Alcohols Give Acids Wings*

Acids are sticky things -- they cling to each other and hardly break ranks. The reason why is called "hydrogen bonding." Alcohol loosens up acids, making them leave their own. Acids do bond with alcohols, but the combination is volatile esters.** That leads to flying apart.

Volatility --> wings --> nose (aroma).
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*The metaphor dates from (at least) Lord Kelvin. See my discussion here.

**The word "ester" is pure invention, without metaphor: link

Forces of Exclusion

Forces of exclusion are repulsive. Talking chemistry, it's called hydrophobia. Grease, for example, will not dissolve like salt does in the sea; instead it clots together, usually floating on top because it lacks the gravitas of water. And while grease is hydrophobic, it is lipophilic, a word that, like hydrophobia, also comes to us via Greek, rooted in the word lipos.

Lipids and water don't mingle. It's not that lipids are weak--they are very strong internally, giving us energy--they just lack enough polarity to part water like salt can. Salt ions actually direct water: cations attract the oxygen part of H₂O and anions attract the hydrogen part. These are electrostatic forces. They are intermolecular forces meaning between atoms and molecules:

While lipids have strong intramolecular forces, they lack intermolecular forces like hydrogen bonding in water (this also explains hydrocarbons' volatilities). Because lipids don't mingle with water, they appear to seek their own kind, separating out. But why don't they mingle with water? It's because they restrict water's freedom. They have no charge to slake. Most lipids don't hydrogen bond like water does:

Notice the orientation of white to red (hydrogen to oxygen, plus to minus),  H-bonding is an attractive force, not unique to water, but best exemplified by it. When a lipid or a hydrophobe enters the picture, the waters give up their ordered coziness and are forced to reorient around each hydrophobe to make what's called a cage--without enthalpic recompense as with a salt. Thus the exclusion is an entropic effect because it relates to physical law and order.

Portrait of an Enzyme

Enzymes "herd" molecules and accelerate reactions. They affect change, but do not themselves change. They exist in minuscule amounts, doing their work on more abundant molecules called substrates, building up new molecules or demolishing old ones, leaving behind smaller molecular fragments for further digestion. Enzymes cannot make the impossible happen--they just make the possible happen faster.

Enzymes bring together pieces and stabilize any awkwardness of the encounter.

Let me unpack that sentence. "Bring together pieces" means that enzymes gather pieces using available molecular forces--usually just simple repulsion and attraction--to orient molecules in space.

"Repulsion" usually means hydrophobia, but may also be simple blocking effects. "Steric" is a term of art relating to the latter effect. "Steric hindrance" means that my standing somewhere blocks you from standing in the same place--it's a repulsive effect. Enzymes use repulsive effects to restrict degrees of freedom to reduce the randomness of molecular encounters.

"Attraction" is more familiar. Enzymes deploy acids and bases within their active sites to spatially arrange substrates--they may use a base (negative) to attract and hold an acid (positive) on a substrate. Hydrogen bonding works similarly and is like a shared common interest.

"Stabilizing any awkwardness of the encounter" is the real key to understanding enzymes. This was Linus Pauling's idea.^‡ Enzymes don't just bring together and stabilize substrates--if they did just that their insides would soon clog up with unreacted substrates. They have to stabilize the awkward encounter--not just a roomful of substrates looking at each other.

Here's a visual of what I'm trying to say, taken from organic chemistry. Imagine that the enzyme's role is to surround and stabilize each of the following chemical species, but especially the one circled in red:

original

Stabilizing whatever's in the red circle brings down the height of the blue hump. That's acceleration.

Enzymes lure substrates together, polarizing and fostering attack. Polarize, attack, depolarize
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‡ See for example, link

"A single twig breaks easily but a bundle of twigs is strong"

That saying is attributed to Tecumseh, a Shawnee Indian chief, in the movie "Act of Valor."

I first heard the equivalent of that idea in the David Lynch movie “The Straight Story." Richard Farnsworth says (while demonstrating with sticks):

When my kids were young I played a game with them. I'd give each of them a stick. One for each of 'em, and I'd tell them to break it. They'd do that easy. Then I'd tell them to make one bundle of all the sticks and try to break that. And course they couldn't. I used to say that was family, that bundle.

I tried to extend that familial idea to hydrogen bonds: here

The US "mercury" dime—a stunningly gorgeous coin design from the 1930s and 40s—had a bundle of sticks on the reverse side:

1936 Mercury Dime designed by Adolph Weinman

The bundle was called a fascia after the old Latin term. I guess the notion of fascia had to be banished from  politics.

H Is For Humble Hydrogen

The sun consumes about a half billion tons of hydrogen every second, fusing mass into helium and radiating the excess as energy. We just sit back on sunny days and bask in the afterglow of the nuclear holocaust at a very safe distance, thinking nothing of it. Our nonchalance towards any solar dimming is justified by considering that the sun should last another 5 billion years or so.

Hydrogen fuel cells (chemical, not nuclear) are already used in spacecraft, and modern rocket engines burn liquid hydrogen and liquid oxygen. But back on earth, there is talk of using hydrogen as an energy source to replace hydrocarbon fuels. Hydrogen gas burns cleanly, as the very name reminds us: hydrogen = water generating; the catch is that hydrogen gas has to be made because little is found naturally on earth.

By far the cheapest way to make hydrogen gas is from natural gas, CH₄, using a process that co-produces CO₂ (the carbon atom has to go somewhere). But another little appreciated fact is that a big consumer of hydrogen gas is the fertilizer industry—hydrogen is used to make ammonia from nitrogen—and another big user is the food industry—it is used it to hydrogenate vegetable oils. Any large-scale diversion of existing hydrogen to transportation fuels will ultimately raise the price of food via the costs of ammonia fertilizer and food processing costs. Sound familiar?

What’s really needed is a new and different way to cheaply make hydrogen gas—something like the efficient photolysis of water or the electrolysis of water using electricity from nuclear power plants. Both technologies exist, but they are economic nonstarters. For my money, I’d rather see cars run on methane, rather than going through the additional process hoops of converting the methane to hydrogen gas. A similar argument holds for bio-fuels, which I will discuss when I get to carbon and oxygen.

Hydrogen is the most promiscuous chemical element, pair bonding with nearly every element and even forming special bonding threesomes called hydrogen bonds. Hydrogen bonds are the principle force binding the two strands of DNA together. Arguably, hydrogen bonds are present at the conception of human life: when the two single strands of DNA, one from the mother, one from the father, join for the first time, those strands are united by about 3 billion hydrogen bonds. Each one is worth a small amount, but together, summed over the entire double helix, amounts to a formidable binding glue.

The themes of family and weak and strong chemical forces reminds me of some lines from the David Lynch movie “The Straight Story." Richard Farnsworth says (while demonstrating with sticks):

When my kids were young I played a game with them. I'd give each of them a stick. One for each of 'em, and I'd tell them to break it. They'd do that easy. Then I'd tell them to make one bundle of all the sticks and try to break that. And course they couldn't. I used to say that was family, that bundle.