navigating and constraining the internal inconsistencies of these myriad models in a tractable way.

The sausage factory is real. There isn’t a tidy bit of theory or math under this that is useful in real settings. This partly explains the handwaving nature of the explanations if working in that sausage factory isn’t going to be your profession. Even if you wanted to understand the theoretical basis, that becomes extremely non-trivial very quickly, so it isn’t the kind of thing worth spending much time on if you aren’t going to go deep in it.

Not a satisfying answer, I know.

You had a poor organic course. Even orgo 1 should have you thinking about resonance + electron-rich or -deficient areas of molecules and how those lead to reactions.

I was lucky enough to have Morrison and Boyd as my undergrad ochem textbook. they built the material up really well from first principles.

And people clutch their pearls at ai not really understanding anything when people describe university experiences and lessons like this...

> physics that predicts chemistry

Do we have this?

they are featured in collegeboard's course and exam description: https://apcentral.collegeboard.org/media/pdf/ap-chemistry-co...