condensed structures that will be the topic of this lesson and uh we're getting into a chapter on molecular representations and resonance and we're going to learn how to draw organic molecules in addition to lewis structures uh we've got what i call condensed structures and then we've also got bond line structures the topic of the next lesson after that we'll talk about what are called functional groups some different uh chemical moieties we call them uh that you know kind of underlies some different chemical reactivities and molecules and then finally we'll top this off with a lesson on resonance now this is my brand new organic chemistry playlist i'll be releasing these lessons weekly throughout the 2020-21 school year so if you don't want to miss one subscribe to the channel click the bell notifications you'll be notified every time i put one of these up all right condensed structures so i've got an example on the board here and again this is organic chemistry it's all about carbon and you'll find out that uh a carbon chain is kind of the backbone of most molecules and in a condensed structure we list a carbon and immediately following it we list how many hydrogens are attached to it is typically how it works and so in this case this first carbon is bonded to these three hydrogens and if we turn this into a lewis structure we'd have a carbon bonded to three hydrogens and then that carbon is bonded to the next carbon in the condensed structure so we'll draw that carbon in he's bonded to two hydrogens so and then he's bonded to the next carbon in the chain notice that our carbons are going to typically end up with four bonds is typically the way it works for a neutral carbon atom and this carbon now has also bonded to two hydrogens and then he's bonded to the next carbon in the chain which is also bonded to two hydrogens and finally that's bonded to the next carbon in the chain bonded to three hydrogens cool and that is converting our cadet structure into a lewis structure and one of the things you'll kind of get in the ideas is uh just a reminder how many bonds different atoms supposed to have and the halogens typically make one bond just like hydrogen so just wanting one more electron to get a filled shell if you will uh oxygens column wants two bonds nitrogen column three bonds and carbons column typically four bonds uh is what we're usually shooting for and again this assumes no formal charge if we got formal charges those number of bonds will change just a little bit and we'll see examples of that in this lesson all right so this is a really simplistic condensed structure and they get a little more complicated than this and you'll find out that in the next two lessons that organic chemists we're just lazy people in general and the truth is we're just really being efficient but i like to say lazy so in this case we're usually going to try and draw as little as possible and so one of the big major tools we use in condensed structures are parentheses now unfortunately we're going to use parentheses in three different ways which is rather annoying and it's not always spelled out explicitly that there are three different reasons to use parentheses we often just start using them and expect you to catch you know catch along at some point in time so we're going to go through those three exact reasons why we might use parentheses and the first one is when you've got a long carbon chain just like we do here and you have these repeating ch2 groups we call these methylene groups there's repeating ch2 groups and rather than write a condensed structure like this which is totally acceptable nothing wrong with this but we can make it shorter and so in this case we can turn this into we'll still start with ch3 right at the end here but instead of writing all three of these ch2 outs we'll write ch2 put it in parentheses and show that there are three of them repeating and we only use this repeating pattern for ch2 groups again called methylene groups and then we'll get right to the end ch3 so that's the first case we're going to use parentheses so but there are two additional cases so but again the only time we're going to use this as a repeating parenthesis here so for repeating pattern is for ch2s not for anything else so that's the first way we're going to use parentheses let's take a look at the next two okay so the second place we'll use parentheses when you've got a long carbon chain and you've got branches coming off the main chain now it turns out that branches coming off that main carbon chain aren't always going to need parentheses if those branches are a single atom like a halogen well then you don't need parentheses you don't use parentheses but if they are multi-atoms if there's many atoms in that branch that's when you're going to need to use parentheses and that's what's going on right here with this ch3 in parentheses this entire ch3 is a branch coming off the main chain so let's turn to this condensed structure once again into a lewis structure so we've got a carbon bonded to three hydrogens we'll start there so bonded to the next carbon in the chain and this carbon right here is bonded not only to a hydrogen but he's bonded to a bromine don't forget that halogens typically form just one bond and in this case because it's just a single atom they don't put it in parentheses it's implied that being a bromine so it can only make one bond it could never go in the middle of the chain because anything in the middle chain's gonna have to be able to make multiple bonds cool and then we'll move on to the next carbon and that next carbon is bonded to just a single hydrogen cool and then it's bonded to the ch3 as a branch coming off the main chain and again because it has four atoms not just one that's why it's showing up in parentheses in this example uh in our condensed structure and then we'll move on to the next carbon in the chain just draw a long bond so i can keep lining this up so bonded two hydrogens and then to the next carbon in the chain bonded to three hydrogens cool so this is the second place we use parenthesis so again the first place was repeating ch2 groups the second place here is multi-atom branches coming off the main chain all right this last example will use parentheses is really just an expansion or a special case of the second way we used them and that was for branches and in this case we'll use it for branches but in this case when you see a little subscript here it means you have multiple of those branches that are identical coming off whatever carbon they're attached to and so in this case notice we only need to use these for again multi-atom branches so same thing in the second rule we're only going to use parentheses around branches that have multi-atoms and now we see that we can actually show that there are multiple identical branches attached to the same carbon using parenthesis in this fashion so in this case we've got this carbon right here and that carbon right there is bonded to one hydrogen but he's also bonded to two of these ch3 so we've got one here and one here and i really could have drawn these in any any pattern it's all the same thing cool and then this carbon's bonded over to the next carbon which is bonded to two h's which is bonded to the last ch3 here cool and that is our lewis structure matching up with this condensed structure all right next part of condensed structure we want to focus on is when we've got to add pi bonds into the structure and the idea is that you know if you set up your skeleton as depicted by your condensed structure if you know not every atom's got a filled octet if you've got two adjacent atoms that both need more electrons you'll typically give them at least one pi bond like a double bond or potentially even two pi bonds uh and like a triple bond between them as as the case may deem so let's take a look at this here so this first example again we start off with a carbon bonded to three hydrogens cool bonded to the next carbon in the chain which is bonded with two hydrogens which is bonded to the next carbon in the chain which is bonded to one hydrogen which is bonded to the next carbon in the chain which is bonded to one hydrogen which is bonded to the next carbon in the chain which is bonded to three hydrogens and if we go back and examine this structure we'll notice that this carbon right here has only got three bonds this carbon right here has only got three bonds and they don't have any charge on them and so typically carbon again with no charge got four bonds well two adjacent atoms both short one bond the easy solution is to then put a double bond between them cool and it just we had two atoms adjacent to each other that both needed one more bond quick solutions to put a pi bond there so similar fashion right here so start off again with a carbon bonded of three h's bonded to the next carbon in the chain bonded to two h's so next two carbons in the chain bonded finally to the last carbon bonded to three h's and then similar to the last example we now got here two carbons right next to each other that both only have two bonds again there's no formal charges shown on them so they really should get four bonds and so the quick solution to get them both two more bonds is to have them share two more bonds in this case two pi bonds and there we've got a triple bond so this is kind of how you deduce that you've got either a double or a triple bond in one of these condensed structures you just got atoms next to each other that both don't have a filled octet all right we'll find that oxygen is a common atom and a lot of organic molecules and when you've got a condensed structure with oxygen in it as you do here so what you'll find is that if you try and oxygen can make two bonds first of all that's pretty typical of auction technique auction can make three if he's got a positive formal charge but neutral oxygen typically makes two bonds and when oxygen makes two bonds that means he actually can go in the middle of the chain of atoms so key again is that if you only make one bond you can't go in the middle of a chain because you've got to make at least two to branch in two directions to go in the middle of the chain and auction can totally do that so the question is how can you tell if auction's in the middle of the chain or if oxygen is a branch coming off the chain and it's tricky because oxygen is just a single atom so we don't have to put him in parentheses or anything like that if he's a branch and so a condensed structure is not going to just come out and tell you if the auction goes in the middle of the chain or is a branch off the chain and so usually i say default trim in the middle of the chain but if you see a bunch of atoms that are not getting their filled octets you might realize he's going to end up being a branch instead so let's take a look at the first one here so we've got a carbon bonded to three hydrogens bonded to another carbon with just one hydrogen bonded to another carbon with just one hydrogen bonded to a carbon bonded to an oxygen bonded to a carbon with three hydrogens so if we start looking at this here so we've got some problems here these this carbon right here has only got three bonds this one's only got three bonds this one's only got two so we might be like well we've seen this pattern before let's just put a double bond in here and these two are now happy but the problem is we're never going to get that carbon happy he needs two more bonds but the atoms next to him now don't need any more bonds so this is usually kind of where where you get to a point where you deduce oh that oxygen probably wasn't supposed to go in the middle of the chain but be a branch coming off the chain that's we're going to do here so i'm going to erase this right here we're now going to make that auction a branch coming off the chain and then connect this carbon to the next one in the chain right over here cool and so now if we go back and examine this one more time so we see that we've got that carbon which only has three bonds needs one more and we've got the oxygen right next to it which only has one bond and needs one more and so once again just like we had over here we've got two adjacent atoms that both need one more bond and the easy solution is to put a double bond in right there cool and this is an example of one of the functional groups we'll study later in this chapter called a ketone all right so let's take a look at this one as well so it'll work out pretty similar the one we just did so start this off carbon bonded to three hydrogens bonded to the next carbon which is bonded at two hydrogens bonded to the next carbon which is also bonded to two hydrogens bonded to the next carbon which is bonded to an oxygen oxygen a hydrogen so oxygen oxygen hydrogen and again sometimes though oxygens are in the chain and sometimes they're a branch coming off the chain so but if we take a look here so these three carbons are all happy they got four bonds each but this one's only got two and then we got these oxygens here that both already have two bonds which is their normal number so the only atom that's not happy is that carbon he needs two more bonds and there's nobody next to him who needs any more bonds so we can't just throw pi bonds in there and so in this case again that's evidence that we probably should take one of those auctions off and make it a branch and then bond the carbon to the last oxygen there and by doing it this way similar to what we did in this last example we end up with two atoms carbon in this case with three bonds needs one more oxygen with only one bond needs one more but two atoms next to each other both needing one more bond and the easy fix is to put a little bond here we'll find out that this is an example of a carboxylic acid i believe we did one of these examples back in chapter one as well and i said hey we'll talk about these later in chapter two well we're talking about them now but we'll talk about them again in the third lesson in this chapter as well