Frothing at the Brain

Stoking my ego is a great Christmas present. If you read and enjoyed any part of the Advent calendar, please comment here and say so, so that I will be happy and know my effort was worthwhile.

Well, it’s the 24th of December, the last day of Advent. We’ve looked at some of the fundamentals of organic chemistry: bonds, functional groups, resonance (“shuffling electrons around”), aromaticity, chirality, conformation (shape) and stability, along with some other aspects of chemistry like ionic bonds and phases of matter.

Today’s molecule, to finish the adventure, is something I learned about this month which seems very appropriate for the eve of a major feast.
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Today, it’s time for something a bit silly.

This is the second-best pun in the whole of chemistry: arsole, pronounced exactly the way you think. Arsole is actually its correct systematic name. I mean, it wasn’t called that for a joke. If you apply the international naming rules, arsole is what you get for this molecule.

The ‘ars’ comes from arsenic, symbol As. Arsenic is of course poisonous, although not actually very poisonous. You need quite large doses to kill someone. It’s usually classified as a metal, but in this molecule it forms covalent bonds. Covalent bonds aren’t the preferred kind of activity for metals, which tend to favour ionic or coordination interactions. Arsenic, if you look at the periodic table, sits in the borderlands between the transition metals (iron, copper, nickel and so on) and the nonmetals (carbon, oxygen, nitrogen and their ilk). Like silicon, it’s a halfway house and can behave like either kind of thing.

The ‘ole’ part of the name comes from the double bond. It’s short for olefin, meaning ‘containing a double bond’. Alkenes and benzene rings, as we’ve seen before, contain double bonds, but because of the simplicity of them – they only have carbon in the ring – they can be more precisely classified than olefins. Alkenes are olefins, but not all olefins are alkenes.

The best pun in chemistry is a derivative of arsole in which a benzene ring is fused to one side: benzarsole.

Edit: Eeep, sorry for the insufficient care and attention. The excessive picture size is fixed now.

We’ve covered two popular recreational drugs, ethanol and caffeine, so let’s look at a third. Nicotine is the major active ingredient in tobacco, and is usually ingested by burning tobacco leaves and inhaling the smoke. The nicotine is absorbed through the membranes of the mouth and throat straight into the blood stream, for an immediate effect.

Nicotine is highly addictive and very hard to shake a dependency to. Unlike caffeine, to which you can form a dependence within a week but lose that dependency just as fast, giving up nicotine takes months of determination.

There are numerous products on the market designed to ease the addiction-shaking process. These all work in the same basic fashion. A dose of nicotine is administered, to be absorbed through the skin or the membranes of the mouth, without the accompanying tobacco. This way you can lessen the cravings without surrendering to the temptation to smoke.

My own suspicion is that these non-smoking nicotine sources only help some people. Remember, it’s the nicotine that’s addictive, not the smoke, so the aids are addictive too. For some people, gritting their teeth and going cold turkey is likely to work best. For others, gradual dosage reduction will be easier.

It’s also worth noting that, nicotine aside, smoking is really bad for your health. Nothing that fills your lungs up with tar is good for you. Transferring a nicotine addiction to patches or gum rather than smoke will be good for your health even if you can’t shake the addiction itself.

Yesterday we took a whirlwind tour through liquid crystals. Today, let us consider another strange phase of matter – glass.

Technically speaking, ‘glass’ is actually the name of a phase just like ’solid’ and ‘gas’ are phases, but in common usage glass means a mixture composed mainly of silicon dioxide.

Silicon dioxide, often referred to simply as ’silica’, is what chemists call “isoelectronic” with carbon dioxide. It has the same number of electrons in equivalent orbitals, because silicon sits just below carbon in the Periodic Table. It’s in the same group, so has some of the same properties. But silicon dioxide is a solid at the surface temperatures of Earth. It makes up the vast majority of the Earth’s rocks, and therefore of the Earth.

Glass isn’t, as is commonly thought, a supercooled liquid. It’s a non-crystalline solid. Silica takes on a lot of forms, including several crystalline arrangements, and glass is its amorphous solid form. It’s both brittle and rigid, so it really can’t be considered a liquid. It doesn’t have a normal phase transition when it melts – it looks like a continuous softening rather than a distinct transition to liquid – which is where the confusion comes in.

Crystals form when a material cools and becomes a solid. In effect, the material freezes. But crystals aren’t all the same size. The faster you cool something, the smaller the crystals will be, which is why ice-cream made very fast is the best kind. If you cool some things, like silica, fast enough the crystals are so small they don’t exist.  Molecules have to arrange themselves in strict order to make crystals and if you cool them fast enough, they don’t have time to line themselves up before they’re too cold to do it. The resulting solid is non-crystalline – in some cases, it’s a glass.

This is 4-cyano-4′-pentylbiphenyl, and it’s a liquid crystal.

Now, to cover liquid crystals properly would take up another Advent’s worth of posts, so I’m not going to. I’m going to simplify things horribly. I’m going to tell you lies-to-readers, in the same way that teachers tell lies-to-children. I know it’s not precisely correct, and you know it’s not precisely correct, but it will serve to get the basic concepts across.
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