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So when we name organicmolecules, the core of what we think about is just how manycarbons form the chain or form the ring that we'relooking at? So let's say I have somethinglike this. And hopefully, you're reasonablyfamiliar with what this represents. And I'll review ita little bit. So let's say I have somethinglike this. Let's say that thatis the molecular structure right there. And so the first question youshould be asking is how many carbons are there? And some of you mightsay, wait, how is that even a molecule? And just as a review, theend point of every line represents a carbon. So that's a carbon, that's acarbon, that's a carbon, that's a carbon, that's acarbon, that's a carbon. And we have one, two, three,four, five, six carbons and we have no double bonds. So if you have all of thatinformation you're ready to name this molecule. And before I actually name it,let me just kind of give you all of the different prefixes. So if you have one carbon,the prefix is meth-. If you have two carbons,the prefix is eth-. And it's good to memorizeat least up to about 10. And actually it kind ofrepeats after that. If you have three carbons,the prefix is prop-. Prop- like propane, and you'veheard of ethane and methane. So you'll see allof that soon. Four, you're talkingabout but-. Five, and after five it kindof becomes the traditional prefixes that we associate witha lot of these numbers. So at five, it's pent-,like pentagon. Six, it's hex- like hexagon. Seven is hept-. Eight is oct-, like octagon. Nine is non-. Ten is dec-. And then after that it kind ofstarts to have a pattern here, and you're not going to reallydeal with things much beyond the teens, but I'll just writethem down here just out of interest. Eleven is undec-. And for those of you who knowFrench, I'm not one of them, but I know that one in Frenchis une, or in Spanish, uno. So it's 1 and 10, 11. Twelve is dodec-. Do or dos, if you're speakingSpanish, for 2. Dec for 10, 2 and10, that's 12. Thirteen, you could imaginewhat it's going to be. It is tridec-. Fourteen is tetradec-. A tetrapod is somethingwith four legs. And after that it, becomesvery systematic. At fifteen is pentadec-. Notice pent-, 5 and 10. Sixteen is hexadec-. Seventeen is heptadec-. So it just goes onand on and on. I don't think I've got to go--anyway, it's hexadec-, heptadec-, octodec- iseighteen, nineteen is nonadec-, and then twentyis actually iso-. But we won't evengo into that. This'll probably serveour purposes. I mean, I could go up tosixteen is hexadec-. So this is just howmany carbons are in our longest chain. What I drew here isjust one chain. So we could immediately--let's try to name it. Well, how many carbonsdo we have here? Well, we have one, two, three,four, five, six carbons. So we'll be dealing withhex- as a prefix. And then to get, I guess, thepost-fix on this prefix, or the kind of the root, you lookto see if there are any double bonds here. And there are no doublebonds here. And if we have no double bondsin this carbon chain, we're dealing with an alkane. This is called an alkane, whichis a general term for all of the chains of carbonsthat have no double bonds on them, or no triple bonds,all single bonds. So in this situation, you takehex- for six, so this is hex-. And then, because it'san alkane, it gets the -ane from alkane. So this is hex-,this is hexane. Let's do another one. Let's say I have thisthing right here. I'll draw-- let's makeit even longer. So let's say I have thatthing right there. So how many carbonsdo we have? We have one, two, three, four,five, six, seven carbons. They're all single bonds,so it's an alkane. So this will be seven carbons. It is heptane because wehave all single bonds. Now, if things form a chain,or if things form a ring, I should say, we put the prefixcyclo- in front of it. So if I have-- let me show youwhat I'm talking about. So if I just have five carbons,one, two, three, four, so one, two, three,four, five. OK, so that's fiveright there. I have one, two, three, four,five carbons in a chain. If I just have five carbons ina chain like this, this would be pentane. But if I have five carbonsand they form a ring, so let me draw it. So it's one, two, three,four, five carbons and it forms a ring. Let me make the drawinga little bit better. So it's really, I'm justdrawing a pentagon. But notice, this hasfive carbons on it. I can draw the carbons here. Carbon, carbon, carbon,carbon, carbon. And just as a review, what youdon't see is the hydrogens they're bonded to. Each of these guys have twobonds, so they must have two bonds with something else andthose are going to be with hydrogen, And I'lll draw it here just asa bit of a review, but you notice very quickly, the drawinggets extremely messy when you draw thetwo hydrogens on each of these carbons. So it's a little bitover-- maybe I shouldn't be doing that. But there you go. So it becomes very messy whenyou draw the hydrogens, so it's better to just assumethat they're there. If we don't draw all four bondsof the carbon, the other two bonds are going tobe with hydrogen. So here, you might say, OK, thisis an alkane, because I don't have any doublebonds here. All of these are singlebonds with the carbon. I have five carbons, so youmight say this is pentane, but you have to think aboutone more thing. It's in a ring, so we addthe prefix cyclo- to it. So this is, because it's a ring,we write cyclopentane. So let me just breakthat apart. This tells us that we'redealing with a ring. You see that this isa ring right there. This tells us that we're dealingwith five carbons, and then this tells us right here,the -ane part, that tells us that they are allsingle bonds. All carbon-carbonsingle bonds. No double or triple bonds. All single bonds. So let's go the other way. Let's start with the word andlet's see if we can figure out what the actual structurewould look like. Let's say I have cyclononane. So what is this telling me? This tells me I'm dealingwith a ring. That is a ring. It's going to havea ring structure. It's going to have nine carbons,nine C's, and then it's an alkane, so they're allgoing to be single bonds. So if I want to draw it, I wantto draw nine carbons in a ring, it's not a trivialthing to draw. I'll try my best, so let's see,that's one, two, three, four, five, six, seven, eight. Let's see, let me draw it. I'll try a little abetter shot at it. So, let's see, you have one,two, three, four, five, six, seven, eight, and then nine. And then you can connect thelast. So let me make sure that this is-- and obviously, I couldhave drawn it better than that, but hopefully, youcan see all of the edges here. So I have one, two, three, four,five, six, seven, eight, nine carbons. It's in a cycle. It's in a ring. I have nine carbons. They're all single bonded, sothis is cyclononane, although there's probably better ways todraw that ring right there. So if someone were to tell you,octane, and that word might feel familiar to youfrom the gas station. They are literally talking aboutthe molecule octane. And now you know, or at leastyou have a sense of what they're talking about. The oct- tells you that youhave eight carbons. There's no cyclo- in front ofit, so it's not a cyclo. It's just going to be a chain. And then the -ane part tellsyou that they're all single bonds, so it's just going to beeight carbons in a chain. One, two, three, four, five,six, seven, eight. It's just going tolook like that. One, two, three, four, five,six, seven, eight. In the next few videos, we'lladd more to these molecules and make the names evenmore complex.