you're probably wondering why i told you not to watch this video and i wanted to try an experiment i wanted to see if people would actually watch the video after receiving a message not to do so it's sort of a reverse psychology thing and it's been said that if you tell someone not to do something they will actually do it which is weird but i wanted to try this out and see you know if this will actually work and so i would like to ask you to do something if you have a moment that is if you're not too busy and that is to post a comment in terms of why you chose to watch this particular video was it because you wanted to learn organic chemistry or was it out of curiosity because the video told you not to watch it what was the reason out of all of the other videos that you could have clicked on why did you choose to watch this particular video so let me know in the comment section if you have time now the title of this video is organic chemistry so i'm going to stay true to that and teach you orgo chem so for those of you who want to get an introduction into organic chemistry if you're about to take it in the next upcoming semester you came to the right place let's begin the first thing i'm going to do is teach you how to draw lewis structures of common compounds so let's review some basic things in the periodic table so in group 1 you have elements like hydrogen lithium sodium and these elements they contain one valence electron that is the number of electrons in the outermost energy level and as such these elements typically form one bond whenever you see hydrogen in a molecule keep this in mind hydrogen can only form one bond if you were to see beryllium which is in group two it has two valence electrons that it can give away you'll see typically it will form two bonds boron which is on this side on the right side of the periodic table is in group 3a it likes to give away three electrons and so it tends to form three bonds not always though but ideally if it's neutral it's gonna form three bonds if it has a negative charge it's gonna form four bonds but for elements or compounds that don't have a charge the number of valence electrons is related to the number of bonds that they form carbon for example has four valence electrons and it likes to form four bonds now as you get to the right side of the periodic table towards the nonmetals the trend changes nitrogen for example has five valence electrons but in its neutral state when it doesn't have a charge it likes to form three bonds and the reason for this is because the elements on the right the non-metals they like to acquire electrons they want to get eight electrons to satisfy the octet rule and so that's why nitrogen likes to form three bonds so that it can get those three electrons it needs to get to eight so i'm going to put it in red that nitrogen likes to form three bonds oxygen has six valence electrons it needs two more to get to eight so oxygen likes to form two bonds fluorine has seven valence electrons it only needs one more to get to eight so fluorine likes to form one bond and this is true of the other halogens like chlorine bromine and iodine ideally they like to form one bond now there are exceptions to this rule particularly if you have a molecule where bromine or chlorine is the central atom in that case it may form more than one bond but typically in organic chemistry you'll see that most of the time these elements like to form one bond elements under oxygen like sulfur selenium they like to form two bonds phosphorus it likes to form three now remember these are just general trends that you'll see in organic chemistry now let's focus on these two elements nitrogen and oxygen so remember nitrogen likes to form three bonds if it doesn't have a charge if it's neutral and oxygen likes to form two bonds in its neutral state so we can illustrate that with ammonia ammonia nh3 has one lone pair and three bonds in this state nitrogen doesn't have a charge and so it has its ideal number of three bonds now when nitrogen loses a hydrogen it's going to have two bonds but it's going to have a negative charge so in this case it doesn't follow the trend because it's not in its neutral state it has a charge or if nitrogen acquires a hydrogen atom or rather a hydrogen ion it's going to acquire a positive charge once again it doesn't have its idle number three bonds and so that's why it has a charge so that general rule where you can look at the table and determine the number of bonds that an element prefer to have that rule applies when the element is in its neutral state now let's consider the structure of water of h2o in this molecule there is one oxygen atom and two hydrogen atoms as you can see in this structure oxygen doesn't have a charge because it has its ideal number of two bonds which is what it needs to get to eight electrons now if we were to draw hydroxide it will have a charge a negative charge because it doesn't have its idle number of bonds it only has one bond now if it has more than its ideal number it's going to acquire a positive charge so whenever oxygen has three bonds it's going to have a positive charge whenever it has one bond it will have a negative charge now for those of you who want to understand how this works with more examples including the exceptions check out a video that i created on youtube it's entitled lewis structures it's a very big video it's about two hours long so you can't miss it and if you type in lewis structures organic chemistry tutor it should come up but in that video i go deeply into why this works the way it does with many examples as well as the exceptions and understanding the reasons behind why those exceptions exist so if you want a deeper understanding of that feel free to take a look at that video when you get a chance now let's review a few things when you see nitrogen as an element in a lewis structure know that it likes to form three bonds and it will have one lone pair in its neutral state if you were to see oxygen it typically has two bonds and two lone pairs or if you see another element with two bonds then you know that there's going to be two lone pairs missing now if you see an element like fluorine with one bond then you need to know that it has three lone pairs on it and if you see carbon make sure you know that carbon likes to form four bonds in organic chemistry you're going to see a carbon a lot so make sure you know this let's go over some examples let's say if we wish to draw the lewis structure of methane how can we do so now remember carbon likes to form four bonds and hydrogen likes to form one bond so the only way to put this together is to draw four bonds around the carbon atom and each bond is attached to one hydrogen atom and so that's how we can draw the lewis structure of methane now what about ethane ch3ch3 so when you see a condensed structure like this draw it from left to right so starting with the first carbon on the left let's draw that it has three hydrogen atoms attached to it and so let's draw the three hydrogen atoms starting from the left now it's attached to another carbon atom that has three hydrogen atoms attached to it and so that's how you can draw the lewis structure of ethane now let's say if we want to draw the lewis structure of propane ch3ch2ch3 so starting with the carbon on the left it has three hydrogen atoms attached to it and then it's attached to another carbon that is the ch2 carbon so that carbon has two hydrogen atoms attached to it next it's a ch3 so we have another carbon atom with three hydrogen atoms attached to it and so that's how you can draw lewis structures of alkanes an alkane is an organic molecule that consists of carbon and hydrogen where there are no double bonds or triple bonds and now cane is said to be saturated it is filled to the limit with hydrogen atoms it contains the maximum number of hydrogen atoms it can possibly hold and so this is a hydrocarbon that is said to be saturated now what about the lewis structure c2h4 how can we draw it so we know that there are two carbons and those two carbons have to be attached to each other but we can't put the four hydrogen atoms on the right side because carbon cannot form five bonds so that's not going to work when you see a situation like this the best thing to do is to distribute the number of hydrogen atoms equally among both carbon atoms because they're the same element and so they're going to have the same affinity for the hydrogen atoms so it makes sense that you should share them equally so we're going to put two hydrogen atoms on the right side and two hydrogen atoms on the left side keeping in mind that hydrogen can only form one bond now at this moment carbon only has three bonds so if we were to highlight one two three but carbon needs to have four bonds the only way to rectify the situation is to put a double bond between the carbon atoms and so now every carbon atom has a total of four bonds around it and every hydrogen atom has a one bond so once those conditions are met you know you have the right lewis structure now this particular molecule is known as an alkene an alkene is a functional group where the organic compound has a double bond it's also known as an unsaturated compound the reason why it's unsaturated is because unlike an alkane it does not contain the maximum number of hydrogen atoms that it can hold so it's unsaturated now let's try this one c2h2 go ahead and draw the lewis structure based on the previous example so in this case there are two carbon atoms and there's two hydrogen atoms which will place them out on opposite sides with symmetry now hydrogen can only form one bond and carbon likes to form four bonds so the only way we can make that work is by putting a triple bond in the middle and so this is known as an alkyne it's also an unsaturated hydrocarbon alkynes contain triple bonds now you need to know that trouble bonds are very strong they're stronger than single bonds but in terms of length they are very short single bonds are very long but they're weaker triple bonds are stronger but they're shorter now the way i like to think of the strength of a triple bond is like a pencil it's easy to break one pencil like a single bond but it's harder to break three pencils at the same time because three pencils are stronger and the same is true for a triple bond it's very difficult to break all three bonds compared to just breaking one bond so triple bonds have more bond strength than an individual single bond now i want to go over some common names of alkanes so the first one which we talked about already this is known as methane the second one which contains two carbons c2h6 this is known as ethane alkanes they have the general formula c n h two n plus two now we talked about c2h4 and so this was an alkene but notice that it has two carbons so this is called ethene and the general formula for an alkene with one double bond is cnh2n now the next one that we went over was an alkyne and the example that we use was c2 h2 the general formula for an alkyne is cn h 2n minus 2. and so this particular alkyne has one triple bond and any other alkynes with this formula will have only one triple bond now when dealing with three carbons the name is propane so if we have c3h6 this would be propine it will be an alkene or if we have c3h4 that would be propion because it has a triple bond and so it's an alkyne now for an alkane with four carbon molecules i mean four carbon atoms rather this is known as butane and for a molecule with five carbon atoms this would be pentane and for an alkane with six carbon atoms this is known as hexane c7 that corresponds to heptane as an alkane so that's c7 h16 c8 h18 this is known as octane c9 h20 this is known as non-name and c10h22 this is called decane deca is 10 nana is 9 octa is 8 hepta is 7 hexa is six penta is five and so forth now let's try another example ch3oh how can we draw the lewis structure of this particular compound so starting from the left we have a carbon atom that is attached to three hydrogen atoms each of which can only form a single bond now we do have an oxygen atom and if you recall oxygen likes to form two bonds and it's going to have two lone pairs so that's how we can draw the lewis structure for this molecule and whenever you see an oh group at the end the functional group is known as an alcohol now if you recall a one carbon alkane is known as methane but now the functional group is not an alkane anymore it's an alcohol so instead of saying methane this is going to be called methanol but as you can see the structure of the name meth is still there because methyl or metha is associated with one carbon atom the ol tells us that it's an alcohol rather than an alkane let's consider another example ch3 ch in parentheses oh and then ch3 so how can we draw the lewis structure of this particular molecule and at the same time what do you think the name of the molecule will be so starting from the left side and working our way towards the right side on the left we have a carbon with three hydrogen atoms and then we have another carbon with a hydrogen atom which i put at the bottom and then it also has an o h when you see that in parenthesis that means that the previous carbon is attached to an o h group so we can draw o and then h and remember oxygen when it has two bonds will typically have two lone pairs and then to the right we have a ch tree so every carbon atom in this molecule has four bonds every hydrogen atom has one bond and oxygen has its desired number of two bonds and so by understanding those basic principles it will help you to quickly draw the lewis structure of an organic molecule now let's talk about naming this molecule so anytime you see an oh group you know you have an alcohol on your hands now r that's basically the rest of the molecule so you don't have to worry about it but anytime you see the o h group it's an alcohol now if we count the number of carbon atoms let's call this carbon one two and three there are three carbon atoms which is associated with the name propane probe is associated with three now we do have an alcohol so we're gonna take off the e and add ol so this is going to be called propanol now the last thing we need to do is identify the position of the alcohol or the oh group the oh group could be on carbon 1 but it's on carbon 2 and so we need to specify the position of the oh group in this molecule so this is going to be called 2-propanol if the o-h group was on carbon 1 it would be called 1-propanol so this is how you can name this particular alcohol now let's talk about ethers ethers are the next functional group that you need to be familiar with if you're going to take organic chemistry and let's start with this example ch3och3 so let's begin by drawing the lewis structure so on the left we have a methyl group or a ch3 group and the carbon is attached to an oxygen which is attached to another carbon atom with three hydrogen atoms on it and when dealing with oxygen whenever it has two bonds it's going to have two lone pairs and so that is the lewis structure of this particular ether now to name it we're gonna use the common name first on the left side we have a methyl group and on the right side we have a methyl group and since we have two methyl groups on this ether we can call it dimethyl ether di means two now what about this particular ether what is the common name for it ch3ch2och3 let's not worry about the lewis structure for this example now on the left side we have two carbons so that is an ethyl group and on the right side we have a ch3 so that is a methyl group now to write the common name we need to put this in alphabetical order so it's going to be called ethyl methyl ether so that's the common name for it now let's focus on the iupac name of this particular ether so i'm going to draw it differently so attached to this carbon we have an och3 group so you can call this the substituent and it's located on carbon one this is the parent chain it's the longest carbon chain in that molecule so this group right here is called ethane because we have two carbons and the och3 group as a substituent is known as a methoxy group so another way in which you can name this molecule you can say it's 1 methoxy ethane now it really doesn't matter if the och3 group is on carbon one or carbon two because no matter which way you count it the first one is going to be carbon one so if the oh excuse me if the och3 group was on this carbon it would still be one methoxy ethane so therefore the one is not necessary in this case so we could simply call it methoxy ethane let's work on another example with ethers so go ahead and name this particular ether both the common name and the iupac name so let's start with a common name on the left side we have a propyl group and on the right side we have an ethyl group so putting it in alphabetical order e comes before p so it's going to be ethyl propyl ether now i'm going to redraw the structure like this so the longest chain is three carbons and i'm going to put the substituent the och2ch3 group on top now if you want to you can convert this to a line structure these three carbons can be represented like this and so every endpoint that you see here represents a carbon atom so at the last one on the right we can write the och2 ch3 group so let's call this carbon one two and three you wanna number it in such a way that the substituent is given the lower number so you don't wanna number it this way because the substituent will be on carbon 3 rather you want to count it from right to left in this example so that the substituent is on carbon 1 it's given a lower number so this right here is called an ethoxy group so instead of a methoxy it's ethoxy since we have two carbons in that substituent group and we're still dealing with an ether now it's located on carbon one and the longest chain is a three carbon chain which is going to be called propane so to put it together it's going to be called one ethoxy propane and so that's how you can name that particular ether now how would you draw the lewis structure for this molecule go ahead and try that so let's start with the left side so we have a methyl group that is a carbon with three hydrogen atoms and that's attached to a ch2 which is attached to a carbon all right so now let's stop let's focus on what we have here now remember carbon likes to form four bonds and oxygen likes to form two bonds so what can we do here well we can't write it like this because this is not going to work the carbon will only have two bonds and so that is not the ideal situation that we want to make this work the only way in which the carbon atom will have four bonds and the oxygen atom will have two is to put a double bond between the carbon and the oxygen that's the only way this is going to work and so as you can see every carbon atom has four bonds every hydrogen atom has one bond and the oxygen has two bonds and two lone pairs this is known as a carbonyl functional group whenever you see a c double bond o it's called a carbonyl functional group now this particular molecule also has a special name it's called a ketone whenever you have a carbonyl functional group in the middle of the chain that is it's not at the end it's called a ketone if it's at the end let's say at the last carbon or the first one it's known as an aldehyde now let's go ahead and name this particular ketone so which way should we count the carbon atoms from left to right or right to left if we count it from left to right the carbonyl group will be on carbon 3 but if we count it in the other direction from right to left it's going to be on carbon 2 and so we're going to go with that direction so this is going to be called 2 butanone now if the carbonyl group was on carbon 1 or 4 as we said before it's going to be an aldehyde not a ketone if the carbonyl group was on carbon 3 and we would have to count it this way it would still be called 2-butanone so therefore the two is not necessary we can simply call this butanol because if the carbonyl group was on this carbon on this carbon you would simply count it in different directions but the result will be the same it would still be called be unknown in a situation like this where the result is the same you really don't need to write the number it's not necessary now let's try another example how can we name this particular molecule so we have a line structure and we need to count it starting from the right side because the carbonyl group is closer to the right and so we could see it it's on carbon three and we still have the ketone functional group now for seven carbons we have the name heptane but because is a ketone instead of saying heptane we're going to say heptone or not heptone but we're going to drop off the e and add on so it's heptanone and we're going to put a 3 in front of heptanone because the carbonyl group is located on 3. now this time we need to specify where the carbonyl group is located so the answer is three heptanone now let's move on to our next example let's draw the lewis structure of ch3 cho anytime you have this if you see cho rather than o h o h is typically associated with an alcohol but c h o when you see that you have an aldehyde this is very specific for an aldehyde now let's draw it so let's start with the methyl group on the left and so we have a ch3 attached to a carbon now how do you think we can [Music] write the lewis structure of c h o now we can't write it like this because hydrogen cannot form two bonds and it doesn't make sense to write it like this like an alcohol because carbon will only have two bonds so we need to make a carbonyl group if we do it like this now carbon has four bonds oxygen has its desired number of two bonds and hydrogen has one so anytime you see cho it's basically a carbonyl group at the very end now we have a two carbon molecule so instead of saying ethane we're going to drop off the e and replace it with a out and so that's how you name an aldehyde so this is f and out let's try another example so how can we name this particular aldehyde so this is going to be carbon one two three four five so instead of saying pentane we're going to drop off the e and replace it with a out it's pentandal now we don't need to say one petanol because the aldehyde functional group is always at the end of the chain so the one is always going to be there unless it's a substituent now what about this one ch3 ch2 co oh so whenever you see this functional group c o o h you have something known as a carboxylic acid it's a weak acid but that's the function of group four so if you see r c o o sometimes you'll see it as our co2h and it's the same thing it's a carboxylic acid so let's go ahead and draw the lewis structure at least just the the right side so the left side i'm going to leave it as ch3ch2 because you know how to draw already now for the last part we have a carbon we have two oxygen atoms one of which is going to be a carbonyl group and the other part is going to be an o h group and so carboxylic acid is the combination of a carbonyl group and a hydroxyl group or an o h group and so that's how the lewis structure will look like if you expand it now to name it we have a three carbon carboxylic acid so three carbons is associated with the word propane but instead of saying propane we will drop off the e and add oak so it's called propanoic acid and that's how you could name carboxylic acids let's try this example go ahead and name this particular carboxylic acid so we have a total of eight carbons which is associated with the name octane but it's going to be called octanoic acid and as you can see the carboxylic acid is always on position one thus there's no need to say one octanoic acid it's simply octanoic acid next up we have this molecule ch3 co2 ch3 this is known as an ester so if you see this function or group r and then coo and then another r group you have an ester so to draw the middle portion we have a carbon with a carbonyl group and an oxygen that's attached to a ch3 and so typically you'll see this associated with esters the difference between an ester and a carboxylic acid is in a carboxylic acid this whole group will be a hydrogen if it's a carbon with some other stuff attached to it then it becomes an ester now to name it we're going to start with this side the carbon that doesn't have two oxygens attached to it so this group is a methyl group now on the left side we have two carbons including the one that has two oxygens and so that group is called instead of saying ethane it's ethanoate but when name in esters the alkyl group goes first so it's going to be called methyl ethynoid so that's how you name this particular ester now the next functional group is an amine and so for amines you'll have the rnh2 group so let's go ahead and draw that particular structure so here is the ethyl group and we have a nitrogen attached to two hydrogen atoms and as recall nitrogen likes to form three bonds in one lone pair so that's how we can draw this particular amine and the common name for it in this example is ethyl amine because we have an ethyl group attached to an nh2 group now if you're dealing with iupac nomenclature the nh2 group as a substituent is called amino so you can also say this is amino ethane now let's say if we had a longer chain and we have the nh2 group on carbon 2.
so for 5-carbon chain this would be pentane but we can say 2 dash amino pentane so that's how we can name that particular amine now the next functional group you need to be familiar with is an amide and the amide is similar to an amine the only difference is there's a carbonyl group between the r group and the nh2 group making it an amide so this particular amide with four carbons is going to be called instead of saying butane we're going to drop off the e and add amide so collectively we're going to call it butanomide now some other functional groups that you want to be familiar with is the nitrile another one you'll see in organic chemistry is the acid chloride and finally another one is the benzene ring also known as an aromatic ring so this bezzy ring the formula c6h6 every carbon atom has one hydrogen atom attached to it so that's a benzene ring also known as an aromatic ring so those are some other functional groups that you want to add to your list now let's move on to something called formal charge you need to be able to calculate the formal charge of an element so let's start with oxygen what is the formal charge of the oxygen shown in the picture is it positive one is it negative one is it zero or neutral is it negative two positive two what is it to calculate the formal charge of an element it's going to equal the number of valence electrons in the free element minus the number of bonds and dots that you see in the picture so naturally oxygen has 6 valence electrons it's in group 6a of the periodic table in this example it has one bond as we can see here and there's three lone pairs which is equivalent to six dots and so one plus six is seven and so we have six minus seven which is negative one and so this oxygen has a negative charge so anytime you see oxygen with one bond and three lone pairs you need to put a negative formal charge on it now what about this example so let's say we have r o h and another h with a lone pair what is the formal charge on oxygen so using the same formula the formal charge is going to be the number of valence electrons minus the sum of bonds and dots on that element so the formal charge for oxygen is going to be the six valence electrons that it has and in this structure we could see a total of three bonds and one lone pair or two dots now three plus two is five six minus five is one so in this case whenever oxygen has three bonds and one lone pair it's going to have a positive formal charge now let's try nitrogen so what if we have r and h with two lone pairs what is the formal charge on the nitrogen atom go ahead and try that one nitrogen is found in group 5a of the periodic table so it has five valence electrons in this structure it currently has two bonds and it has four dots or two lone pairs so two plus four is six and five minus six is negative one and so the nitrogen has a negative formal charge in this example another topic that you will encounter in your first semester organic chemistry course is resonance structures so here's what a typical problem will look like you'll be given a structure in this case this is ethanoate also known as acetate and you're told to draw the resonance structure of the one on the board and here we have a negative formal charge on the oxygen to draw a resonance structure what you need to do is you need to realize that you're allowed to move electrons but not atoms and you need to use something called curve arrow notation to show it to show the movement of electrons a full arrow represents the flow of two electrons a half arrow represents the flow of one electron so we're going to take this lone pair these two electrons use it to form a double bond also known as a pi bond and we're going to break this pi bond and put two electrons on the other oxygen and we could use a double arrow to indicate that the next structure is a resonance structure and so this is how the other resonance structure is going to look like so now the oxygen on the right has two lone pairs because it lost one and the other one it gained one so it has three and so that's how we can draw the resonance structure of acetate now let's try another example let's draw the resonance structure of an amide go ahead and try it what we could do is take a lone pair from the nh2 group form a pi bond and then break the pi bond of the carbonyl group and so the resonance structure will look something like this in this case the oxygen now has a negative formal charge and the nitrogen has a positive formal charge by the way which of these two resonance structures is the major resonance contributor which one is more stable in the other example in both resonance structures the oxygen had a negative charge so they were equally stable and this one is different in the first example both the oxygen and the nitrogen were neutral now the oxygen has a negative charge and the nitrogen has a positive formal charge and whenever you see the situation whenever you have separation of charge it creates a less stable situation and so the less stable resonance structure is known as the minor resonance structure and the more stable one is known as the major resonance structure the actual molecule is really a hybrid between these two however the actual molecule it looks more like the major resonance contributor and less like the minor resonance contributor even though it's somewhere in between it's going to look more like this molecule now what about this example so let's say we have a double bond actually two double bonds and a carbon with a negative charge a carbon with a negative charge is known as a carb anion a carbon with a positive charge is known as a carbocation so in this case how can we draw the lewis structure or rather the resonance structure of this particular ion what we need to do is take the lone pair and move the electrons towards the double bond we can break this pi bond put two electrons on this carbon and so the first resonance structure that we can draw will look like this and now we have the negative charge on that carbon and then we could repeat the process we can move the negative charge two carbons further to the left and so in this example we can draw a total of three resonance structures including the original one and so anytime you see a lone pair next to a double bond that's what you can do if you wish to draw the resonance structure now let's say we have a six carbon ring with a positive charge on the outside draw the possible resonance structures for this one now in this case we're going to move the pi bond to or towards the carbocation so the first resonance structure that we can draw will look like this so now the pi bond is over here and the plus charge is going to move to the carbon that lost the bond which is that carbon at the top so like the negative charge in the last example you'll find that the positive charge will jump every two carbons towards the double bond that moved and so we could break this pi bond move it here and this will give us a new resonance structure which looks like this in this case so now the plus charge is at the bottom left and we can draw one more resonance structure for this example let's take this double bond move it here so that's a basic intro into resonance structures now for those of you who want more examples in this topic feel free to check out my new organic chemistry video playlist i do have an old one but check out the new one and i have some videos on resonance structures drawn lewis structures naming compounds so you can check that out if you want to i'm going to paste the link of the new organic chemistry video playlist in the description section of this video so once you access that playlist you could find the specific topic that you need help with so feel free to take a look at that when you get a chance now let's spend a few minutes naming alkanes how would you name an alkane that looks like this let's focus on iupac nomenclature the first thing we want to do is count the parent chain and we have a methyl group on carbon 3. so first let's name the parent chain which is hexane because it has six carbons and we have a methyl group on carbon three so this is going to be called three methyl hexane and so that's how we can name that particular alkane now what about this one we need to number it from left to right you want a number in such a way that the substituents the two methyl groups contain the lowest numbers possible so right now we have a methyl on three and the other one on four if we were to name it in the other direction or rather count it in the other direction we would have a method group on four and five three and four is less than four and five so always number the carbon atoms in such a way that the substituents have the lowest numbers possible so we have a seven carbon parent chain and so it's going to be called heptane and we have two methyl groups so it's going to be dimethyl because we have two of them and it's located on three and four so it's going to be three comma four dash dimethyl heptane you should use a comma to separate numbers and use a hyphen to separate a number and a letter when naming alkanes using iupac nomenclature now let's try another example so let's say we have these two groups how would you name it now first we need to decide which way to count so let's count it this way and let's write the name of the molecule that results so if we were to count it this way we would have a methyl on carbon 4 and this substituent has two carbons on it and so that's going to be an ethyl group so we have an ethyl on carbon 5.
