Skeletal Structure: Study with Video Lessons, Practice Problems & Examples

The bond line method simplifies organic molecule drawings by implying carbon atoms at each corner of a zigzag pattern, adhering to the octet rule. Hydrogens and lone pairs on heteroatoms, which are non-carbon atoms like nitrogen and oxygen, are also implied unless specified by formal charges. This approach reduces redundancy in structural representations, allowing for clearer visualization of molecular structures. Understanding these conventions is crucial for interpreting and drawing organic compounds effectively.

How bondline is different from Lewis Structures.

So the bond line method is a way to simplify drawings of organic molecules based on the octet rule. As long as you have a good understanding of the octet rule, you should be fine. Like, you should be able to convert drawings into bond line representations easily. Alright? It turns out that in order to save time, we are going to be implying a lot of different types of information that you can derive from the octet rule. The first thing that we are going to do is remember that organic chemistry is the study of carbon and carbon structures. If we had to write out every single carbon, pardon my French, that would be ridiculous, right? What we want to do is figure out a way that we don't have to write 'C, C, C, C', like, a hundred times in a row. So, in bond line structures, carbons are implied. What that means is that every corner, where we have a zigzag pattern, is assumed to represent a carbon. I'm going to show you how that looks in a second. Another aspect of organic chemistry is the elimination of repetitive elements. There are a lot of hydrogens, okay? It turns out that hydrogens are also going to be implied. Why? Because it would be tedious to have to write all of them. If we are not drawing hydrogen, how do we know how many there are? All we have to do is use the octet rule. We said that every carbon is assumed to possess enough hydrogens to fill its octet. For example, if a carbon has 2 bonds to other carbons and we don't show any hydrogens, we have to add bonds there in order for that carbon to fulfill its octet. So think about it this way: Carbon wants to have eight electrons in its octet. If it only has 2 bonds to carbon, that means that there must be 2 bonds to hydrogen. That’s the way we think. We do a bit of mental subtraction, and that's the number of hydrogens that are going to be implied on that structure. What else is implied? Lone pairs, because lone pairs would be super repetitive too. Lone pairs are implied. What that means is that we are not going to draw all the lone pairs. We are just going to assume that heteroatoms will have enough lone pairs to fulfill their octet unless otherwise stated, unless there is a charge. By the way, I need to define something. What the heck is a heteroatom? I just mentioned it without explanation. A heteroatom is any atom that is different from carbon. So I am going to say it is a non-carbon atom. What that means is that nitrogen, oxygen, fluorine, all of those would be heteroatoms, and we are not going to draw a lone pair. We just assume that they have enough lone pairs to fulfill their octet unless otherwise stated, and what we use for that is formal charges. Now that we know how to do formal charges, formal charges are a huge part of the bond line structure. We never draw lone pairs; we only draw formal charges and use formal charges when an atom does not satisfy its bonding preferences. If there is a messed up bonding preference, we use a formal charge. We don't actually draw the lone pairs. There is one extra rule that you guys should be aware of: all hydrogens on heteroatoms must be drawn explicitly. Do you guys remember what a heteroatom was again? Non-carbon. So oxygen, nitrogen, whatever. All hydrogens on heteroatoms must be drawn explicitly. The reason is because it could get tricky if we just don't draw the lone pairs, and if we also don't draw the hydrogens on a heteroatom, then it would be unclear whether it has a hydrogen or a lone pair. So, in order to avoid that confusion, we actually are going to include all the hydrogens that are drawn directly on a heteroatom.

Conversion of ethanol from electron dot to bondline

So I wanted to show you guys this little diagram that I drew showing how we can go from one to the other. So the electron dot structure is like the most simple form of structure that we drew in general chemistry. Basically, what we had was that we drew out every electron explicitly and we would show that every single bond was made by the sharing of 2 electrons. Then when we convert it to Lewis structure, Lewis structure is also used in general chemistry. You should be aware of it. But Lewis structure was just a little bit different. The only difference is that instead of showing the dots being shared, it replaced dots with sticks. So what it did was anytime they had dots being shared, it replaced them with sticks and that was a Lewis structure. But notice that a Lewis structure is still kind of annoying because I have to draw every carbon, I have to draw every hydrogen and I have to draw every lone pair. So it's going to take me a long time to draw everything Lewis. So then we decide well, is there a faster way to do this? Well, bond line, look how fast that is to draw because I'm ignoring the carbons. I'm just saying that every corner represents a carbon. I'm ignoring all of the hydrogens attached to carbon because I'm just assuming that if this carbon has 2 bonds, that must mean that it has 2 hydrogens and if this carbon has one bond attached to it, then it must have 3 hydrogens. Then I'm implying the lone pairs. I'm not drawing them because I'm assuming that it has enough lone pairs to fulfill its octet. And then lastly, I am including that H because it would be confusing if I didn't include the H. All right. So that is the way bond line works and that's what we're going to do basically for the rest of this topic. We're just going to do a bunch of practice problems for this.

How many implied hydrogens does each labeled carbon have? 

• A. A=1; B=1; C=2
• B. A=3; B=2; C=3
• C. A=2; B=2; C=3
• D. A=1; B=1; C=3

How many implied hydrogens does each labeled carbon have? 

• A. A=1; B=2; C=0; D=0
• B. A=2; B=1; C=1; D=0
• C. A=1; B=0; C=0; D=2
• D. A=1; B=2; C=1; D=1

Convert the structure into a line-angle structure. Be sure to assign ALL necessary formal and net charges.

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Convert the structure into a line-angle structure. Be sure to assign ALL necessary formal and net charges.

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Convert the structure into a line-angle structure. Be sure to assign ALL necessary formal and net charges.

 

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Convert the structure into a line-angle structure. Be sure to assign ALL necessary formal and net charges.

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Here’s what students ask on this topic:

What is the bond line method in organic chemistry?

The bond line method is a simplified way to draw organic molecules. In this method, carbon atoms are implied at each corner or end of a zigzag line, and hydrogen atoms attached to carbons are also implied. This method adheres to the octet rule, meaning each carbon is assumed to have enough hydrogens to complete its octet. Lone pairs on heteroatoms (non-carbon atoms like nitrogen and oxygen) are also implied unless specified by formal charges. This approach reduces redundancy and makes it easier to visualize complex organic structures.

How do you determine the number of hydrogen atoms in a bond line structure?

In a bond line structure, hydrogen atoms attached to carbon are implied. To determine the number of hydrogens, use the octet rule. Each carbon wants 8 electrons in its valence shell. If a carbon has 2 bonds to other carbons, it needs 2 more bonds to hydrogens to complete its octet. For example, a carbon with 2 bonds to other carbons will have 2 implied hydrogens. This mental subtraction helps you figure out the number of hydrogens without drawing them explicitly.

What are heteroatoms in the context of bond line structures?

Heteroatoms are non-carbon atoms in an organic molecule, such as nitrogen, oxygen, and fluorine. In bond line structures, lone pairs on heteroatoms are implied to avoid redundancy. However, any hydrogen atoms attached to heteroatoms must be drawn explicitly to avoid confusion. Formal charges are used to indicate when an atom does not satisfy its typical bonding preferences, rather than drawing lone pairs.

Why are formal charges important in bond line structures?

Formal charges are crucial in bond line structures because they indicate when an atom does not satisfy its typical bonding preferences. Instead of drawing lone pairs, which can be repetitive, formal charges provide a clear way to show deviations from the expected number of bonds. This helps in accurately representing the electronic structure of the molecule and understanding its reactivity and properties.

How do you represent lone pairs in bond line structures?

In bond line structures, lone pairs on heteroatoms (non-carbon atoms like nitrogen and oxygen) are implied and not drawn explicitly. This is to reduce redundancy and simplify the drawing. However, if a formal charge is present, it indicates that the atom does not satisfy its typical bonding preferences, which indirectly informs about the presence of lone pairs. Hydrogen atoms attached to heteroatoms must be drawn explicitly to avoid confusion.