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Current time:0:00Total duration:7:34

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 hydrogen's so much so that there's an entire class of molecules that are only made up of carbons and hydrogen's 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 our 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 F 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 F which says our longest chain of carbon we're going to 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 N because we have a single bond over here this over here we have an N 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 fine 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 four 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 to speak generally here and say alkyne now it's alkine right over here let's think a little bit about how this bond effects affect its shape well here I have a single bond so it essentially forms two tetrahedrons with one of the carbons at each of the centres 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 lines 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 carbonate is 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 hydrogen's that's methane right over here this is most of this is the biggest constituent of na gasps 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 f-fine Oh 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 Speight 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 hydrogen's are all of the other bonds that the carbons are forming sometimes you'll see a shorthand where something like a pentane instead of drawing all the Seas and H's 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 bent shape because carbon is each of the carbons they're 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 1 2 3 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 een at the end and that's because the longest chain has a double bond right over here and the Butte this is the prefix for for 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 one 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
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