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Chemistry: Organic Nomenclature

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  • Type: Video Tutorial
  • Length: 8:35
  • Media: Video/mp4
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  • Download: MP4 (iPod compatible)
  • Size: 92 MB
  • Posted: 01/28/2009

This lesson is part of the following series:

Chemistry: Full Course (303 lessons, $198.00)
Chemistry Review (25 lessons, $49.50)
Chemistry: Atoms, Molecules, and Ions (10 lessons, $16.83)
Chemistry: Chemical Nomenclature (3 lessons, $4.95)

As with previous chemical naming conventions, organic chemistry has its own nomenclature. Organic compounds are compounds with carbon. Hydrocarbons are compounds that contain only hydrogen and carbon in varying amounts. These are broken into three groups, alkanes, alkenes, and alkynes. Alkanes have an -ane suffix. Similarly, alkenes have an -ene suffix and alkynes keep the -yne suffix. Professor Harman teaches you the standard prefixes that are used to indicate the number of carbon atoms that are in each of the compounds. These include meth-, eth-, pro-, but-, and pent-. These prefixes also pertain to alcohols. Alcohols have an OH group connected to a hydrocarbon and can be identified by an -ol suffix. Once you know some of the common prefixes and suffixes, it is easy to identify characteristics of larger, unknown compounds.

This lesson is perfect for review for a CLEP test, mid-term, final, summer school, or personal growth!

Taught by Professor Harman, this lesson was selected from a broader, comprehensive course, Chemistry. This course and others are available from Thinkwell, Inc. The full course can be found at http://www.thinkwell.com/student/product/chemistry. The full course covers atoms, molecules and ions, stoichiometry, reactions in aqueous solutions, gases, thermochemistry, Modern Atomic Theory, electron configurations, periodicity, chemical bonding, molecular geometry, bonding theory, oxidation-reduction reactions, condensed phases, solution properties, kinetics, acids and bases, organic reactions, thermodynamics, nuclear chemistry, metals, nonmetals, biochemistry, organic chemistry, and more."

Dean Harman is a professor of chemistry at the University of Virginia, where he has been honored with several teaching awards. He heads Harman Research Group, which specializes in the novel organic transformations made possible by electron-rich metal centers such as Os(II), RE(I), AND W(0). He holds a Ph.D. from Stanford University.

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Recent Reviews

Nopic_tan
just what i needed
11/27/2010
~ dorothy4

excellent teacher, covering just what i needed and i can play it 1000s of times until i understand!!

Nopic_tan
just what i needed
11/27/2010
~ dorothy4

excellent teacher, covering just what i needed and i can play it 1000s of times until i understand!!

Atoms, Molecules, and Ions
Chemical Nomenclature
Organic Nomenclature Page [1 of 2]
With at least the beginnings of a systematic way of naming compounds in place for molecules, you’d think that when
we start to talk about organic molecules, organic molecules would just, in general, be molecules containing carbon,
that we could use the same set of rules. But no, chemists have not done that. In fact, a lot of the organic compounds
had been known and had names long before some of the other compounds. So there is a bit of a different
nomenclature system in place for organic molecules. So let’s take a little time and see how that works. And again,
what we’re looking for here is not memorizing names, but more looking for patterns in those names.
Now, if we look at a class of compounds called hydrocarbons, they are indeed compounds containing only hydrogen
and carbon. And we look, in particular, at a class called alkanes, and we’ll talk much more about alkanes later. But
alkanes would be carbons, hydrocarbons, where the carbon has as many hydrogens as possible. So these are often
referred to as saturated hydrocarbons. Now, we don’t understand yet at all what that means, or how we determine
whether something is saturated or not, so don’t worry about that yet. We will get there. Right now, I’m just describing
this as a collection of molecules having a general formula. In fact, we could make some sense out of this is if the
number of carbons was N, the number of hydrogens would be 2N plus 2, so, CH4, C2H6, C3H8. Now, I don’t care
about you knowing that formula yet. It doesn’t mean anything to you, so what’s the point? What I do want you to see
is that the names all end in –ane in this class. And, in particular, the number of carbons is dictated by the front end of
the word. So methane indicates that it has 1 carbon. Methane comes from cows. Lots of methane from cows, lots of
other places we get methane, also, underground mostly, but again, a 1-carbon hydrocarbon. Anytime you see that
meth-, that’s telling you it’s a 1-carbon molecule or a 1-carbon fragment connected to another part of the molecule.
Anytime you see –eth, on the other hand, like ethane, ethanol, ethene, we’ll get into, that indicates that there is a 2-
carbon fragment, or that the molecule contains 2 carbons. So again, you’ll notice the formula. We’ve got now 2
carbons. The next on the list would be pro- for propane, or propanol, or isopropanol. Anytime you see pro-, that’s
telling you again that you’ve got now a total of 3 carbons, either again in a fragment or in the overall molecule.
Propane you’re familiar with from propane fuel, for instance, like you would use in camping stoves. Butane, like in
butane lighter. If I can light it, there’s a butane lighter. Also, butane is a hydrocarbon, as well. It’s a 4-carboncontaining
hydrocarbon, though. Pentane, as you might expect, is a 5-carbon-containing hydrocarbon. So again, we
can go on to hexane, to decane and so on, but right now, let’s just focus on this first group of five, meth-, eth-, pro-,
but-, pent-. Those are telling us, again, the number of carbons.
So if we look at a related family of hydrocarbons, the alkenes, for instance, the alkenes sound very much like the
alkanes, but notice the different. If I look at ethane and ethene, the eth- tells me, again, that I’ve got 2 carbons. Look
at the formula. But notice that I’m missing now 2 hydrogens. And, in fact, for all of these cases, if I compare the
alkene and the alkane, I’m just missing 2 more hydrogens here. This is referred to as a class of compounds that are
unsaturated, meaning they could take additional hydrogens. And, if we gave them additional hydrogens, we’d get
alkanes. But right now, our focus is simply on how they’re named. And again, the key is that both propane, for
instance, and propene have 3 carbons. And that word or that prefix pro- tells us, or that root I should say, tells us how
many carbons we have. Thus, pentene would have 5 carbons in it. Notice again, all of these have an –ene ending,
indicating the type of family they belong to, the alkenes.
A third family of hydrocarbons would be the alkynes. A different ending again, -yne, fewer hydrogens still. Now notice
for ethane, ethene and ethyne, we’ve gone from 6 hydrogens to 4 hydrogens to 2 hydrogens. And so, again, these
are different compounds, but they share in common the fact that they have a total of 2 carbons. And that eth-, again,
is what tells us that.
Now, once you understand that, once you start to recognize anytime you hear these different roots that they’re
corresponding to simply the number of carbons, again, either in a fragment or in the molecule, you can start to make
sense of some really pretty impressive words. You’ll recognize these roots in all kinds of words in the ingredients.
This thing contains isobutane, 4 carbons. It contains propane, 3 carbons. It contains neodeconate, dec -, 10 carbons
in this case in that molecule. So a lot of information is embedded in these words, once you start to associate meth-,
eth-, pro-, but -, pent- with the corresponding number of carbons.
Let’s look at one other class of compounds, and that would be the alcohols. Now, alcohols, much more in this family
than just type of alcohol that you’re familiar with, the kind that you drink; that, actually, is ethanol. Eth-, right away,
tells us 2 carbons. –ol, the ending “ol”, that’s going to end up telling us that this molecule has an “O” connected to a
carbon and connected to a hydrogen. Now, we don’t know the first thing about bonding yet, so we’re not going to go
into much detail about this. But we will begin to recognize that anything ending in an “ol” is, in fact, an alcohol, does,
Atoms, Molecules, and Ions
Chemical Nomenclature
Organic Nomenclature Page [2 of 2]
in fact, share a common piece of chemical structure, and therefore behaves, actually, chemically in a very similar
manner. So ethanol and propanol, another example, in this case, isopropanol, that’s just rubbing alcohol. It is, again,
an example of an alcohol. That’s what that –ol ending tell us. Pro- tells us it’s at overall 3 carbons. And so, this is the
chemical structure of propanol. Notice there the 3 carbons, and here is the OH, telling is that it’s an alcohol. So
again, we can pull out pieces, at least of this – prefix iso- simply means that it’s different than something else. It’s
different than propanol itself, or normal propanol. And that would have this OH stuck on the end of the carbon chain,
rather than in the middle. Not important. The important part is “prop”, telling us, again, 3 carbons.
Estradiol, this is a female sex hormone. Do I have your attention now? Now, this guy is an ugly, huge molecule, but it
is 2 alcohols, diol-. And those are the 2 OH groups. So even in these big complex molecules, we can get information
about chemical structure. Even if we don’t understand everything about the molecule yet, we get little bits of
information. And, in fact, we’ll find that, chemically, estradiol acts very similarly, in some ways, to isopropanol or
ethanol, in that they are all alcohols and undergo certain chemical reactions that are very similar. Obviously, there are
big differences in these guys, too.
So, for right now, let’s just focus on these roots and what they mean, just committing to memory the idea that methmeans
1 carbon, eth- means 2 carbons, pro- means 3 carbons, but- means 4 carbons and pent- means 5 carbons.
And there’s many others, but these are certainly going to be the most common roots that you’re going to need to
understand to be able to make sense out of the names of organic compounds.

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