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Functional groups

Various functional groups can be attached to hydrocarbons, effecting chemical properties. Hydroxyl groups are polar, turn molecules into alcohols, and allow molecules to dissolve in water. Carboxyl groups can donate hydrogen ions, so they make molecules acidic. Amino groups can pick up hydrogen ions from the surroundings, so they make molecules basic. Other functional groups include sulfhydryl, carbonyl, methyl, and phosphate groups.

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  • duskpin ultimate style avatar for user Brett Wallner
    Hi, I have a question - sorry if it's stupid but I'm a little confused. I tried re-watching the video and I couldn't really figure it out.
    At Sal says that when Hydroxyl is attached to a carbon backbone it turns the entire molecule into an alcohol.
    Then later in the video he shows the sugar Fructose, and there are tons of Hydroxyl groups on the molecule.
    How is it a sugar and not an alcohol? Is the Carbonyl group somehow "strong" enough to cancel out the alcoholic properties of the molecule? Or perhaps do you need a full chain of only Hydroxyl to make it an alcohol? Or does this only apply to Ethanol?
    Please feel free to go in-depth on this if you know the answer, I always want to learn more and anything would help. Thanks!
    (22 votes)
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    • male robot hal style avatar for user Pranay Gosar
      In that part of the video, Sal shows that fructose has a carbonyl group. He also says that this makes it into a sugar. This means that no matter how many Hydroxyl groups you have on a molecule, if it has a carbonyl group, it can't be an alcohol anymore, instead, it is classified as a sugar.
      Remember, all it takes is one atom for the entire molecule to be radically changed, in this case, the carbonyl group.
      (39 votes)
  • leafers ultimate style avatar for user John Korossav
    At about he says that the methyl group is not polar. Wouldn't it be polar since carbon has greater electronegativity than the hydrogens it is bonded too? The hydrogens should spend less time with their electrons making them partially positive, and therefore able to form hydrogen bonds with H2O. At least thats my understanding of it. Why am I wrong?
    (11 votes)
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    • old spice man green style avatar for user Matt B
      Every atom has different electronegativites, so as long as two different atoms are bonded, they will always be polar to some degree. That said, the difference in electronegativities is far too small in methyl to make any difference, which is why C-H bonds are considered non-polar.
      (17 votes)
  • male robot hal style avatar for user RandomDad
    Why we always named -OH as acidic group since it looks like base molecules because it ends with (-OH) not only (-H). It makes me confused.
    (8 votes)
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    • old spice man green style avatar for user Matt B
      O=C-O-H is the carboxylic group and is strongly acidic because of the resonance that forms between the two oxygen atoms and the carbon. -OH in alcohols is much less acidic, but it too can lose that proton.
      (12 votes)
  • leafers seedling style avatar for user Tanya Medina
    At the video begins to discuss Leucine. Going into the carboxyl group, amino group, and R group. I was trying to name the compound, but am stuck. Can you please give the name? 4-methyl, 2-amino, 1-carboxyl pent-1-ene?
    (6 votes)
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  • male robot donald style avatar for user Aashish Chaudhary
    what is the longest carbon chain found in nature? 100?
    (5 votes)
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    • old spice man green style avatar for user Matt B
      The longest molecules I can think of is DNA, which will have 3 billion base pairs, or 6 billion bases. I don't know the exact numbers but my best estimate would be between 10 and 100 billion.
      Btw, complex carbohydrates can easily be longer than 100 carbon atoms long ;-)
      (8 votes)
  • purple pi pink style avatar for user stuffundefined
    If water has an HO group, does that make it an alcohol?
    (4 votes)
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  • hopper jumping style avatar for user Amir
    At Sal says the nitrogen's lone pair of electrons can form a bond with a hydrogen ion.

    This confuses me: how can nitrogen's two electrons form a bond with hydrogen's one electron?
    (4 votes)
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  • aqualine tree style avatar for user Hafeez
    What does "polar" mean?
    (2 votes)
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  • piceratops ultimate style avatar for user Gabriel
    The video explains, at ,that the Carboxyl group of the Leucine Amino Acid can readily give up the hydrogen proton. The video also explains, at , that the oxygen - which recently gave up the proton - can stabilise with the carbon of that Carboxyl group.

    The video goes on to explain about the Amino group of the Leucine Amino Acid and, at , explains that the Nitrogen atom can pick up a hydrogen ion. Therefore one can conclude that both the Carboxyl group and Amino group can bond with a hydrogen atom.

    I then ask if there is the possibility of an Amino acid with an oxygen atom bonded in the Amino group instead of the Carboxyl group? This question is based upon the fact that the Carboxyl group can readily stabilise without the hydrogen atom.

    I also ask if the Carboxyl group can give up the hydrogen proton - now an ion - to the Amino group? Or is it that the oxygen of the Carboxyl group has a stronger attraction of hydrogen atoms then that of the nitrogen in the Amino group and that the Carboxyl group would only give up the hydrogen to another molecule or atom possessing a greater attraction of it?
    (4 votes)
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    • winston baby style avatar for user Ivana - Science trainee
      If oxygen atom binds to the amino group then it does no longer stay as an amino group and we are not speaking about amino acids.

      Yes, the carboxyl group can give a hydrogen to an amino group. It is called aminotransfer when you create 2 new amino acids between alpha-keto acid and amino acid. I'll illustrate an example of:

      Glutamate + oxaloacetate ↔ α-ketoglutarate + aspartate
      (1 vote)
  • primosaur ultimate style avatar for user nickeldime88
    How are hydrogen atoms amino acids?
    (3 votes)
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Video transcript

- [Voiceover] We spent some time talking about hydrocarbons and hydrocarbons are interesting especially if you want to combust things, if you want some fuel, but now we're going to make things a little bit more interesting by adding things to the hydrocarbons and the things we're gonna add we call functional groups. Functional groups. And my goal in my video is to give you an overview of the major functional groups that you might see attached to carbon backbones that make the molecules interesting biologically. Now, the first one I will focus on is an OH group. So, we have an OH attached to a carbon backbone over here. It doesn't have to be attached to a carbon backbone but the OH right over here, this is called a hydroxyl group. Hy, hydroxyl group, and when it is attached to a carbon backbone like this one is then it turns the entire molecule into an alcohol. Alcohol. This an alcohol. And this one in particular if you want the name we have two carbons on the longest, longest chain and it is an alcohol so we use the prefix Eth for the two carbons. So, let me write that down. We're going to use the prefix Eth because we have two carbons here. And we're gonna say Ethanol. Now, what are the properties here? Well, you have oxygen which is very electronegative bonded to a hydrogen and to a carbon but the oxygen is a lot more electronegative than the hydrogen so you're going to have a partially negative charge at this end away from the hydrogen. A partial positive charge at the hydrogen and to a lesser degree the carbon end too but hydrogen is even less, is a less electronegative than even carbon. And this one, so, a hydroxyl group they are polar, they are polar, and because they are polar you can dissolve them into water. They are hydrophilic. They can form hydrogen bonds so that you can dissolve this. Now, similar, a similar functional group or one that has somewhat similar properties is right over here. And you might say, "Wait, why is this one similar? "I have sulfur here instead of oxygen." But if you look at the periodic table you will see that sulfur and oxygen both have six valence electrons. They both would love nothing more than to grab or pretend to grab two other electrons and this is why they form, they tend to form two covalent bonds. And so, this group right over here, which is called a sulfhydryl group. This is a sulf.... Sulfhydryl. Sulfhydryl group. It's kind of similar to a hydroxyl group with the one difference, with the one difference that sulfur is electronegative but it is less electronegative than oxygen. So, you're still gonna have a partially negative charge and a partially positive charge, but it's going to be less polar. So, it's not quite as polar as if you had a hydroxyl group. Now, when you have this sulfhydryl group it's attached to, say, a carbon chain and when I use this R right over here, when I have this R. This is just shorthand for carbon and a bunch of other stuff. I could've, if I wanted to generalize an alcohol right over here I could've written R and then I could've written the hydroxyl group. O and then bond that, bond that to an H. So, over here the shorthand R would have been the shorthand for all of... The R would've been the shorthand for all of this business. All of this business right over here. And so that's what we're doing over there. I'm not saying that this R is exactly this. It means that some carbon backbone and some carbons, hydrogens, and maybe other stuff, maybe even some other functional groups, but we're just focused on the sulfhydryl right over here. And so if you see something like this, you'd say "Okay, yeah, this is still going to be polar, "but not quite as polar as if I were dealing "with a hydroxyl group." Now over here we have a more complex molecule, but this is a molecule that you run into probably on a daily basis. This is the sugar fructose. This is the sugar fructose. And this is when it is not in a ring. If you were to throw this into-- If you were to throw this into water, it'll readily form a ring, but when it is not in a ring form you can recognize already the hydroxyl groups. You have a hydroxyl group on this carbon. You have a hydroxyl group on this carbon. Hydroxyl group on this carbon. You have a hydroxyl group on that carbon. You have a hydroxyl group on this carbon. And then, on this carbon, it's double bonded to an oxygen. We call this a carbonyl group. So this is a carbonyl. Carbonyl. Carbonyl group. Now this is actually how you would tell a sugar, it's like, look, especially when it's in a straight chain, all my carbons have one hydroxyl on them except for this one, it has a carbonyl group. And one of the take aways for a carbonyl group, we've already talked about oxygen being very electronegative, even more electronegative than carbon, it's double bonds, it's going to hog the electrons on the oxygen end, so you're going to have a partially negative charge. Partially negative charge over here, partially positive charge over here, and so this, this one is also going to be polar. And then, in fact, the entire molecule is very polar because it has all these hydroxyl groups on it as well, but this is also going to give it polarity here and, because this carbon has a slightly positive charge, it is susceptible to nucleophilic attack, and when you take organic chemistry, you'll see that things that want to share-- That have a predisposition to share their electrons in a bond might want to come and form a bond with this carbon and maybe one of these electron pairs go back to this oxygen and maybe bond with something else, but we'll talk about it in the future when we study some organic chemistry mechanisms. The important thing here is just recognize, "Okay, I've got some hydroxyl groups? "Okay, I've got a carbonyl group right over here as well." Now this molecule, this is an amino acid, and you will see amino acids a lot when you study biology. And this has actually a couple of interesting groups on it. The first group of note is this stuff that I am circling in orange because you have a carbon that, you could say it's part of a carbonyl group, but it is also bound to a hydroxyl group. It is also bound to a hydroxyl group right over there. And when you have this configuration where you have a carbon bond double-bonded to an oxygen and then single-bonded to a hydroxyl group, we call this a carboxyl group. This is a carboxyl. Carboxyl, carboxyl group. And one of the take aways from this is that it is acidic because this can readily give up the hydrogen proton. This oxygen, we already know oxygen likes to hog electrons, it can take up both of these electrons and become negative, and actually, there's actually resonance here because those electrons get shared throughout the group and actually even potentially even beyond the group but especially inside of the group, then leaving the hydrogen proton. So this can readily donate a hydrogen proton... This can readily donate a hydrogen proton, so this is generally viewed as acidic. Acidic. Now, this amino acid over here, it also, and this is where this name comes from, actually the acid comes from this carboxyl group, this is the acidic part, and then you have an animo group. You have an amino group right, right over here. And because it's involving a nitrogen, this is the amino group. This is what gives the amino part of the name amino acid. Amino acid. And this actually is generally basic. Because nitogen could-- It has a lone pair. It has a lone pair of electrons right over here. And so it could use that lone pair to pick up, to form a bond with a hydrogen ion, to pick up a hydrogen ion. So, under the right circumstances, it can form a bond with a hydrogen ion, which, we know, a positive ion, which would just be a proton, and so it would have a positive charge. And so since it can sop up hydrogen ions, we can view this, the amino group, as being basic. But this right over here is leucine, it's an amino acid super important for muscle growth, but there you can appreciate. You have essentially a hydrocarbon chain, but it has a carboxyl group at this end and an animo group right over here. And another thing that you'll sometimes people talk about is even hydrocarbon groups. For example, if you consider the main chain of this, and we could consider to either using this carbon or this carbon, but if we consider this to be the main chain of carbons, if we consider that to be the main chain of carbons, then we would consider this right over here to be a methyl group. Remember, the prefix "meth" refers to one carbon, so it's one carbon bonded to a bunch of hydrogens, to three hydrogens here, and so we would call this a methyl group. And in general, if you have a hydrocarbon bonded to other hydrocarbon groups, these things are hydrophobic. So these things, there's nothing polar about them, and so they're not going to want to, at least these parts of the molecule are not going to naturally dissolve inside of water. Now the last group we're going to focus on, and you're going to see a lot of these, and especially in biology, you're going to see this as a part of ATP, you're going to see it's the backbone of DNA, and that's phosphate groups. And this right over here, this right over here is the phosphate group. I've drawn it bonded to a bunch of, kind of a group over here, who knows what it is, bunch of carbons, a bunch of other things, and then I've bonded it to two hydrogens, but it doesn't always have to be bound to hydrogens. But when it is bound to hydrogens like this, it's considered to be protonated, and so it can actually take up, it can actually hog these electrons and dump these hydrogens, and dump these hydrogens into a solution. So a phosphate group is considered to be acidic. It is considered as well, especially when it is protonated like this, it is considered to be acidic because it can donate protons. So this is just an overview of a lot of the functional groups you will see throughout biology and a lot of big, hairy complex molecules, when you actually break it down, you say, "Okay, there's a hydrocarbon chain there. "Oh, I see a sugar there! "I see a bunch of hydroxyls, and I have a carbonyl group. "Oh, I see an amine group, I see-- "Or, amino group. "I see a carboxyl group." You can think about this going to be acidic? Is it going to be polar? Or do different parts of the molecule have different functions?