in this video we're going to talk about um how to write a structural formula condensed formula and skeleton formula for organic compounds in your general chemistry class you have learned how to draw the lewis structure small molecules but in organic chemistry it is a totally different uh way to write the structure for organic molecules so let's get started so before we talk about how to draw the structure for organic molecules we need to first understand a certain definition of formulas when you talk about the molecular formula for organic compounds it usually tells what kind of atoms are in the molecules but they don't tell you how they are attached for example if you have a molecular formula for butane it is c4h10 from that c for h10 information one can know one can only say that it is composed of carbon and hydrogens and it has four carbon atoms and 10 hydrogen atoms but it's not telling you how those four hydrogen four carbon atoms are attached together how uh ten hydrogen atoms are attached to the carbon so it's not telling you any attachment pattern informations but when we talk about the structural formula usually that's formula show you the attachment pattern in the molecules for example if you want to have a structural formula for c4h10 it is it will be looking like this where you can see the each carbon connected with another carbon so there are four carbons are connected to each other and hydrogen atoms so three hydrogen atom on the terminal carbons and two hydrogens atoms that are attached on the middle carbon so this is kind of telling you the attachment pattern of hydrogen atoms on carbons or carbon how the carbon connected with another carbon atom so it's giving you more information about the attachment pattern so this type of homologous structural formula now we are going to learn how to write a structural formula from a molecular formula so when you have when you are given a molecular formula um then the first thing you count the number of carbon atoms and then connect those carbon atoms in a row we call carbon backbone then first you need to form a carbon backbone so if you have three carbons then if you have three carbons in your molecular formula then you can write this three carbon backbone and then you add hydrogens to complete four bonds on each carbons so usually the middle carbons they get two hydrogens and in carbon they get three hydrogens so if you add those three hydrogens on the end carbon two hydrogen the metal carbons and that will give you the structural formula for c3 h11 molecular formula so let's practice some couple of more here it says right to structural formula for n alkane ch4c2h6c3h8c4h10 if we have ch4 molecular formula the rule is we have to first write the carbons in the back in a row so that will be your backbone so here we have only one carbon so we can write only one carbon then fill the carbon with four hydrogen atom by single bonds here so now we have a carbon with forcing with four hydrogen so this is the structural formula for ch4 molecular formula now c2h6 we have two carbons we can write two carbons in the back indian rows that would be our backbone then since there are two carbons so each of the carbons can be treated as a end carbon so you need to add three hydrogens on each end carbon so that will give you the molecular structural formula for c2h6 if you have c3h8 again you could write three carbons in a row and the end carbon will get three hydrogen middle carbons will get two hydrogen so you will get this structure if you have c4h10 you can write four carbons in a row this is our backbone now in carbon will get three hydrogens metal carbons will get two hydrogens so as you see here the first carbon got three hydrogens and two middle carbons here each of them got two hydrogen each and this car this is the end carbon you should get three hydrogen so this is the molecular formula for c for as structural formula form of this molecular formula c4h10 so here is the learning check problem write the structural formula for n alkene ac8h18 if you would like you can pause the video and you can answer these questions on your own then you can check your answer with the answer i'm going to show you in a second so you have here in this molecular formula as you see we have eight carbon so you can write eight carbons in a row that would be your backbone and then you just kind of add uh three hydrogens on n carbon two hydrogen on the middle carbon that's pretty much complete your structural formula for c8h18 here is another practice questions um this is uh write the structure from love for in alkane c6 c6h14 again if you use the rule uh it's pretty simple you write six carbons in a row uh that would be your backbone and then you add hydrogens middle carbons get two hydrogens and in carbon you usually get three hydrogens you will have the structural formula for c6h14 next we are going to learn about the condense structure or our condensed formula what is condensed formula sometimes we the structure of organic compounds by simplifying uh in a simplifying way by omitting uh some or all covalent bonds and listing atoms bonded to a particular carbon or sometimes nitrogen or oxygens next to it with a subscript to indicate the number of such atoms so those type of representation are those type of structure we call condensed structure so when you write the content structural formulas we again we uh kind of write the contents formula has the hydrogen attached to each carbon written directly after it so um if you um so so then the question is how do you write the condensed formula so here is the rule attached atoms listed in water so you have to have a central carbon atoms first and then you write in orders so central atoms with attached atoms so let's see some example that will clear some of these little bit more so if you have structural formula this is the structural formula and we see this carbon attached with this carbon discard us to this carbon discarnator to this carbon so the rule is when you are going to write the condensed formula we have to write in this way the attached atoms listed in water so first is the carbon this is the central carbon atoms and it attached with three hydrogens and we usually write the hydrogens right after the carbon directly up to the carbon so carbons and three hydrogen so ch3 and the middle carbons we have here carbon two hydrogen so this is ch2 and again we are kind of writing uh you know you know in water so we are listing here in order so then the third middle carbon here it has two hydrogens here so this is ch2 and the last one ch3 so again when you write a condensed formula from structural formula we usually write the central carbon with the attached atoms and we listed them in water the way it is appearing in the structural formula so ch3 here ch2 ch2 ch3 if you have a double bonds that's perfectly okay again follow normal bonding patterns used to determine the position of multiple bonds so we have here ch2 so right ch2 so next attached to this carbon this is ch2 so it would be ch2 ch2 and if you have uh more than one identical probe attached to the same previous central atoms and we use the parenthesis for example if you have this structural formula you like the condense i like to write the condensed structural formula then what you are going to do you just write this is the ch3 then this carbon bonded with two methyl groups so we have to use the parenthesis again we use the parenthesis when you have ident uh same identical atoms other than hydrogens the ch3 and then this carbon two methyl group here then ch2 and then ch3 so this is the condensed formula for this uh structural formula so that take us to our next lecture problem here it says write the condensed formula for the following structural formula so again we will see this is our the the backbone and the first carbon uh this is the first carbon bonded with three hydrogen so we have to ch3 then it's bonded with next carbon so you have to ride in in order so then it will turn into ch3 ch2 ch2 h2 ch2 ch2 ch2 ch3 as you see here in the condensed formula we are not actually showing the bonds at all right that's the thing you must need to remember we omitting all those covalent bonds here we're just writing the central carbon atoms and test with hydrogens and hydrogens right after the carbon each time and from this information one can also figured out this is bonded with this carbon this carbon bonded with this carbon this carbon bonded with this carbon this kind of wanted this carbon so this is how uh it is actually uh we we did now we want to learn how will you write the structure formula from condensed formula so if you are given a condensed formula how do you write the structure formulas kind of opposite so let's see some example here if you are given ch3ch2ch3 how do you write the structural formula here is the rule so start by writing the first carbon with this attached hydrogens the first carbon here is ch3 hydrogen ch3 carbon so this is the central carbon three hydrogens and then continue adding each successive carbon with its attached hydrogens or brown chain so the next carbon is this carbon so that's a ch2 then next carbon is cst and when you complete when you when you complete when you complete the entire chain then apply rule four bonds per carbon so each carbon should have four bonds to identify double or triple bonds in this case each carbon has already four bonds so there's no double bond or triple bonds so here's another problem you have this structural formula you liked a condensed formula you like to write the struct condensed formula for ah sorry structural formula from this condensed formula again the first carbon is ch3 then add next carbon that is ch2 the next carbon ch2 and then the terminal carbon ch3 so this is the structural formula for this condensed formula now take us to our next learning check problem draw a complete structural formula for this condensed formula again we're going to if you again if you would like to pause this video you can pause this video and try to answer these questions on your own then you can check your answer with the answer i'm going to show you in a second so first is you begin with the first carbon with the test hydrogen so first carbon here is the ch2 hydrogens with two hydrogen then continue adding each successive carbon with its attached hydrogens of brown chain so next is ch then next is ch2 then next is c h and methyl group and then ch2 and ch3 so once you finish constructing the chain entire chain then apply the four apply the rule four bonds per carbon to identify the double bonds as you see here you have these now this carbon and this carbon they do not have four bonds so that means there is a double bond so this would be the final structural formula for this condensed structure here is another problem again you can pause this video and try to answer these questions on your own then you can check your answer with the answer i'm going to show you in a second the first carbon here is ch carbon is bonded with next carbon ch2 uh bonded with next carbon which has nothing and that carbon is bonded with ch2 and then next carbon bonded with two methyl group and then that's the terminal ch3 now you construct you finish constructing this chain uh now you need to use you need to apply the rule uh car each carbon should have four bonds so if you look at here this carbon has only one two bonds this carbon has two bond there must be a triple bond uh between them so that way each carbon will have four bonds so this would be the final structure for this condensed formula now we're going to learn about the carbon skeleton formula in carbon skeleton formula is a type of formula that shows the carbon skeleton of a molecule it is a two-dimensional representation of the bonds between carbon atoms and bonds between functional group so here we are not going to show you the letter carbon or letter hydrogens we're just going to show you the bonds only between carbon atoms or between the r bonds between functional group so whenever you're going to write the carbon skeleton formula you must need to remember each angle beginning and end of the chain represent carbon atoms and hydrogens usually omitted on on carbons included we include the hydrogens when we talk about the functional group for example if you have o h group or nh2 group in that case we say o h or nh2 but in other cases we don't show the hydrogen atoms for example here is the example of a skeleton formula for this structural formula as you see here we have here one two three four five five carbons and each end carbon has three hydrogen metal carbon has two hydrogen and here is a one two three four five carbons so again and carbon angle is our beginning angle angle angle and this end those represent the carbon atoms so we don't show the hydrogens attached to each carbon atoms in usually in the carbon skeleton formulas we show when we have a functional group if there is a oh group let's say here is the oh group then we say oxygen then a single bond and then hydrogens we can show that but in general when you have this hydrocarbon like this then we don't show the hydrogen atoms on on carbon atoms all right so when you have a multiple bonds then if you like to have write the carbon skeleton formula we usually represent that by double line for example we have a multiple bond here so we showed by a double line means it's a double bond triple bond means we will show by triple lines that's how we write this collision formula here's the one example for skeleton formula for benzene so this is the structural formula for benzene six member ring as you see each carbon has one hydrogens if you write the skeleton formula it will look like this you have six carbons in the ring and each angle represent carbon atoms so you have one two three four five six so you have one two three four five six and you have a double bond carbon-carbon double bonds right we represented here by double lines here's a double line here's the double line with double bonds and the hydrogens here on each carbon we we are not showing here in the skeleton formula so that's the skeleton formula so sometimes a benzene ring so we'll talk about that a little bit later in the course sometime benzene ring represented this way and you have six member ring and there is circle in it that represents the double bonds actually delocalize over all six carbon atoms but this is i will talk about later but we are now learning how to draw structural skeleton formula from the structural formula again when you are going to write this carbon skeleton formula make sure you understand each angle beginning and end always depends the carbon atoms hydrogens are omitted on carbons and we only include when we are going to show the functional group when you have a double bonds then we use the double line when you have a triple bond we use the triple line to represent those type of bonds that take us to our next lecture problem here draw a carbon skeleton formula for each of the following compounds so here we have this structural formula for ch3ch3 so if you want to write the skeleton formula for this one then this would look like this so again it's the beginning and then that represents you have two carbon atoms and each carbon atoms bonded with three hydrogens because if you look at here on this carbon the beginning carbon is bonded with the next carbon that's a one bond so this carbon must have three other hydrogens so it's kind of implied that this is ch3 this is ca3 if you want to draw the skeleton structure for this one again we have three carbon atoms we usually arrive in a zigzag fashion so you have this end here a beginning carbon middle carbon and carbon again beginning carbons is bonded with the next carbon so this is a one bond then this carbon must have three hydrogen this is what this case three for middle carbon is bonded with two end carbons that means there are two bonds already so this carbon has ch2000 implied that's why you should read and this carbon is ch3 because this car end carbon bonded with the one middle carbon by one single bond so in order to have four bonds on this carbon so this carbon must have bonded with three other hydrogen so it's kind of implied again here we have the structural formula for butane so you can um if you can have the skeleton formula looking like this you have beginning carbon then middle carbons and then n carbons again beginning carbon is ch3 middle carbon ch2 ch2 ch3 again if you if you if you think why this metal carbon has ch two hydrogens on it you can figure that out on your own easily uh this middle carbon bonded with one end beginning carbon and one metal carbon so there are two bonds so this carbon what you have four bonds must have bonded with two hydrogens if you have this one you can draw the skeleton structure uh quite easily your first beginning carbon is here and then the second one is the right middle carbon and they are connected by double bonds we showed here by double line and again this is the end carbon ch3 carbon so again when you draw the skeleton structure we don't show the carbon hydrogen's bonds just only talk about the carb bonds between carbons and if there is a functional group we would show the bonds between functional groups if we have the six member ring again you can see that all six carbons are bonded together each carbon has two hydrogen atoms if you have this one then again this is something six member carbons and some cases we have carbon carbon double bonds carbon carbon double bonds if you have this one if again you can pause the video you can answer this question on your own so we have here one two three four five six carbons and we want to show the six carbon bonded together by a single line but there is a triple bond damage there should be a carbon-carbon triple bond so this is the first beginning carbon this first beginning carbon second carbon carbon triple the second carbon so here is the second carbon there is the second carbon a third carbon then you have four fifth six then you have four fifth six carbons there so this is how one can write the skeleton formula uh from structural formula that take us to our next lecture problem here draw a complete structural formula for each of the following structure so here we have a reverse problem we are given here the skeleton formula would like to write the structural formula so we can do the same way so we know this is the beginning carbon the beginning carbon bonded with this middle carbon here and so by one bond then this carbon has three other hydrogen so this is ch3 carbons right so and then we have the middle carbon middle carbon bonded with two methyl group and then we have the carbon bonded with the ch2 and then this carbon bond to ch3 so if you if you start drawing the structure structural formula here so this is your beginning carbon that's a carbon with three hydrogens and this is your mix middle one of the middle carbon this is the carbon bonded with ch3 this is ch3 unit and then this is ch2 and this is ch3 if you want you can also show like carbon with three other hydrogen by single bonds that way it would also be the correct structure here we have a five member ring and with a double bonds again you can show that each this carbon is ch2 carbon ch2 carbon ch2 carbon this is ch carbon because you can see this carbon bonded with a double bond here here is yeah you have another bonsai total three bonds so that means this carbon must have bonded with one hydrogen so this is ch similarly this is also ch and this is ch2 because you can see this carbon bonded with this carbon by one bond with this carbon by one bond so we have already two bonds there so this carbon must have another two hydrogen uh two ch bonds so this is why this is ch2 so this is basically all this this is all about all those uh structural formula and condensed formula carbon skeleton formula that can give you an i idea how to draw the structure for organic compounds so that's all for this video