Friday, August 29, 2008

trans - on the other side of what?

Well, as usually happens, I was reading something and found something else. And it was kind of interesting, so I thought I would post about it.

So you hear every so often about this prefix "trans" especially when it precedes "fat"... and you've heard it was "bad". And you may have wondered what "trans" means, and where it comes from, and what the "good" kind are called.

If you look up "trans-" you would find that it is an English prefix, coming from a Latin preposition trans, which means "on the other side of". It comes up in compounds like "transatlantic" but even in older words like transmit or transport or translate or transfer, with more Latin roots meaning "send" or "carry" or "bear" (the verb, not the animal... I will omit the traditional joke here). But what can it mean in connection with something like "fat"?

The answer is Bond. Double bond. (hee hee)

Double bonds between carbons, which occur in "unsaturated" fats - that is, those fats which don't have all the hydrogens they could have. (You used to hear the margarine commercials talk about "polyunsaturated fats"!) Those that have as many hydrogens as possible don't have any double bonds, and are called "saturated" - these are componds like lauric, myristic, palmitic, and stearic acids. All very weak acids, and found in things like lard or beef fat. They happen to make very good fuels, but we're not going into that matter today. Then there are unsaturated fats like palitoleic, oleic, and linoleic acids, which contain double bonds.

Now, the typical bonds in chemical compounds are single bonds, and the things that are on either side of that bond are free (more or less, depending on other things) - free to rotate around that single bond. But not in double bonds! They are rigid, and the things on either side of that double bond are fixed relative to each other.

So, when things are on the opposite sides of a double bond, they stay there, as they cannot swivel around to come to the same side... That means these "trans" fats have double bonds where the other connections fall on the opposite sides of the double bond.

For example, here is trans- chlorobromoethylene. (These words just roll of the tongue of organic chemists, it's an art. Hee hee)

Very nice. As you can see, the chlorine (Cl) and the bromine (Br) are on opposite sides of the double bond.

Now, chemists and Latinists will know that there is another word for the opposite idea to "trans". It is the word "cis" which is Latin for "on the same side of"; you may have encountered the word "cisalpine" in a book about history - that means the area on the southern side of the Alps (the side closer to Rome). These two Latin prepositions (which both take the accusative, I am told, for those of you who like to know these things!) have their importance in chemistry even to this day. No joke.

And just to show you what that looks like, here is cis- chlorobromoethylene.

Also very nice. Now you see the chloro and bromo are on the same side.

Werll, I am a Chestertonian, and try to be interested in everything, but I also try to find humour in everything as well. And, as you probably have expected, there are some cute chemical jokes arising from these terms. There are two famous chemical compounds, not to be found in laboratories:

which of course you can see is cis-Co-Kid.

And then there is also this:

which goes by the common name of trans-Parent.

While there isn't any element with "Kid" as its symbol (at least at present, who knows what they'll discover next week), Co is nothing other than cobalt, a wonderful metal in the "transition triple" with iron and nickel. Pa is the symbol for Protactinium, which is radioactive. Please do not attempt synthesizing this in your home lab! But "Ma"? Well, oddly enough, there used to be an element called Masurium which is now known as Technicium (number 43) which is man-made and also quite radioactive.

(No, transparent things aren't really radioactive. Please don't call the NRC about your windows. Problems with windows should be referred to Mr. Gates.)


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