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The near-collision is even better than it looks, because it very nearly caused a real problem.

Spoken aloud in a noisy lab, "methyl" and "ethyl" differ by one consonant at the start of the word, and they name fragments that appear constantly, often in the same molecule. Anyone who has dictated a structure over a phone has had to say something like "methyl, M for Mary".

And "ethane" versus "ethene" versus "ethyne" is a second collision layered on the first — three different molecules distinguished by one vowel in the middle. Modern naming is precise and completely unsuited to being spoken, which is why chemists draw.

Your model is wrong, and pleasingly so — there is a hard limit and it has a name.

Every substance has a critical temperature. Above it, no amount of pressure will produce a liquid. Not a very large pressure, not an absurd one: none, ever. The liquid phase simply does not exist above that temperature.

So the answer for any particular gas is: look up its critical temperature and compare it to room temperature.

• Above room temperature — carbon dioxide, propane, ammonia — and yes, pressure alone will liquefy it. This is exactly why a propane cylinder contains liquid at ordinary temperatures.
• Below room temperature — nitrogen, oxygen, hydrogen, helium — and no pressure whatsoever will do it. These have to be cooled first, and for some of them cooled a very long way.

Hydrogen's critical temperature is around 33 kelvin, which is roughly minus 240 Celsius. Room temperature is not close to that, and the gap cannot be closed with a pump.

It is partly teaching and mostly real, and the honest answer has two halves.

Chemistry does have predictive theory. Thermodynamics tells you which products are favoured at equilibrium and it is quantitative and reliable. Quantum chemistry can compute a molecule's structure and energy from first principles to useful accuracy.

But which product you actually get is usually not decided by equilibrium. It is decided by kinetics — which pathway happens fastest — and the fastest pathway is often not the one leading to the most stable product. So the thermodynamic answer tells you where the system would like to end up and the reaction gives you something else entirely.

That gap is the real subject. Most of what a working chemist knows is about controlling which pathway wins, using temperature, solvent, catalyst, order of addition and concentration. Those are not fudge factors around a missing theory; they are the actual controls.

It is the double bonds sitting next to each other, not the ring size — and the specific problem has a name.

When a carbon has a double bond on both sides, that arrangement is called cumulated, and cumulated double bonds force the three carbons involved into a straight line. That is not a preference, it comes out of the bonding geometry: the central carbon's two double bonds have to point in opposite directions.

Now try to build a ring out of pieces that each insist on being straight. Four straight segments cannot close into a four-membered loop; you would need the corners to bend by ninety degrees, and the geometry does not permit it.

So the impossibility is not about four carbons and not about double bonds in general. Four-carbon rings exist perfectly well — cyclobutane is ordinary. What cannot happen is every carbon carrying two double bonds at once in a small ring.

"It is the exchange rate between the temperature scale and energy" would have saved me two weeks. Every appearance of R in an unrelated formula now looks like the same conversion rather than a coincidence.

Worth adding that both spellings of the first one genuinely exist in the literature — you will find monooxide written out in full — and that current recommendations lean towards not eliding as the default, precisely because unpredictable elision makes names harder to parse and harder to search.

The direction of travel in chemical naming for about fifty years has been away from euphony and towards mechanical regularity. A name that can be generated by a rule can be generated by software, and a name that can be generated by software can be looked up.

Monoxide survives that pressure only because it is entrenched in everyday language, safety labelling and legislation. It is a fossil protected by how many places it is already printed.

There is a mechanism worth naming because it makes the small solubility less mysterious.

When a salt does dissolve in a liquid metal, it often is not sitting there intact as ions the way it does in water. The metal can reduce the salt's cation — a reactive metal will simply take the chlorine and swap places, producing a different salt and releasing the other metal into solution.

So "does it dissolve" and "does it react" blur together in these systems in a way they do not in water. That is another reason the literature is thin and scattered: the answer depends on which specific salt and which specific metal, and half the interesting cases are chemistry rather than solubility.