Part 5: The Chem in SpaceChem - Round 2
The Chem in SpaceChem, Round 2Note: As The Chem in Rounds 1 – 4 were written after the tournament, they may refer to later rounds.
4: Counting to 100
Inputs: Θ-diazene
Outputs: Fermium
Diazene, N2H2
Melting point: Unknown
Boiling point: Unknown
Molecular mass: 30.03 u
Density: Unknown
No theta, so let’s talk about regular diazene. It has a structure of H-N=N-H, but because each N has two leftover electrons (‘lone pairs’), the H’s can either point up or down. This gives diazene 2 stereoisomers, one with both H’s to the same side (cis), one with them opposite (trans).
Diazene does exist, but it’s a very unstable compound that quickly reacts to N2 and hydrazine (N2H4). That’s why I have no melting/boiling information listed. It is most probably a gas at room temperature, and there are some predictions floating around for the temperatures, but I don’t really trust any of them.
In any case, it is sometimes prepared in the lab and then immediately used for certain organic chemistry reactions. It can break down many alkenes (double bonded C’s) and alkynes (triple bonded C’s) to single bonds, without breaking other functional groups. Because of the reaction mechanism, only cis-diazene can do so, but that’s no problem because as cis-diazene is used up, the trans form will slowly switch to the cis shape.
Fermium, Fm
Melting point: 852 °C, 1565 °F (predicted, according to Wikipedia)
Boiling point: Unknown
Atomic mass: 255 or 257 u
Density: Unknown
Fermium, element number 100. Elements this high in the table are not stable, and the most stable isotope of Fermium, Fm-257, has a half life of about 100 days. Any naturally formed Fermium on earth is long gone. It was first discovered in the debris of the first hydrogen bomb test, Ivy Mike, and named after Enrico Fermi, the physicist who built the first nuclear reactor and is named as one of the ‘fathers of the nuclear bomb’.
Atomic mass (and by extension, molecular mass) is defined by taking the average mass of the natural isotope composition. Fermium is not natural, so we can’t do that. The most common isotopes weigh about 255 and 257 u, so I listed those. Fermium is the highest element that can be formed by a process called neutron bombardment, instead of by shooting heavy nuclei at each other. Neutron bombardment allows for making ‘macroscopic’ quantities, that is whole nanograms or perhaps even micrograms at once. Heavier elements than this usually don't come in more than a few dozen atoms at once.
It is likely that Fermium is a solid metal at room temperature. However, because of the radioactivity and the way this stuff is prepared, it was never made as a solid metal. All chemistry experiments were done with dissolved Fm3+ and Fm2+ ions. Fm3+ can form complexes with a lot of organic molecules, and it can also form complexes with some anions such as chloride and nitrate.
It is well possible that it could do some very interesting chemistry, but we will never know, as the Fm-nuclei are too unstable and dangerous to do lengthy experiments.
Feasibility of the reaction
Feasibility: Low.
We’re talking about fictional compounds and about nuclear reactions. Both are a big no here. Although, other than theta we have Hydrogen at our disposal, and it’s worth noting that if we go back far enough, every single atom in the universe started out as a hydrogen nucleus.
---
5: Three
Inputs: Isocyanic acid.
Outputs: Cyanuric acid.
Isocyanic acid, HNCO
Melting point: -86 °C, -123 °F
Boiling point: 23.5 °C, 74.3 °F
Molecular mass: 43.03 u
Density: 1.14 kg/L
Isocyanic acid, H-N=C=O (yeah, it's wrong in the puzzle) is a rather unstable compound. It can be formed by protonation of cyanate (NCO-) salts. It hydrolyzes to carbon dioxide and ammonia, and at high concentrations it tends to polymerize into cyanuric acid and cyamelide (a large polymer). Isocyanic acid can be kept for a few days in a freezer, but it is also found in cigarette smoke and smog, where it can cause a health risk to the lungs. Some organic reactions are known, but I think the substance is not used much, because of its instability.
At low temperatures, a small amount of isocyanic acid will be in another form, the tautomer cyanic acid (NCOH, with a triple bond between the C and the N). The proton (H+) is on the other side. Interestingly, cyanate salts do not have this tautomerism, because in the crystal lattice there’s always multiple cations at multiple sides associated with each cyanate anion.
Another structural isomer, one that does not form from isocyanic acid by itself, is fulminic acid, HCNO. The fulminate ion is friction sensitive and tends to decompose explosively.
Cyanuric acid, 1,3,5-triazine-2,4,6-triol, 1,3,5-triazinane-2,4,6-trione, C3H3N3O3
Melting point: Decomposes at 320 °C, 608 °F
Boiling point: None
Molecular mass: 129.1 u
Density: 2.5 kg/L
You might’ve noticed that those two systematic names refer to different compounds. That’s correct. They are tautomers, just like isocyanic acid and cyanic acid. The H’s can be on the O’s (then there’s three double bonds within the ring) or on the N’s (in which case the O’s are double-bonded to the C’s). In solution, the triol predominates.
Cyanuric acid is a stable, white, odorless powder. It can be synthesized from urea, and is used directly or as a precursor for other compounds in bleaches, disinfectants and herbicides. It is also sometimes used as a nitrogen-containing additive in pet foods.
Interestingly, by itself it is not toxic, but when it gets in contact with melamine, it forms an unusual complex sometimes called melamine cyanurate (cyanuric acid, in this case in the trione form, is red):
The dashed lines are not covalent or ionic bonds, they are hydrogen bonds (so the cyanurate name is technically wrong). In this case, they are strong enough to keep the molecules together, similar to the structure of DNA. Each molecule can form bonds like that in three directions, forming a big network. This complex forms strong crystals, and is more toxic than either melamine or cyanuric acid. The crystals clog the kidneys, forming kidney stones and causing acute kidney failure. In 2007, pet food was recalled and in 2008 there was the Chinese milk scandal, which I talked about in Closed Tournament Round 2. Both had to do with kidney failure caused by melamine, but there is evidence that most of the troubles were caused by melamine cyanurate.
Feasibility of the reaction
Feasibility: High.
As I said, at high concentrations, isocyanate does polymerize to cyanuric acid and larger compounds. This reaction isn’t very hard.
Reaction energy: Exothermic, about 600 kJ/mol
A somewhat rough estimate, as there are different numbers listed. By the way, this is going from gas isocyanic acid (liquid isn’t listed, and this reaction would probably take place above 23 °C anyway) to solid cyanuric acid, so the heat of vaporization is included. From gas to gas, it would be about 460 kJ per mole.
We’re going from an instable molecule to a stable, possibly somewhat aromatic (three double bonds in a six-ring) compound. It makes sense our product has less energy, which makes the reaction exothermic.
---
Challenge 2: Precious Oxygen
Inputs: Silver, Gold.
Outputs: Oxygen.
I have discussed all three elements already, oxygen in Round 8, and silver and gold in Closed Tournament Round 4. But I have more to say about oxygen.
Oxygen
I’m going to talk a bit about the less known form of oxygen. I don’t mean ozone, O3. I mean another form of O2, known as singlet oxygen. To explain this, I need to go a bit into quantum chemistry, one of the most complicated but also one of the most useful ways to think about chemical bonding. If you don't care about the details, skip to the bolded instance of 'singlet oxygen'.
I'll have to simplify here, which, as always, will bring some inaccuracies. In any case, in quantum chemistry, we describe electron position and momentum with something called a ‘wave function’. Basically, it is a mathematical tool to calculate the probability the electron is at any one place. It is important to note that this function does indeed behave like a wave. When waves come together, they can either strengthen each other (make it more likely to find an electron there) or cancel each other out.
The places were electrons can be around an atom are called ‘orbitals’. Up to two electrons can fit in each unique orbital, and orbitals are always filled from lowest to highest energy (from closest to the nucleus to farther away).
When atoms bond to form molecules, this can be described by simply adding the wave functions together. This way, we get a new set of orbitals, molecular orbitals (MO’s). Every combination of 2 atomic orbitals (AO’s) makes two MO’s, one with a lower energy than the AO’s (if the wave functions strengthen each other), one with a higher energy (if they partially cancel each other out). A bond will form if electrons can drop into a lower orbital, so those MO’s are called ‘bonding orbitals’. The higher energy ones are called ‘anti-bonding’, but if there’s enough electrons, they will be filled up anyway. This gives us a way to calculate how many bonds there are between a pair of atoms.
For instance, the oxygen molecule has 12 electrons total. Two electrons fit in each orbital, so we usually talk about electron pairs in this context. As it happens, for oxygen, there are 4 electron pairs in bonding MO’s, while there are 2 in anti-bonding MO’s. 4 – 2 = 2, so the calculation says the oxygen molecule has 2 bonds between the atoms. And our measurements tell us that’s true.
Now, at the highest occupied MO for oxygen, there is actually another MO with exactly the same energy. Normally, the electrons up there like to sit far away from each other, so there’s only one electron in each of those two equal-energy orbitals. Because of reasons I won’t go into, this is normal state is known as triplet oxygen. Oxygen is rather reactive, as we all know, but those unpaired electrons actually reduce reactivity quite a bit.[1]
With quite a bit of energy (93 kJ/mol), it is possible to push those antisocial electrons together in one MO anyway. In that case we get singlet oxygen. Because of more ‘quantum’, singlet oxygen will not jump back to normal oxygen right away, it takes an hour or so. There are several ways to make singlet oxygen. Some chemical reactions of bigger molecules will have it as a product. Chlorophyll and other molecules involved in photosynthesis tend to release singlet oxygen as well.
Singlet oxygen is very, very reactive. It can react with organic compounds in ways normal oxygen can’t. The stuff is used to exterminate heavy infestations of pests in buildings. It’s also used to kill cancer cells in a certain kind of therapy. It is one of the more toxic contents of photochemical smog, and the damaging effect of sunlight on organic materials is often caused by singlet oxygen.
It damages humans too, although there are certain molecules in our cells that can stop the stuff. Singlet oxygen can be used for certain organic chemistry reactions, but I don’t know if this is common or not.
Feasibility of the reaction
Feasibility: Low.
Nuclear. Nope.
---
[1] Shriver & Atkins - Inorganic Chemistry, Fourth edition