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Chemistry: Carbonyl-Containing Functional Groups


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  • Type: Video Tutorial
  • Length: 12:50
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  • Posted: 07/14/2009

This lesson is part of the following series:

Chemistry: Full Course (303 lessons, $198.00)
Chemistry: Organic Chemistry (8 lessons, $12.87)
Chemistry: The Functional Groups (2 lessons, $3.96)

This lesson was selected from a broader, comprehensive course, Chemistry, taught by Professor Harman, Professor Yee, and Professor Sammakia. 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.

Gordon Yee is an associate professor of chemistry at Virginia Tech in Blacksburg, VA. He received his Ph.D. from Stanford University and completed postdoctoral work at DuPont. A widely published author, Professor Yee studies molecule-based magnetism.

Tarek Sammakia is a Professor of Chemistry at the University of Colorado at Boulder where he teaches organic chemistry to undergraduate and graduate students. He received his Ph.D. from Yale University and carried out postdoctoral research at Harvard University. He has received several national awards for his work in synthetic and mechanistic organic chemistry.

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We have been talking about organic functional groups and so far we have seen that alkanes are carbon hydrogen molecules that contain all sigma bonds. Alkenes contain carbon, carbon double bonds. Alkynes contain carbon, carbon triple bonds. Aromatic hydrocarbons contain a benzene nucleolus or a similar structure in them. We have also seen that alcohols are compounds that contain COH. Ethers contain carbon, oxygen, and carbon. Amines contain nitrogen in the molecule.
Now we are going to talk about a function group that is related to alkenes, in terms of the way it looks and that is the CO pi bond functional group. This is called a carbonyl. When you have a carbon go on like this, that is a carbonyl. The carbonyl is a portion of four functional groups that we are going to talk about. The carbonyls contain analdahides, T-tones, carbosylic acids and esters.
Now, what differentiates these functional groups, is what is attached to the carbonyl. In the case of analdahide, at least one H is attached to the carbonyl. In this case we have a carbon on one side and H on the other. Keytones contain two carbons attached to the carbonyl. These always have at least two carbons. Carbosilic acids contain a carbonyl with an OH bound to the carbonyl on one side and a carbon on the other. Esters contain a carbon here. Instead of the OH, it is an OC bond, and a carbon on the other side. These are the four very important functional groups, not just in organic chemistry, but also in biochemistry.
Now the nomenclature of these is similar to what we have seen before from the other compounds. Aldahides are named with the Greek prefix, in this case meth and the suffix al. So this compound is methanal. The common name for it is formaldehyde. In fact, organic chemists rarely call it methanal, they generally call it formaldehyde. So, I am going to give you both systematic name, as well as the common names. If you hear either of these names, you will be able to recognize the molecules. This compound is commonly called acetaldehyde, but the systematic name is ethanal, because it has two carbons and eth is the Greek prefix for two, el is the suffix for aldahyde. Ethenel is the name of this molecule. Propynel is the next molecule. It contains three carbons. Prop is the Greek prefix for three. Propyneldahid is the common name. Butenel is the name for this molecule, it contains four carbons. Bute is the Greek prefix for four and butenel is the systematic name, with butealdahide being the common name.
Keytones are similarly named. Again you have the Greek prefix for the number of carbons in the molecule. In this case three, prop and ketyone ends in oun, propoun. This is compound is commonly referred to as acetone. And it is the active ingredient in finger nail polish remover. So if I look at this acetone contain product, the contents are acetone, water, proplyn carbonate, blah, blah, blah, so on and so on. But the main ingratiate really is acetone. Butanoun is another keytone. It contains four carbons. The common name for this molecule is methylethylkeytone and is often times abbreviated as MEK, but butanoun is its systematic name. Now when we get to pentagon, we have to worry about the position of the carbonyl. The C double bond O can either be in the two position or the three position. I have drawn here in the three position so that is three pentanoun. And the number three indicates where the carbonyl is, where the C double bond O is. This is also called diethylkeytone, because with have an ethyl group on the right and on the left. This is three hexanon. Again the carbonyl is at the three position. Carbon one, two, three. It would not be correct to call this four hexanoun. Whenever you name these molecules, just like in the case of the functional groups, you give the functional group the lowest number possible in the function group. So, if I called it four hexanoun, that is a higher number and that would not be the systematic nomenclature. So this would also be called propoethylkeytone or ethylpropylkeytone as a common name.
[Carbosilic] acid are similarly named. This is formic acid, methanoic acid. This would be ethylic acid, it contains two carbons. Eth is the Greek prefix for two. Ethynoic acid is this compound. This is also acidic acid and acidic acid is the ingredient in vinegar. When you make your eastern, North Carolina Bar-B-Que sauce, you use vinegar, other Bar-B-Que sauces, as well, and that is the active ingredient. But there is not much in there, it is mostly water. Proponic acid is a three carbon, carbosilic acid and proponic acid is the common name. Butonoic acid is a four carbon, [carbosilic] acid and butyric acid is the common name for that one.
Now esters are generally named by their common names. They are not often named by their systematic names and so I am just going to give you some common names for some esters. Here is ethylactate. It has an ethyl group on the right and the acetate portion is a two-carbon carbosolic portion over ever. That is ethylacetate. And ethyl acetate, if you go and by some non-acetone nail polish remover, the ingredient in that is ethylacetate. The contents in this case are ethylacetate, alcohol. Notice they don't tell you what kind of alcohol is it, but it is probably ethanol, water, propylene carbonate and so on and so on. I like this a lot better, it doesn't dry out my nail. Methylproponate is another ester. Again, the ethyl group is on the left and propionate on the right. Propynate is a three carbon, [carbosilic] containing proportion and that is the common name for that molecule and so on.
Now aldahides and keytones are commonly prepared the oxidation of alcohols. We have talked about what oxidation means in the context of inorganic molecules. But for organic molecules, oxidation is much simpler. Oxidation is the loss of H[2] or the addition of O to an organic molecule. Reduction is the opposite of oxidation, so it is the addition of H[2] or the loss of O to an organic molecule. So if you have a molecule that undergoes a reaction, and the reaction you lose H[2] that is an oxidation.
Here is ethanol. It is a primary alcohol. It has a CH[2] and an OH on it. Remember what a primary alcohol is? A primary alcohol is a molecule that has a CH[2] and on the CH[2] carbon is an OH. That is ethanol. If we oxidize ethanol we generate acid aldahide. So, what we are doing is, we are removing these two hydrogens with our oxidant. We are going to treat this with some oxidant and we are going to lose H[2]. That is what that means, minus H[2]. H[2] is liberated in this reaction. And here is a source of H[2]. These two hydrogens are lost and when they are lost, we form a CO pi bond between the carbon and the oxygen. Now what is left behind is that H right there and that H is that H over there. That is why a primary alcohol can give you an aldahide, because the carbon has two H's and a CH[3] attached to it, in the general case. When we pull off this H, that H is left behind and therefore we are going to generate an aldahide. Because an aldahide has a carbon on one side and an H on the other. If we oxidize a secondary alcohol, we have carbons on both sides and one hydrogen. Again, these two H's are going to be lost in the oxidation process. Because the oxyns are going to pull off these two H's in the reaction by some mechanism and the product is going to be a keytone because what is left behind is the two carbons, not a carbon and a hydrogen, but two carbons.
A common oxyn that is used for these two kinds of reactions, is a chromium[6] agent. Either chromium oxide, or in this case chromate or chromic acid.
Carbosilic acids are mild acids. When a molecule behaves as an acid and donates a proton. Here is methanol. Methanol can donate a proton to give you the H plus, which is a proton and CH[3]L minus. In the case of methanol, the minus charge is stuck on this oxygen. It can't go anywhere, so it is not a very stable species and this is not a very strong acid as a consequence. With acidic acid, when we pull off the proton, here is a proton, we generate this O minus over here. It turns out that this minus charge can be shared between these two oxygens by a process called resonance. We have talked about resonance before, but let me remind you what resonance is. Resonance is the rearrangement of electrons in a molecule, while keeping the atoms in the same position. So, if you have a molecule where you can arrange the electrons in two different ways, the two different arrangements of the electrons are called resonance structures. In this case we have kept all the atoms in the same position, oxygen, carbon, oxygen. We have taken the pair of electrons on this oxygen and formed a pi bond over here. I have indicated that by pushing the electrons over here and then we have broken this CL pi bond. When we have taken this pair of electrons and put on that oxygen, I have indicated that with the arrow right there, to where the electrons go up to the oxygen. So now we have the minus charge up here because now this oxygen has three pairs of electrons on it and this oxygen has a CO double bond. It still has its two electrons from before. So, in so doing, we have shared the minus charge between these two oxygens and we can delocalize the minus charge of a larger area, it becomes more stable. So carbosilic acids are stronger acids because the aniu form is stabilized by resonance.
Well consequence of this stronger acidity is carbosilic acids is increased propensity for hydrogen bonding. So, a carbosilic acid can hydrogen bond. Again, I will refresh your memory of what hydrogen bonding is. Hydrogen bonding requires that we have two things in a molecule. A weakly acidic proton and weakly basic side on the molecule. In the case of carbosilic acids, this is the acidic portion and this is the basic portion. The lone pair on the can act as the mild base and can interact with the proton on the carbosilic acid.
Now, recall when you have a hydrogen bond, you don't fully transfer the proton. All we have is a weak interaction here that provides some stabilization for the molecule to hold when the molecules are close together.
So, because this is a better acid, it is a stronger hydrogen bond donor. This proton is a better donor and that lone pair can form interaction more easily than it can with an alcohol, because it is a better acid.
The consequence of this is that carbosilic acids tend to have higher boiling points that the corresponding molecular alcohols. Here is acidic acid. Overall molecularly this molecule and this propynol are about the same, but the boiling point of acidic acid is 118 degrees and the boiling point of propynol is only 97 degrees. This 21-degree difference in the boiling point, is due to the increased hydrogen bond propensity for acidic acid.
Esters are commonly made from carbosilic acids plus alcohols. If we take a carbosilic acid and an alcohol and treat that with an acid catalyst, a strong acid catalyst we can generate an ester and spit out water. The water comes this OH and that H and I have circled the H and the OH and labeled them in red, so you can't miss it. So these two combine to give off the water and this oxygen and that carbon form the bond of ester. Now this is called a condensation reaction because water is liberated. Water condenses in the reaction and it is liberated. Any time water is produced in a reaction it is called a condensation reaction. And we will see condensation reactions when we talk about polymerizations. Now many polymerization are made by condensation reactions.
Finally I want to summarize all the functional groups we have seen so far and I have known this since I was a child about these functional groups, because when I was a young lad, we used to sing this song. That this guy, Old McDonald, had this farm [ein, ine, ein ine one]. In any case the functional groups that we have seen so far are alkanes. Alkanes is an unfuctionalized hydrocarbons. Alkenes contain the carbon, carbon pi bond. Alkynes are carbon, carbon triple bonds Keytones, here is a keytone, and there is a keytone. Aldahides contain and H, that is the carbonyl. Carbosilic acids are not on this slide, but carbosilic acids is another functional group that we have seen. They look like this. They contain an C double bond O and an OH. Esters contain C double bond O and O and another carbon over here. Amines containe nitrogen.
So, I think the point of breaking organic chemistry into functional groups, is that it makes it easier to understand the structure and the reactivity of the various molecules that you see. If you were to look at a molecule like this and try to understand its reactivity or anything about its structure and you had to look at each of these units as individual little units that would be a pretty daunting process. But if you understand how the various functional groups behave, how they look and how they react, that simplifies a problem from one that is very complex to one that is really quite manageable when you know what the basic reactivity of all these groups are.
Organic Chemistry
The Functional Groups
Carbonyl - Containing Functional Groups Page [3 of 3]

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