Condensed Structural Formula: Study with Video Lessons, Practice Problems & Examples

The condensed structure is a textual representation of organic molecules, allowing chemists to convey connectivity without drawings. It uses parentheses to indicate repeating units, such as CH₂(n), and branches, where a carbon atom must have four bonds. Understanding these representations is crucial for interconverting between bond line and condensed structures, as both formats may appear in assessments. Mastery of this concept aids in visualizing molecular architecture and ensures accurate interpretation of complex organic compounds.

How to interpret condensed structures.

Hey guys. So now we're going to talk about another way to represent organic structures and that's called the condensed structure. The condensed method is a common way to describe the connectivity. Connectivity, how a molecule is connected. So my speculation is that the logic behind this is that professors and chemists wanted a way to represent these molecules using only a text editor. Back in the day, there weren't these fancy drawing programs. In fact, all they had were typewriters. Right? And they wanted some way to be able to notate what a molecule looked like without having to draw fancy structures. Alright? And that's where they came upon the condensed structure. Now one thing that's important for this class is that you're going to have to really learn how to interconvert between bond line and condensed very quickly. The reason is because your professor, just to trick you, will use both structures interchangeably. One question might be in bond line, another question might be in condensed. And typically, just from my years of tutoring experience, I know that students really don't like to think in condensed structure because it's kind of tricky. So what I'm going to do today is I'm going to really show you, okay, how to interpret it. So let's go ahead and look at there are two different types. Let's start off with the full condensed structure. The full condensed structure is literally only text. And as you can see, we're taking a bond line structure and we're going to represent it in just only one line of text. Now, a lot of this is straightforward, meaning that you can see that this first CH₃ here is represented by that CH₃ there. Okay? So then you would think, oh, this isn't so bad. The confusing part is that parentheses can be used to represent different things depending on the subscript in front of them. So let's go ahead and look at that. The first interesting parenthesis that you should know is this one that I've indicated in blue, which is a CH₂⁺ subscript. Okay? So notice that I have CH₂(3). What that means is that I have a repeating unit that's going to happen over and over and over again. So when I have CH₂ with a 3, that doesn't mean I have three CH₂s sticking out of one place. What it means is I have three CH₂'s attached in order, like in a line. Does that make sense so far? The reason that saves us a lot of time is because some of these molecules can get really, really long. Imagine having a molecule that's a 100 carbons long. Do you want to write a 100 CH₂'s? No. It's way easier just to put CH₂ in parentheses with a 100 underneath it. And that means I'm going to repeat this unit 100 times. Cool so far? Awesome. So let's keep going. Then we have this red one. The red one is parentheses alone. If you have parentheses alone, that indicates that you have a branch coming off of the chain. Alright? Now what's going to be interesting here is that sometimes these parentheses are optional, meaning that your professor may not always be so nice as to put those parentheses there to say that there's a branch. Sometimes you're just going to have to know, alright, let's look at the logic here. I have a carbon right here and that carbon is attached to two other things. It's attached to one half of the chain on the left and one half of the chain on the right. Right? By the way, this carbon, let's go ahead and locate it. It's this one right here. Okay? So let's just make sure that we know what we're talking about. Okay? So that carbon has a part of the chain on the left and a part of the chain on the right. Okay? But it also has supposed to have two other things coming off of it because remember carbon wants to have four bonds. Right? So what are those two other things? Well, there's an H, that means that I have one H sticking off there. Okay? And I also have an OH. Now notice that in this case I was nice and I put it in parentheses. What that meant was that it's very easy to say, oh, the OH is the thing that's coming off here. Done. I have my four bonds. Perfect. But sometimes you might see it as just CHOH. And then what you would need to know is that, okay, one of them, the H is going in one direction, the OH is going in the other, but you know that both of them are attached to that carbon because remember that carbon needs 4 bonds. That's kind of the way that we think about it. You always think in terms of how can I make carbon have 4 bonds? Finally, as you can see, there's one more type of parenthesis. Sorry about getting a little sidetracked, but I want you guys to see an example of that. And then the last one is that if I have something else that's in parentheses other than CH₂ and has a number in front of it. So in this case, I'm giving you CH₃ with a 2 in the magenta brackets. Okay? And what that means is that these things are not attached in a line, they're both attached to the same carbon. Okay? So basically the only time that I have things in a line repeating is if it's CH₂. That would mean that it would be linear. So go ahead and write that down. Linear meaning that it's all in one line. But if I have 2 things that are not CH₃ or 3, like here, these would indicate branching. Okay? Because of the fact that both of these CH₃s must be coming off of 1 carbon and what that would be is that they would be attached to this one right here. Okay? Now let's look at the logic with this one. So let's look at this carbon. Where is that carbon? That carbon is right here. Okay? So that carbon needs to have four things attached to it. Right? Well, first of all, it has the whole left part of the chain. Easy. And then it has, let's look at it. Let's see what's after the carbon. After the carbon, I have an H and I have a CH₂, I mean, and I have a CH carbon, I have an H and I have a CH₂, I mean, and I have a CH₃ and then I have another CH₃ because it says 2. Those are the three other things that are attached to that carbon. So this would be bond 2, bond 3 and bond attached to that carbon. So this would be bond 2, bond 3 and bond 4. And if we were to go ahead and draw that, you would see that I have an H here and then I have CH₃ here and then I have CH₃ here. Do you get that? At the end of the day, the carbon still has 4 bonds, so it's fine. But if you ever draw a structure, if you ever translate a structure that does not give carbon 4 bonds, then you know you made a mistake.

How to draw condensed mixed structures.

Alright. So now let's look at one that's a little bit easier, and that's the condensed mix structure. The condensed mix structure is one in which I have a ring. So I'm just going to put here "rings". Okay? The reason is because rings are very, very difficult. If you think about it, rings would be very difficult to draw in a text because a ring could be a certain shape, it's 2-dimensional, and most text editors don't give you the ability to draw up and across. It's only to go across. Think that you're on a typewriter. Would you be able to type a ring? No. So what you do with the condensed mixed structure is that the ring is the only thing that stays this bond line, and then everything else that's branching off of it goes to condensed. So, as you can see, what I do is I take this thing, convert it over here, and now all of the branches coming off of the ring become a condensed formula. Does that make sense so far? Cool.

I also wanted to talk about a few other things right here. Notice that with this, let's start off with this one because it's kind of easy. Okay? What I have is think about it. I have parenthesis that has, does it have CH₂ in parenthesis? No. It's something other than CH₂. Right? It's actually CH₃. So that must mean what? Does it mean that all the CH₃'s are in a line? No. That would only be if it was CH₂. What it means is that all 3 CH₃'s are coming off of the same carbon. Does that make sense? And that's what we see right here. I have carbon and then CH₃ CH₃ CH₃. Does that make sense? Cool. I hope so.

Now let's go to one that's a little bit trickier. That is this one over on the left-hand side. So now what is this weird line that I drew? Like where did that come from? This line is a pretend line. Okay? So don't pay too much attention to it. All I'm trying to do is separate the right side from the left side to show you how we draw it differently. Okay? Now because condensed structure has to do with connection, it has to do with what is connected to what, when you're on the left-hand side of a mixed structure, you always have to draw in reverse. You have put the letters backwards. Okay? The reason is because I have to show exactly what order they're connected in. So let's look at this. This right here is an O attached to a CH₃. Would you agree with that? Cool. But if I just write if I, instead of writing this, let's say that I wrote O CH₃ like that. Would that be correct? That would actually be incorrect. So go ahead and put an X on that. K? That would be wrong. The reason is because it looks like the O is attached to one of the H's. Right? That doesn't make a lot of sense. So the way we need to show this is that the O is actually connected to the carbon first, and the carbon is connected to 3 H's. Right? So then the way that we draw it is O, C, and then H₃ after that. Does that make sense? This only applies when you're on the left side. Because if you're on the right side, then it just makes sense the way it naturally is. You would just write it out according to the connectivity. The left side is the part that gets a little bit tricky.

Now, some of you guys might be asking this question, Johnny, but what if it's the top or at the bottom? Because that's not really how about if it's in between? So how about if I had a line right here and I wanted to put text there? Well, if it's right in the middle, then obviously go to the right because I can just do CH₃O or whatever. Or I could do, in this case, it would be O CH₃ if it had been there. Okay? So obviously what I'm trying to say is that you would only go to the left, you would only reverse it if you absolutely have to because it's on the left-hand side. Does that make sense? But if it's at the top or the bottom, just go to the right like normal because there's plenty of room to draw it. Okay?

So, let's go to the last example, which is this one down here that has a double bond to carbon and to oxygen. That's this thing right there. Okay? This is a situation where if you have a double bond, many times your professor is going to put an equal sign there. An equal sign represents a double bond, which is pretty easy. If it was a triple bond, then they would put one of the equal signs that has 3 bars. Bars. K? But sometimes your professors will be really tricky, and they will just write this like C=OCH₃ and they will skip the equal sign. That's tricky. Right? How are you supposed to know that that is a double bond without being told that it's a double bond? Can you guys think about it? Is there any way to know? The answer is it goes back to carbon having 4 bonds. Okay? If this is a carbon and an oxygen, and if that carbon needs 4 bonds, then what that means is that this carbon must be attached to that oxygen with a double bond. The reason is because I have a bond on the left, I have a bond on the right, and then I must have 2 bonds that are missing. Those 2 bonds that are missing are the ones that are attached to the O that makes it a double bond right there. Does that kind of make sense? Now, like I was saying, most professors are going to be nice, and they're going to give you that double bond. But I'm just trying to show you just in case your professor decides to be a tool and not put that in there so that you guys will know that you can actually calculate it based on carbon having 4 bonds. Okay? So I'm going to give you plenty of practice. Don't worry.

Convert the condensed structure into a bondline structure 

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Here’s what students ask on this topic:

What is a condensed structural formula in organic chemistry?

A condensed structural formula is a way to represent the connectivity of atoms in an organic molecule using text. It simplifies the depiction of molecules by omitting some or all of the bonds and grouping atoms together. For example, instead of drawing out each bond, a molecule like ethane (C₂H₆) can be written as CH₃CH₃. Parentheses are used to indicate repeating units or branches, such as CH₃(CH₂)₃CH₃ for pentane. This method is particularly useful for long molecules and helps in quickly visualizing the structure without detailed drawings.

How do you convert a bond-line structure to a condensed structural formula?

To convert a bond-line structure to a condensed structural formula, follow these steps: 1) Identify all carbon atoms and their attached hydrogen atoms. 2) Write each carbon atom followed by its attached hydrogen atoms (e.g., CH₃, CH₂). 3) Use parentheses to indicate repeating units or branches. For example, a bond-line structure of butane can be converted to CH₃CH₂CH₂CH₃. For more complex structures, ensure each carbon has four bonds by including other attached groups or atoms.

What do parentheses mean in a condensed structural formula?

In a condensed structural formula, parentheses serve two main purposes: 1) Indicating repeating units: For example, CH₂(CH₂)₃CH₃ means three CH₂ groups are repeated in a chain. 2) Indicating branches: For example, CH₃CH(CH₃)CH₃ shows a CH₃ group branching off the main chain. These conventions help simplify the representation of complex molecules and ensure clarity in the structure's connectivity.

Why is it important to learn how to interconvert between bond-line and condensed structures?

Learning to interconvert between bond-line and condensed structures is crucial because both formats are commonly used in organic chemistry. Professors may use them interchangeably in exams and assignments to test your understanding. Mastery of this skill ensures you can accurately interpret and visualize molecular structures, which is essential for solving problems related to reactivity, synthesis, and molecular properties. It also helps in communicating chemical information effectively in both academic and professional settings.

How do you represent a branched molecule in a condensed structural formula?

To represent a branched molecule in a condensed structural formula, use parentheses to indicate the branches. For example, isobutane, which has a central carbon with three CH₃ groups attached, can be written as (CH₃)₃C. Each group in parentheses is attached to the carbon atom outside the parentheses. Ensure that each carbon atom has four bonds by including all attached groups or atoms. This method simplifies the depiction of complex branched structures.