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Alrighty, so even though this is going to be several days late, *hides in shame*, I finally found some downtime to type up some of the most fundamental rules to naming organic compounds.  To be honest, the entire idea of nomenclature wouldn’t be so bad, since IUPAC (International Union of Pure and Applied Chemistry) did a mighty fine job-ish of coming up with a good systematic way to name compounds.  Unfortunately, as it is with everything in chemistry, it is never that easy.  To put it the way Professor Glatzhofer did: “The first three pages of the IUPAC text, which is about three times your text book, is all you’ll ever really need to know about nomenclature.  The rest is the exceptions.”  Gee, thanks.

Yes, so not only does the IUPAC naming system have its own little twists and turns on the rules, we also have common names.  Obviously, these are the names that we used for compounds before IUPAC came along and created a giant rule book.  Nevertheless, the simpler compounds are rather easy to name and follow a comfortable step-by-step process.  Yay! (Right?)

The Carbon Chain–First and foremost, we must identify what the base chain of the compound is.  Usually, this can be a 12 membered carbon.relatively easy as it just entails counting up how many carbons we’ve got.  Of course, it will get difficult when the chain branches into several units.  Just remember, the longest chain may NOT be the one that looks like a straight (if zig-zaggedy) line across the page.  Quite often, if the chain is branched, the longest chain will follow a branch.  Also, you can only number two ways: left to right and right to left.  For now, just number it left to right.  Now, how many carbons do you have?  The nomenclature goes as follows: methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane and so forth.

A derivative of this compound will become very useful to you in the future!There are two exceptions to this:  Is there a ring in your compound?  If yes, then you must use the ring as your base compound.  If there is more than one ring, use the largest one.  The naming follows the above pattern, just with a cyclo- prefix.  Does your compound contain a double or triple bond?  Then drop the -ane and add -ene or -yne respectively.  Are there branches of C chains coming off your main chain?  Then count the number of carbons and name it, then remove -ane and add -yl (i.e. methyl, ethyl, butyl…)

Easy, yes?  Great.  It gets better!

Simple Substituents on the Chain–Now of course, we would all love if everything was just a saturated carbon chain.  It never works out as such since substituents are the atoms we rely on to react organic compounds!  Let’s just do alcohols and halides for time’s sake, though I do plan to go into much further detail at some point in time (ketones, aldehydes, carboxylic acids, esters, ethers etc).  However, today is supposed to be a breif overview.  The rest will require their own topic…

Of course, an alcohol is an organic compound that contains an -OH group.  You, dear reader, will probably be quite familiar with ethanol, since that is the culprit in alcoholic beverages.  As you just saw, to name an alcohol, you drop the -ane, (-ene, or -yne) and add an -ol.  Simple, yes?

Halides are a bit different, as their nomenclature involves a prefix instead of a suffix.  We typically call them alkyl-halides and they are quite simple to name.  If there is a chlorine on your chain, you’d name it chloro-name (or boro, floro or iodo).

Putting it together–Alright, now you didn’t think you could just slap some -ol’s and boro-‘s on the name of your chain and get away with it scott-clean, did you?  Of course not, chemistry is never that nice.  You counted the number of substituents on your carbon chain for a reason, remember?

Now, in order to give someone who is reading the name of your compound enough information to actually draw/identify the Name that Molecule!compound, we must number its substituents.  Here it gets a tad tricky.  You want to number your carbon chain in the direction in which you get the smallest numbers. Ex: If I had this compound, the first thing I would do is count the number of carbons; the base chain is pentane.  Then, I would identify the fact that there is a chlorine group on the carbon chain, so I need to number as such that Cl gets the lowest number possible.  As it turns out, it is in the middle of the carbon and should be numbered as 3.  So, to put this together, the compound is named 3-Chloropentane.

If there is an alcohol somewhere on the compound, it gets numbering priority and you should number your base chain in the direThis one is trickier!ction that gives the OH group the smallest number.  So!  If we have this compound, we should first note that the carbon chain branches!  Lucky for you, however, the branches are the equivalent.  The only difference is that one methyl group comes out of the plane of the page, where as one goes into the plane of the page. So, when counting, we get 4 carbons, so our main chain is butane.  We have two functional groups here, an OH and a CH3 group.  The OH group has numbering priority so we must number such that OH gets the lowest number possible.  That gives us 2.  So we have 2-butanol so far.  Now, we must add the methyl group in.  It is on the same carbon as the OH group; therefore, we get 2-methyl-2-butanol!

Lets do one last example, one that takes into account what happens if we have two of one substituent.Name this Compound! Obviously, we only have one carbon, so this is a methyl compound.  Now, we have two Chlorines and and two Flourines.  I said that things need to go alphabetically, right?  Well, what happens when we have two functional groups that start with the same letter? (Dichloro and Difluoro)  Well, we remove the di- and we alphabetize that way. So, here we have dichloro-difluoromethane.

So, how was that for a brief overview of nomenclature?  Not very brief, eh?  Well, I hoped you all enjoyed this and you have a better understanding of the basic ways in which we name organic compounds.

Happy Chemistry!

The Alchemist Kitten