Learn about Organic Chemistry 5, in this comprehensive video by bannanaiscool.
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Rob Lederer: Alkenes are now those aliphatic will stretch in molecules that actually have a double bond, so they all in an ene all the prefixes are the same so now here is how we do? We look at the formula here and as a formula C2H4 right and it follows that general formula right there CnH2n reduce loss two hydrogen's and we have made a double bond. Now, because we don't have as maximum amount of hydrogen on this possible first for a two carbon molecule, which would be 6 carbons but we have 4 carbons instead now they are saturated with hydrogen's anymore that's called an unsaturated molecule, so double and triple bonding chemicals are called unsaturated this is an unsaturated hydro carbon, where as all the alkenes because they are mixed out with hydrogen's are going to be called saturated right. So and it has a lot of implications like polyunsaturated fats and things like that so if you got an unsaturated fat you have a double bond location in that fat that's actually benefit for you, you can break that down easier I will tell you about that later even though this is a kind of a stronger mole. Now that is going to be because there is two carbons and a double bond we are going to call that eth and then of course they are going to end in ene, so that's ethene great, what's this one going to be here well its got the called double bond here and its got three carbons line so that's going to be a propene, sure I mean that's simple, now what about this one yes can get that I know that's butane. Hey! it is but do you realize that you could actually have a double bond here or here which would be a double bond after the first carbon in the chain but this is a double bond after the second carbon in the chain its in between second and third carbon, here what we are going to call it after the second lowest number possible that then what you call it now use an easy a name for it now our u pack is gone to a different type of way of naming. This is the way this the standard way of doing it and it like sound it little awkward to say but this is the way it's done. This is a butane but the ene the double bond is at the second carbon, so here is how you do it's a but-2-ene get it bute for 4 carbons 2 cause the ene is at the 2 ene 2 ene what would the other one be if you actually have the double bond here after the first carbon it would have been butane you don't have to go but-1-ene because if its after the first carbon you always every body and if you just set worked on butane and somebody said to you , draw butane all you have to do is say no that's one, two, three, fours carbons line and then we put that the double after the first one I'm going to take for granted that it is there by the way did you know this how I build back and the temptation might be to put a hydrogen up there can you do that you just go take a mark off because that carbon fill hear four bonds look at all my carbons only have four bonds, so there is one, two, three, four for that one, one, two, three, four for that one and so on right be careful how many bonds you put on. You put one here like that neither five around that carbon, you are going to get the whole thing wrong which is just going to get added to them the little did you get manage you don't want lose to marks be good to the teacher and that will be good to you now look, look this one down here okay this one is going to be you have got a longest continuous chain one, two, three, four, five so that's going to be a pent, where is the ene its after that well its after the third one, no don't always read left to right sometimes its right to left so this one, two after the second carbon from that way we've got the double bond so its going to be an ene at the two so its a pent-2-ene now that's an ethyl group were as an methyl, well when methyl's second one in no, no we already said that the double bond is at the two. So we can start renumbering the longest chain or what its presence, presence like what's more important