If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Hydrocarbon overview

Hydrocarbon overview.

Want to join the conversation?

  • primosaur ultimate style avatar for user nickeldime88
    At -, does alkane, alkene, and alkine have anything to do with alkaline?
    (20 votes)
    Default Khan Academy avatar avatar for user
  • leafers tree style avatar for user radiohead6395
    does the double bond mean those carbons share two electrons?
    (13 votes)
    Default Khan Academy avatar avatar for user
  • starky ultimate style avatar for user Kelvin A. Barry, Jr.
    can carbon combine with a water molecule?
    (10 votes)
    Default Khan Academy avatar avatar for user
  • orange juice squid orange style avatar for user JAY K.
    For the Enantiomer, what would its chemical formula be, and how do you determine the formula for compounds like these.
    (8 votes)
    Default Khan Academy avatar avatar for user
    • duskpin ultimate style avatar for user Sankalp201516
      Bottom line for today: you can tell if molecules are enantiomers or diastereomers by looking at their (R,S) designations.

      Enantiomers are non-superimposable mirror images of each other. Pardon me while I push the Caps Lock button:


      Buy “opposite” I mean they have the same names, but their R’s and S’s are reversed.

      The enantiomer of (S)-2-chlorobutane? It’s (R)-2-chlorobutane.

      The enantiomer of (R)-2-butanol? It’s (S)-2-butanol.

      Let’s say you’ve got a molecule with two stereocenters and the configuration is (R,R). The enantiomer will be the molecule with the exact same name except it’s (S,S). For instance, the enantiomer of (2R,3R)2-bromo-3-iodobutane is (2S,3S)2-bromo-3-iodobutane.
      If you’ve got a chiral molecule with two stereocenters and the configuration is (R,S), the enantiomer will have the (S,R) configuration.
      Taking it even further, if we had a molecule that was (R,R,S,R)-(followed by long chemical name), what would its enantiomer be? It would be (S,S,R,S). Get the idea?
      (12 votes)
  • piceratops sapling style avatar for user Kevin Tony
    i thought it was called 2-methyl but-2-ene. is this correct as well? because that's how i was taught.
    (6 votes)
    Default Khan Academy avatar avatar for user
    • female robot grace style avatar for user Mary
      I was taught the same way, and I was confused at that. I'm not sure if Sal made a mistake or if it is simply another way of writing it. I would stick to writing it with the double bond location after the number of carbons in the longest chain.
      (2 votes)
  • blobby green style avatar for user Amy Renton
    Does the '2' before the 'butene' in 2-methyl-2-butene' refer to the position of the double bond? Thanks!
    (4 votes)
    Default Khan Academy avatar avatar for user
  • duskpin ultimate style avatar for user mqian36
    What's the difference between a single, double, and triple bond between carbons?
    (2 votes)
    Default Khan Academy avatar avatar for user
  • leaf green style avatar for user harleentaneja16
    What is an alkyl group. What is its general form in which it is written and when is it used? Is an Alkyl group also a functional group or is it part of the Alkanes?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • female robot grace style avatar for user tyersome
      You can think of an alkyl group as being an alkane where one hydrogen is replaced with a bond.

      For example, an ethyl group is H₃C-CH₂- (compare with ethane H₃C-CH₃).

      There is no general form for any alkane since they could contain one or more rings and thus there can be no general form for alkyl groups.

      My understanding is that any group contributing to a molecules properties/reactions is a functional group, so yes alkyl groups are a type of functional group.

      Does that help?
      (4 votes)
  • duskpin ultimate style avatar for user Mary
    at it is mentioned that many molecules in biology have hydrocarbon chains. Else where in the Properties of Carbon videos it is mentioned that hydrocarbons tend to be molecules in fuels. Does a hydrocarbon chain in a biology molecule provide that molecule fuel?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • female robot grace style avatar for user Themidnightsamurai
      hydrocarbons are a structurally diverse group of molecules, including fossil fuels, several kinds of plastic, and paraffin wax. Fossil fuels such as coal, oil, and natural gas burn readily, reacting with oxygen to release energy as the hydrocarbon molecules are broken apart, forming carbon dioxide and water.
      (3 votes)
  • blobby green style avatar for user Hafsa Buriro
    what is quadruple bond, it is mostly being discussed here?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • old spice man green style avatar for user Matt B
      A quadruple bond is a covalent bond (Chemistry) with 4 shared electron pairs, so 8 total electron in one bond. While double bonds are frequent in organic matter and triple bonds are already quite less frequent, quadruple bonds don't really occur because they are too unstable and I am unsure why they are being discussed (other than "for fun")
      (3 votes)

Video transcript

We've already spent a lot of time talking about how neat carbon is for life and for biology and for chemical reactions so much so that there's a whole field of organic chemistry devoted to studying the chemistry of molecules that involve carbon and one of the things that carbon - or two of the things that carbon will often bond with are itself and with hydrogens so much so that there's an entire class of molecules that are only made up of carbons and hydrogens and we call these it's a very creative name we call them hydrocarbons - hydrocarbons and you will see many many types of pure hydrocarbons and you'll see many other types of molecules that at least are partially hydrocarbons or are based on hydrocarbons so it's a really interesting thing to study here's three examples of hydrocarbons these all have the prefix eth- in the beginning of them because they have a chain their longest chain has two carbons and if you want to study how to name hydrocarbons or actually organic compounds in general I encourage you to look at the organic chemistry section of Khan Academy where we go into depth on it but this is just going to get you just kind of dip our toe in the water just so we get a little bit familiar so these all have the prefix eth- which says our longest chain of carbon we're gonna have two carbons over here but then we see that the ending is different over here we have ethane and it's it's an ane because we have a single bond over here this over here we have an ene and that's because we have a double bond we have at least one double bond in that chain that and the carbon chain is only two carbons over here and it's ethyne here because we have a triple bond the general term for a carbon chain that has no double or triple bonds is an alkane this is a specific form of an alkane ethane that has two carbons if the general form for carbons that have a double bond that's an alkene actually let me write these general terms down so I could write al alkane alkane is the general term for a chain of carbons that has no double or triple bonds and specifically this is ethane if I were generally here and say alkene now it's alkine right over here let's think a little bit about how this bond effects effects its shape well here I have a single bond so it essentially forms two tetrahedrons with one of the carbons at each of the centers of those tetrahedrons for example on the left hand side here when I when I draw this bond popping when I draw it like this it means that it's popping out and when I draw it like this with these lies that means it's going into into the screen so I could draw a tetrahedron that looks that looks like this that's the base of it and then the top of it is that this other carbon and it has it has this carbon at the center and I could also draw another tetrahedron that has this carbon at the center this carbon at its top and it would look it would look something it would look something like it would look something like this so for at least for this molecule you have the shape is kind of it looks like these two tetrahedrons that are kind of overlapping with each other and because these carbons are they have a single bond in between them they these two tetrahedrons can rotate so they could rotate they could rotate around they could rotate around that single bond now things are a little bit different when you have a double bond when you have a double bond like this it actually forces all of these all of these atoms in this molecule to be in the same plane so this right over here this ethane this is planar this is planar right over here and these this double bond locks it into place there's not going to be any rotation when you have a triple bond not only are you not going to have any rotation but it's gonna make the whole thing it's going to make the whole thing a linear molecule so when we're talking about its shape we're talking about these molecules their conformation how do they arrange themselves in three dimensions and if you're curious what these are ethane is a component of natural gas most of natural gas is methane methane is just so if I were to write methane most of natural gas is methane which is just one which is just one carbon bonded to four hydrogens that's methane right over here this is most of this is the biggest constituent of natural gas but you're going to find a little bit of ethane in there ethene which is often known as ethylene this has many industrial uses but maybe most interestingly it can be used as a plant hormone that can be used to ripen fruit ethyne a lot most commonly known as acetylene this can be used because it burns very very hot it can be used to fuel blowtorches so once again you know these are they seem similar but there can be used for very very different things and I could go all day showing more and more different types of hydrocarbons but here's just a little bit more variety just so we can think about how they're named and the different forms they take and these are just three of the different types of molecules you might find in the gasoline that you have in your car and there's many many more than just these and that's because you mix them with oxygen put them in an engine and and and spite and spark them right that they burn well there they're good fuels to to power cars but just so get familiar with the naming mechanism a little bit more this is pentane it's an alkane with five carbons one two three four five carbons in its longer longest chain that's why it's called pentane because hydrogens are all of the other bonds that a carbons are forming sometimes you'll see a shorthand where something like a pentane instead of drawing all the Cs and Hs it would be drawn like this it could be drawn like this where you assume that there's just a carbon at each of these points over there so you actually don't have to draw the carbon and then if you don't see if you don't if something's not bonded to a carbon it there's no other atom that is drawn in that the carbon is bonded to you assume it's just a bunch of hydrogen so this is a shorthand for pentane which is exactly this molecule here and you see it has this kind of it has this bend shape because carbon is each of the carbons are trying to get to that tetrahedral type of shape now this this is cyclohexane once again it's an alkane we have no double bonds here hex- is the prefix because you have six carbons in your longest chain one two three or you could say your cycle in this case 5 6 and the cyclo is because instead of it just being a instead of it being an open instead of it just being an open chain it's connected at the end it forms it forms actual cycle this over here looks a little more complex you see the -ene at the end and that's because the longest chain has a double bond right over here and the but- this is the prefix for four this means that our longest chain has four carbons and you see that one two three four carbons but then on this number two carbon not only did you have your double bond there but you also have a methyl group a methyl group 1 carbon meth- is the meth is the prefix meth- is the prefix for one so anyway the goal of this video is really just to give you a little bit familiar with with hydrocarbons and and to think about how they'll be useful in chemistry and parts of and and and you'll see many molecules in biology that have hydrocarbon parts that have chains of hydrocarbons attached to them so we can think about the properties associated with them.