Learn about Organic Chemistry 6, in this comprehensive video by bannanaiscool.
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Rob Lederer: Alkynes triple bonds with the general formula CnH2n now we are going to take away basically four Hydrogen's from a saturated molecule we are going to talk about. Today this unsaturated one with the triple bond and so that's going to be CnH2n minus 2 that's general formula, so two carbons along two hydrogen's in either end with the triple bond between. So what's that going to be well two is ethyl of course by the way they are obviously that can't be a methane or methine because it can have a double and triple bond toward nothing. So here is the first in the series of the alkynes and its Ethyne right, so the next one would be or this is the next step after the next one, one, two, three, four that's going to be a bute, but I put the triple bond after the second carbon in order to the first so its but 2 and we've got the Yne after the second carbon so it's but -2 yne right yeah and that's what that is. This is next one the more complicated right this is big okay longest continuous chain of carbons were is it, lets see one, two, three, four, five, six, Seven yeah seven so what's I have to no look at the triple bond than would be in a branch and that's not left longest continuous chain must have the multiple bonding, so therefore this is going to be one, two, three, four, five, six or one, two, three, four, five, six doesn't matter but six is the longest continuous chain because it has to have the multiple bond right, so that's going to be a Hex with the ene at the one so all you have to say is Hexene its okay you want to get Hex one ene that's all right now there is two branches, where are the branches here and here, so if that's the Hexene come on can you get its an yne hexyne you got that. Now there is your longest continuous chain here are you two branches these are ethyl branches right and these ethyl's are attached were, well we started here with the triple bonds and we decided and that's the one and exist the two, so there fore there is an ethyl at the two and ethyl at the four so its two, four how many ethyl's diethylhexeyne one word 2-4-diethylhexyne that's how you do. A tricky one and some shape. Okay here is butyne yeah its, you just have a fun now and what's this all about no you got to know how to do that one there is two double bounds in this molecule, how do you name it. Well, if you said that this would be a dibutyne that wouldn't begin because you don't have two dibuts all right , you have two enes you have two multiple bonds two double bonds so how you are going to name that you are going to say well okay there is two enes that's a diene in a four carbon chain which is a but so this is going to be bute, now because the next word that we have is going to have a consonant in it we instead of a vowel to make it flow its buta right so its buta what well here is a double bond at the one in the three, so it's a get ready it's a buta 1, 3, - 2 enes diene, buta -1, 3 diene . That you should actually be called 1, 3 butadiene it separated the numbers and the letters it flow nicer but this actually explains it better again. Now you are something else that you got to remember about when you start building molecules of things like alkynes, enes and ienes and necessary shapes when we talk about the tetrahedral nature around the carbons for all the alkynes now what's going to happen when you have double bond we are going to have this here is your C2H4 and go back to ethyne this is an ethyne there is a double bond in the middle represents with springs through a now remember what the shape is this has, this carbon atom has one, two, three affective pairs around in there we have three affective pairs around the central atom you got yourself a tri mono planar shape remember that so this tri mono planar around this one and that one too. So there is two tri mono planar here by tri mono planar if you will two tri mono planar but of course if you have triple bond and two carbons you are going to have this type of shape rig