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Section IV: Carbon Chains.




Before we get into the actual composition of the various fuels, we need to review a little basic chemistry on the construction of organic compounds, particularly petrol fuels.


99.99% of all petrol chemicals are comprised of exactly two atom types: Carbon and Hydrogen. Since the carbon is the more complex atom, and invariably the defining one in any carbon-hydrogen relationship, often it is the only thing depicted in chemical formula. In the chemicals above, the black dots represent carbon atoms. The blue dots represent Oxygen and the only hydrogens that are depicted are attached to the non-Carbon atoms.


Connectivity. Okay, this is where chemistry gets confusing for most people. They start talking about electronegativity, electron orbits, noble elements, etc. Fortunately, we don't need to go quite that deep. We're going to compress all that stuff into a simple formula: hands. Each atom has one or more hands, each hand can grab one (and only one) other hand, no hand likes to be empty, and for our purposes, no hand ever will be empty.


There are a LOT of atoms we could discuss, but we'll keep it limited to the ones above: Carbon, Hydrogen and Oxygen. Hydrogen only has one hand, once it's attached to something, it's done. That's why it rarely is the 'defining' atom in a molecule. Oxygen has two hands. When it grabs two Hydrogens, that's water, when it grabs another oxygen alone, that's what we breathe, and if it grabs a hydrogen and a carbon chain it makes alcohol. Carbon has four hands. This extra connectivity allows it to form infinite constructions and makes it the basic building block of life as we know it.


Now, let's look at a simple molecule, like Octane (above). It has eight carbon atoms connected by seven lines. Each black line represents a carbon hand linked to another carbon hand. So, if we look at just the top carbon atom, it has one hand in use attaching it to the next carbon atom, leaving three hands free. Those three hands are attached to Hydrogens that are not represented in the structure. The next one down has two black lines coming out of it representing links with two carbon atoms, leaving two hands free. This atom has links to two hydrogen atoms.


The Octane molecule forms the simplest Carbon "backbone" type. It has all carbon atoms, linked once each to another in the chain, and filled to the brim with hydrogen atoms. In chemical terms, it is a "fully hydrogenated" or "saturated" carbon molecule, and a cup full of these things would be an "aliphatic" compound that could be considered a "paraffin" for trade use. But more on that stuff in the next chapter.


Over to the right, we see the Octene molecule. Notice the double bond between the second and third atoms. Not only does it change the overall shape of the carbon backbone, but it reduces the number of hydrogens and changes the reactivity of the molecule at that point. This "mono-unsaturated" molecule is more biologically reactive, and therefore slightly more hazardous to the body than the Octane molecule. A cup of this would not be an "aliphatic" compound in the strictest sense of the term, though some would say so.


The second molecule, ethyl benzene, is an example of one of the more complex carbon-hydrogen atoms. It has a benzene ring which actively rotates three electrons in a highly reactive ring. Such rings are part of the "aromatic" group, many forming the wondrous variety of smells that the human nose can discriminate. These molecules are VERY biologically reactive and often poisonous in anything but very trace amounts. Also, they burn with particularly dirty by-products, sometimes more poisonous than the base chemical.


Finally, we have a couple of alcohols. The lower one, ethanol, is the familiar active ingredient in all alcohol intoxicants. The upper one is isopropyl alcohol. Often you can find this as "rubbing alcohol" and sometimes in high proof form as a paint stripper. Most of the alcohols are soluble in water, so instead of floating on the surface like the oils, they dissolve and dilute. So, unlike petrol fires, these can be successfully put out with water.


Okay, so, now you're an organic chemist. :) And more importantly, you're ready to delve into the variety of petrol fuels.


FuelBusters V: FuelComp


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