hello organic chemistry students in this video we're going to cover the introduction of alkenes which includes its nomenclature and then start talking about a very important intermediate in chemical reactions called carbocations now what I've shown right here are four alken molecules they all they're all alkenes because there's a carbon carbon double bond present in them so each one of them is an alen now the question I'd like to ask really quickly is is this molecule an alen and the answer is no because there's not a carbon carbon double bond there's a carbon oxygen double bond here and this is the aldhy functional group but it is not an alen so not an alken It's actually an alcane because all the carbon carbon bonds are singly bound to one another now let's go ahead and just jump right into the nomenclature of alken so I'm just going to draw this four carbon long molecule that we saw up above the rules are going to be pretty much the same that we saw with the alkanes with one small exception we're going to find the longest carbon chain that contains the double bond or double bonds we can have multiple here luckily we just have one carbon chain there's a grand total of four carbons in it so our prefix nomenclature Remains the Same this is butes for 1 2 3 4 but now we have a double bond so we can't say a n e we're actually going to say e ne e buttin but now if I was to give you this molecule right here wouldn't it also be called buttine it sure would and then what about this molecule right here that is also four carbons long with a double bond in it that's a problem we can't have four or three compounds with the same exact name the one thing that's different here is where the double bond is located now when we're naming molecules with double bonds we have to give that double bond the lowest possible numbering so when we look at the top one we're going to go one 2 3 4 we always start with the number that numbers through the double bond so this is called one buttine down below it's called two buttine and the third one is two buttine as well well nuts we're able to figure out how to um specify the first one nicely but now we have two of the same names down below oh no so now if we imagine that we draw a plane through the double bond in each one of these cases in the top one the methyl groups on each side of the double bond are on opposite sides of the double bond down below from this plane they're both on the same side and that's going to be our key difference this one is called a trans double bond because the groups are on opposite sides and the bottom one is called a CIS double bond because they're on the same side CIS for same ah that kind of sounds nice now this is the basics of the nomenclature system let's go ahead and practice it a little bit more all right going to give a nice long carbon chain and this time I'm going to put two double Bonds in now the rules stay the same actually we'll go ahead and put some sub some substituents on this system as well so now we're going to find the longest carbon chain that contains the double bonds which is this one right here in red and when we look at this we have 1 2 3 4 five six seven carbons in total so we're looking at the name Heep now there's two double Bonds in it so we are going to use e ne e but now if you notice I'm leaving a big gap right here for a reason how many double bonds are present in this molecule there's two of them so we're going to go back to our nomenclature prefixes and use D we have a dying here now this is is called Hep dine but that sounds a little weird so what we do is we put an a at the end heptad dine that a is not implying that there's an alkane by any means no no no no it's not all it's doing is making it sound a little nicer a little nicer heptad if there were six carbons it would be hexad and so forth and so on now just like we did up above we have to number where those double bonds are and we have to give it the lowest possible numbering so 1 2 3 4 5 6 7 if I did it in the other way this would be 1 2 3 4 5 6 and 7 keeping in mind that we have to number the double bonds with the lowest numbering the red nomenclature is the best so we're going to call this five heptad now we can write it another way where we can put the hepta and then put the 15 that Dash dying behind it so you can do it either way and it's perfectly correct when we have these double or two double bonds or three double bonds now we have substituents on this ring we have methyl groups up above right here and we have an ethyl group down below now right now you might be saying but wait wait wait what about cysts and trans this double bond right here doesn't have two substituents on it it only has one so in order to say CIS and trans we need two substituents on that double bond so here because we only have one there's no cyst trans nomenclature here one substituent's pointing down this one's pointing up so that double bond is a trans double bond and we're going to get into the naming of that at the very end of this molecule let's go ahead and write down our substituents in alphabetical order we have ethyl and then we have dimethyl HEPA 15 diione it's the same name up above as well I'm just writing W it down below the ethyl group is on carbon oops not carbon 5 on carbon 3 with the red numbering and the methyl groups are on carbon 44 dimethyl so here we have three ethyl 44 dimethyl hepto one5 dying we're almost done what do we need at the beginning we're going to write the name trans now you can have it in parentheses or you can just leave it without parentheses for this class we are not going to use parentheses this is the most correct way of doing it nowadays we are slowly switching the nomenclature to say no parentheses around it but you will still still see some examples of it where there's a a parenthesis but we are not using parentheses in this class and we put that right at the front of the molecule this trans indicates where this five's double bond is the one is at the terminal end so there's no CIS or trans the three indicates where the ethyl is the 44 indicate where the methyls are and the five right here indicate where the ding is and that is our nomenclature of alkenes the rest of the nomenclature rules are exactly the same as we saw with alkanes if we put a chlorine in a Florine a bromine a Nitro or cyano group we would use all the same prefixes as substituents and put it onto this molecule just like we saw previously but the one that I really like to talk about right now are what if it was a ring as shown there are six carbons in here so we have a cyclo hexene now that is the official name for it cyclohexene but if you put in one cyclohexene that would also be correct we don't have to say one because the carbon with the double bond has to be carbon one in this ring now you might also be thinking we have to say Cy one cyclohexene we don't for seven carbons for rings that contain seven seven carbons and Below all they can ever be is Cy in confirmation we are never going to see greater than that in this class so we're only looking at the Cy type of cyc alkanes or alkenes excuse me and therefore we don't have to indicate CIS or Trans in front of it let's go ahead and practice one let's name this molecule right here I went ahead and made a cyclopentene just to switch it up a little bit now the double bond has to be number one so we know it's one cycop penene oops and there's an e at the end so here's carbon one here's Carbon 2 and three or wait a second could I have gone 1 2 3 4 5 no matter which numbering system I use the double bond is given the lowest numbering so that's fine so we have to look at the substituent as well the red numbering puts the two methyl groups on five where the white numbering puts it on three so therefore we're going to use the white numbering here and go 33 dimethyl one cyop pentin and that is the nomenclature behind alenes pretty nice now if we just have two substituents on the double bond the CIS and trans nomenclature works perfectly but if you have three or four substituents we have to change it up ever so slightly and let's go ahead and get into that so what if we have Tri or Tetra substituted olins wait what on Earth is an olant oops let me put the E right there let's just make this correctly spelled Olan right here an Olan is basically just a double bond it's another word for it so whenever you hear the word Olan it means a carbon carbon double bond so if I go ahead and write this molecule right here and I'm going to put a chlorine right there how many substituents are on this double bond first of all a substit stituent is anything but hydrogen I know hydrogen gets the short end of the stick yet again so anything but hydrogen so we have a methyl group here a hydrogen which we don't care about so here's one chlorine for two ethyl group for three that's a tri substituted all them what we now need to do is take both carbons of the Ring system and we have to rank them so this carbon here and oops can't really see that this carbon here and this carbon here and we we have to rank priority groups so to do this the first thing I'm going to do is chop this double bond right in half we're going to look at the left side and the right side independently on the left side we have a hydrogen and a carbon so I'm going to draw those hydrogens in now how are we going to how are we going to determine what's high priority versus low priority atomic numbers we're going to look at the groups directly attached to the double bond we have a hydrogen and a carbon which which one has a higher atomic number that's right carbon so this is our top priority group this is our second priority group you could write H or L whatever you would like let's look at the other side on the other side we have a chlorine versus carbon which one has a higher atomic number absolutely right chlorine versus carbon now you might be saying wait there's more carbons over here and hydrogens doesn't matter we're going to look at each attachment until we find a different difference in atomic numbering and we're going to do another example of that here in a couple of moments so now here both the high priority groups are on the same side of the double bond which we would normally call a Cy double bond what do we call it here a z double bond which means the two priority groups are on the same side so this has a z geometry let's go ahead and name this molecule so when we're numbering this we have to give the carbon carbon double bond the lowest possible numbering we have five carbons in here so we're looking at Pence we're going to put the double bond on Carbon 2 for the lowest numbering and then we have a chlorine on carbon 3 so we have three chloro 2 penene we now have to indicate Z in front the Z in front tells us that the two highest priority groups on that double bond are on the same side and that's the nomenclature behind e and z I should say Z and we don't know e yet now what if if I go ahead and draw this line right here what if I gave you this molecule where I switched the chlorine and the ethyl group this is still the high priority high priority those are now on opposite sides of the double bond and that would be given the E confirmation for this molecule so e looks just like trans Z looks just like Cy or the same now we put that right at the front of the naming system right here just like we did with CIS and trans and beyond that it's all identical so once again to recap we use Cy and trans if we have a disubstituted Olan meaning there's a substituent on each carbon of the double bond you can't have two on the same carbon you have to have one substituent on each carbon of the double bond for tri and Tetra we have to have three or four substituents on the carbon carbon double bond system all right that is the introduction into nomenclature of these molecules the last thing that I'd like to cover in this video is a very important concept called carotin now before I even talk about what a carbocation is I want to use a non-chemistry illustration I want you to imagine it's the end of the semester and you're moving out of your house apartment wherever you might live you have to pack up all your stuff be even beyond that packing up all your stuff is not fun but let's say you have it all packed up so you're sitting there you have boxes everywhere and a moving truck outside if it's just you moving all this how fun is that it's not very fun at all it's a lot of hard work for you isn't it absolutely it is what if one friend shows up if just one friend comes and shows up at your apartment or house and helps you move you get done 50% quicker so that one friend is helping to carry the load of your possessions what if two friends show up wow that's three people moving things that's even easier right what if four friends show up that's even better oh my gosh so if two friends or three friends or four friends show up the more friends that are there the easier the job is right but now let's say you have two friends with you so there's three of you there and then one of your best friends in the world calls you on the telephone is that friend on the telephone helping you at all move your stuff no they have to be directly there to help you move your stuff so the more friends that you have directly there with you the easier the job it is to move your stuff how on Earth does this relate to chemistry let's get into it so now a carbocation is defined as a carbon with an open p orbital and three other bonds so as a whole here's the carbon and here is the three other bonds connected to something we'll go ahead and just say r or Z whatever you would like it can be anything actually know for here for carbocations we're going to keep it as carbons or hydrogen so we get rid of those Z's and that carbon has a full out positive charge if I rotate this so it's coming out of the plane here's the carbon here's one R group right here one going into the plane another one coming out of the plane so as a whole R1 is part of the plane that we're looking at R2 is going into it R3 is coming out of it here is that open p orbital completely devoid of electrons and that carbon is therefore missing one electron and a positive charge this is an SP2 hybridized carbon so carbocations are SP2 hybridize which means they're planer and they have a bond angle of 120° wonderful now how does this relate to your the example of you moving this carbocation is all of your stuff this is all of your possessions where are the friends here R1 R2 R3 so if you had one friend come to help you that means one of these R groups right here is a carbon carbons are your friend nothing else just carbons not hydrogen not chlorine not bromine not oxygen nothing else but carbon so if one carbon is here it's helping you carry this load how we'll get into that if two friends come you have three elements sharing that positive charge and if three friends come you have four elements stabilizing that charge can we ever have four friends though no because carbon can only have four bonds and in a carbocation you must have an open p orbit so that's the fourth nonbonded Bond system right there so we have to have one open Bond now how do we form carbocations and I know you're thinking how does that stabilize and then we're going to get back to that in a moment I just want to let that uh sink in for a couple of minutes so let's try to move this up if possible oh my gosh my iPad is not liking to move things for some reason nope Oh Come come on all right bear with me there's that nope I can't move it up whatsoever so we're have to keep it right here so I'm going to go to another slide and I'm going to show you how we form a caroa so how do carbocations get formed now we're in the section that's called alkenes and ironically that's how a carbocation is going to get formed this carbon carbon bond is going to reach out and attack something and we're going to have it reach out and attack a hydrogen ion now if we go back to that one video about writing organic mechanisms we talked about how a nucleophile Attacks An electrophile a carbon carbon double bond is a nucleophile why four electrons sandwich between two carbons High electron density highly electron deficient species right here so what's going to happen is is that this double bond will reach out and attack that hydrogen when it does we form two intermediates the hydrogen could add on to and I'll call this carbon 1 2 3 and four it could add on to carbon 3 so I'm going to put an aster on that hydrogen and put it right here and then that Carbon 2 becomes positive because the electrons in this Bond attack the proton so if the electrons move over and attack that proton carbon three retains the electrons Carbon 2 loses them that's why we get this positive charge here now could the opposite happen where the double bond attacks the proton and we put it onto C2 absolutely so we can now form this species right here now we just formed two carbocations which one is more stable than the other I'll tell you that this one's formed in 99% and this one's formed in 1% how is that possible a double bond reaching out grabbing a hydrogen it should be statistically 50/50 no when you look at this carbon with three carbon bonds attached that's three friends that makes it more stable this one only has two friends but you might be saying but there's two carbons right here these are your friends calling you on the telephone they don't do anything you have to look at the carbons directly attached to the carbocation now we have clever names for these they're both carbocations the first one we call it a tertiary carbocation why there's three carbons attached and the other one which has two carbons attached we call it a secondary carbocation I know the names are absolutely amazing we can also have a primary carbocation so keeping in mind that little example of friends helping you move which one is more stable the tertiary so a tertiary carbocation is going to form more in a higher amount than a secondary and a secondary will form more than a primary so this is our order of stability for carbocation and we're going to see this more in the Aline reactions video there's going to be a lot more detail in this in that video so all we need to remember here is that a tertiary carbocation is more stable than a secondary and secondary more stable than a primary wonderful what happens after these intermediates we don't care in this video whatsoever that's the next video that you'll be watching what I want to end this video with is how are carbocation stabilized and let's go to another page so how do we stabilize a carbocation so when we're looking at this carbon here is the open p orbital carbocation here are electrons between a carbon carbon likes to send electrons to other elements that are positive so the electrons in this Bond are going to be donated slightly to this C carbocation how much electron density is going to that carbocation versus being exactly in between those two carbons roughly about 4% at Max it's not a lot but 4% is better than nothing so if you have 4% help with one carbon if you have another carbon that's another 4% for eight ooh and a third carbon adding in that's 12% of stabilization that is huge for this carbocation and that's why the more carbons we have directly attached the more inductive effects that we are seeing here what is an inductive effect it's just what I described the ability of carbon to donate electrons to its neighboring or the directly attached caroa let me say that again the directly attached carbocation that carbon can inductively send electrons in that Sigma Bond slightly towards the carbocation versus is being right in the middle between those two carbons that's the inductive effect now and for the inductive effect let me go ahead and draw that little dipole in yellow right here so we can say that was the inductive effect let's see if I can erase the 4% I can't so I'm just going going to obliterate it for a second and write 4% now in blue I want to go ahead and show one of these hydrogens one of those carbon hydrogen bonds there's another one right here and then there's another one right here so there's a lot of them at any given point in time when you think about Newman projections could one of these carbon hydrogen bonds be in the same plane as that carbocation yes only one of them even though there's three hydrogens only one of them can be in the same plane of that p orbital at any given point at time now this is an open p orbital it needs electrons this carbon hydrogen bond when it's in the same plane will bend ever so slightly to give up to 4% electron density into that p orbital just by moving closer to it it's not bonding entirely to it it's just moving ever so slightly and this effect right here is called hyper conjugation so let's go ahead and talk about both of those organic I shouldn't say talk about them but restate what they are the inductive effect is talking about the directly attached neighboring carbons donating a little bit of electron density via the sigma bonds the hyper conjugation effect is talking about carbons and the hydrogens that are on it directly attached to the carbocation bending ever so slightly to give electrons to that p orbital hyper conjug ation is the slight bending of CH bonds inductive effect is the movement of electrons in the carbon carbon Sigma Bond now we have one very important clarification here for hyper conjugation that carbon that's directly attached must be sp3 hybridized if it's SP2 or SP that hydrogen cannot get into the same plane to donate so the carbon directly attached must be sp3 for the hyper conjugation effect be an effect it can still have inductive but it must be sp3 for a hyper conjugation now with that that ends this video over the wonderful world or introduction of alen and the introduction of caradin we will see carbo cadine application in the next video I hope each of you are doing well I recommend going back watching this video again take more notes on it if you have questions email me come to our discussion sections or office hours and I'll be happy to help hope each of you are doing well and I look forward to seeing you all soon