hello everyone my name is brent kadrowski and this organic chemistry video is going to cover understanding and drawing condensed structural formulas to understand this video you're going to need a basic understanding of lewis structures once you have that you should be able to understand the condensed structural formula concepts in this video condensed structural formulas are abbreviated versions of lewis structures they leave out bonds and lone pairs and they convey the same connectivity information as lewis structures but they're more compact and easier to draw this is important if you're trying to draw them in a word processing program like microsoft word or google docs or some other text based format i have two structures here that i'm going to use to illustrate condensed structural formulas on the left is butane and in this structure i've drawn in all of the bonds as is typical for a lewis structure in condensed structural formulas atoms that are bonded are grouped together for example on the left side of the molecule there's a carbon that's bonded to three hydrogens this group becomes ch3 where we draw out the c and the h and then we put a subscript three behind it to indicate that there are three of them this is a bonded group now we're going to move down the chain and take a look at the next atoms attached next there's a c with two h's attached so we represent that as ch2 with the subscripted two moving down the chain there's another carbon attached to two hydrogens which is represented as ch subscript two followed by a carbon attached to three hydrogens which is represented as ch subscript three this is a condensed structural formula for butane it doesn't contain any bonds but it does convey connectivity information it's important to note that the h's are shown together but they're not bonded to each other each hydrogen only makes one bond carbon makes four bonds and it's important to keep these rules in mind when you're interpreting condensed structural formulas in condensed structural formulas groups that repeat can be represented by parentheses and a subscript number to indicate the number of repeating units for example in this molecule in the middle there are two ch2 groups that repeat so this could be represented by replacing the ch2ch2 with a ch2 and a parenthesis with a 2 around it to indicate the same thing it just takes up less space next we'll look at the example on the right in a similar way we're going to work from left to right to assign the condensed structural formula in this molecule of ethanol this is ethyl alcohol so on the left there's a carbon attached to three h's we're going to call that a ch3 group so c h with a three subscripted then we'll move on to the next part which is a carbon in the middle with two hydrogens attached that will be represented as ch2 with the subscripted two and finally there's the oh group and notice here we're drawing oh but we're not indicating the lone pairs on oxygen they're important but they don't get represented in the condensed structural formula here we're going to look at another example of converting a lewis structure to condensed structural formula a lot of times there's more than one correct condensed structural formula that you can write for a given lewis structure and that's certainly the case with this example what i'm going to do here is just show you a couple of ways that you can represent it in a very condensed form but there are other ways that you could represent it as well one strategy is to recognize that there are three ch3 groups attached to a central carbon and you can represent those with a ch3 in parentheses with a subscript three then you just finish the structure by drawing ch to represent the central carbon and hydrogen attached another equivalent way to represent this molecule would be to first write hc to represent the central carbon and its attached hydrogen and then draw the three ch3 groups afterwards both representations mean the same thing and they're equally correct this slide we're going to talk about how to take a condensed structural formula and convert it into a lewis structure this is also a very important skill here's an example of a condensed structural formula that students have had problems with in the past we're going to go through this step by step and describe how to convert this into a lewis structure so we'll start with the left side of the molecule and read from left to right the first thing to notice is that this molecule starts with ch3ch2 parentheses three that means there's three of these groups attached to a central carbon atom we're going to start with the central carbon atom and draw that in first then to that central carbon atom we're going to draw the various groups that are attached the three ch3 groups then to that central carbon atom is also attached a carbon with two h's we're going to draw that next following along with the structure that carbon is attached to a carbon that's attached to an h and also a ch3 group that's indicated in parentheses moving along the chain there's another ch and that ch is attached to two ch3 groups this slide talks about how to handle double bonds and condensed structural formulas here's an example of an alkene this is a molecule that contains a carbon-carbon double bond often times with carbon-carbon double bonds people will draw in the cc double bond as a pair of lines between a couple of carbons here's an example of how to translate this lewis structure into a condensed structural formula we'll start on the left with the ch3 group then follow up with the ch then we'll draw a pair of lines and another ch and that pair of lines indicates the location of the carbon-carbon double bond we'll just finish up then with a ch2 ch3 you'll also potentially see this molecule drawn as in the following example here it's just the location of the h and the c that have been swapped the connectivity information is the same the reason people might do this is to just emphasize that it's a carbon-carbon double bond for clarity mostly it's an aesthetic preference over on the right we have an example of a carbon oxygen double bond by convention most of the time the co double bond isn't drawn in although you may see it from time to time here's an example of how to translate this ketone structure into a condensed structural formula we'll start on the left with the ch2 group and work our way to the right the c double bond o group is simply drawn as co in the condensed structural formula finally drawing ch3 completes the molecule when you're reading this condensed structural formula it's important to understand that the oxygen is doubly bonded to the carbon highlighted in purple it isn't bonded in any way to the carbon that's highlighted in red sometimes people will clarify this by drawing the oxygen in parentheses so sometimes you'll see a variation of the condensed structural formula drawn like this on the next slide we're going to go through a couple more examples of carbon-oxygen double bonds we'll start off with a carboxylic acid which has a c double bond o attached to an o h group on the left side of the molecule there's a ch3 and then on the right there's a carboxyl group which contains the c double bond o and the oh this carboxyl group gets represented in condensed structural formulas in a couple of different ways one option is to write c o to h the other common option is to write c-o-o-h and you'll see these used interchangeably they mean the same thing the last example i'm going to go over is an aldehyde an aldehyde has a formal group which is c double bond o h and this has to be represented in a particular way in condensed structural formulas to distinguish it from an alcohol as we've done before we'll start on the left side of the molecule with ch3 then we'll move on to the formal group represent this group by drawing c-h-o it's important that the order be c-h-o and not c-o-h because o-h implies that there's an alcohol functional group which wouldn't be correct in this case this concludes this video on condensed structural formulas check out my other video on skeletal structures if you want to learn another way to represent organic molecules in a condensed format if you found this video useful check out the next one in the series or watch the prior video and consider subscribing to my youtube channel my name is brent kadrowski thanks for watching