Drawing Newman Projections - Online Tutor, Practice Problems & Exam Prep

To analyze a condensed structure, convert it to a bond line structure, focusing on the bond of interest, such as C2-C3. Visualize the bond using a Newman projection, adding implied hydrogens only around the bond of interest. Draw the front and back carbons with their respective groups, ensuring to identify the most stable conformation, typically the anti conformation with a dihedral angle of 180 degrees. This method aids in understanding conformational analysis and stability in organic compounds.

Introduction to Drawing Newman Projections

Now that we understand the differences in energy between the different rotations of a Newman Projection, I want to really go in-depth on how to draw and interpret a Newman Projection. Alright? So there is a method to the madness and it's just a series of steps that I want to teach you. Alright? So let's say that you have the following example. This is a very common problem that you could see on your exam. Draw the most energetically favorable Newman Projection for that 5 carbon chain down the C₂, C₃ bond. Okay? So how do we even begin to approach this? We need to use steps.

Step 1 to Drawing Newman Projections

The first thing that I always do is, if you're given a condensed structure, which is often the case, you need to convert the problem into a bond-line structure. Okay? So what that means is that I want to take this 5 Carbon chain, or whatever I'm given, and turn it into bond line. So that's the first thing I'm going to do. Five carbons right there. So, this is pentane.

Step 2 to Drawing Newman Projections

The second thing I'm going to do is I'm going to highlight the bond of interest. What is the bond of interest? What? It's this, C₂C₃. That's your professor telling you that he wants you to focus on a certain bond that's going to rotate. Okay? Just like when I was talking to you about conformers that you could have sigma with S cis or S trans, he's picking out which sigma bond you're going to use, which sigma bond you're going to rotate. That's going to be this sigma bond right there. Because basically, what you want to do is you want to go from the second carbon to the third carbon. That's what C₂C₃ means. C₂C₃. Alright? Now, it could have also been this one, just letting you know, it could have also been this one because if you were counting your one from over here, then this would have been your 2 and your 3. Okay? But I'll just go ahead and use this other one. So this is my 2, this is my 3. Perfect. So, I highlighted the bond of interest. You don't need to necessarily write the numbers as long as you just know which bond it is.

Step 3 to Drawing Newman Projections

What we want to do is, this part sounds silly, I'm going to redraw this, but I actually want you to do the eyeball thing. I want you to draw an eyeball looking down the length of that bond. Okay? So, I want you to draw an eyeball and make it look straight at that carbon. Okay, so pretend that's you, squinting your eyes at it and you're going to try to figure out what this thing is going to look like if I was looking straight at it.

Step 4 to Drawing Newman Projections

Now the way you're going to do that is that you surround only the bond of interest with all implied hydrogens. That means if there's any implied hydrogens on that carbon or on that carbon, I need to add them. Okay? How about the hydrogens on that carbon? Do I add those as well? No, because that's not the bond of interest. The bond of interest is only going to be from 2 to 3. So what that means is I'm going to add 2 H's here and I'm also going to add 2 H's here. Okay? But I'm not going to add H's anywhere else because that's not the bond of interest.

Step 5 to Drawing Newman Projections

Now what we're going to do is we're going to draw a front carbon with 3 groups in the front and then a back carbon with 3 groups in the back like I was doing when I told you guys about the way the Newman Projection works. So I'm going to say that, for example, little dot. Okay little dot. Okay? And I would draw that it has 3 things coming off of it. Okay? You can draw your little triangle thing or whatever that's called, however you want. You can start with it with a point up or you can start with a point down. It doesn't matter as long as the other one is consistent. So basically, what I would say is then, okay, what are the three things that that red carbon is attached to? Well, it seems to be attached to an H on the top, an H on the top, and then a CH₃ at the bottom. That is this CH₃ right here. Get that? Then I look back at the blue one. The blue one, imagine that it's kind of peeking out from behind the red one. So the blue one is going to be a circle behind and then I'm going to draw the 3 groups that the blue one has. So the blue one has what? It seems to have 2 H's, H and H. And then what else does it have? Well, it has a 2 carbon chain coming off of it. So that would be what you could just write as CH₂CH₃. Does that make sense? Okay? Another way to write that would have been to write ET, which stands for Ethyl. Okay? Another way to write CH₃ would be to write ME, which stands for Methyl. Okay? And there are abbreviations for a bunch of these different ones. Alright. And your professor might use those more than he actually uses the letters.

Step 6 to Drawing Newman Projections

So now that we've drawn that Newman projection, that is a valid Newman projection. That could be right. The only thing is that I don't know if it's the energy state that the professor was asking for because the professor could ask for any energy state. He could ask for anti. He could ask for gauche. He could ask for eclipse. Maybe even something in the middle. So I have to make sure that this is the exact one that he wants. Okay? So then to determine which dihedral angle would correspond, I have to go up here and see what he said. Well, he specifically said to draw the most energetically favorable. What does energetically stable mean? Stable. Okay? So we're looking for the most stable conformation. What is the most stable conformation? That's going to be anti. Remember, anti is the most stable. So let's go down and see if that's what I drew. And what's the bond dihedral angle, by the way, for anti? 180°. Let's go down and see if that's what I drew. What I have is a large group in the back and a large group in the front. They appear to be 180° degrees away from each other, so this would be anti. So this would be your right answer, and this would be what would get you the points on the exam. Okay? So even if I drew the wrong conformation at the beginning, you could still rotate it into the right conformation. The important part is that you're following all of these steps.

Draw the most energetic Newman Projection of CH₃CH(C₆H₅)CH₃

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Draw the most stable Newman Projection of CH₃CH₂ CH₂OH through the C2 – C1 bond. 

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Here’s what students ask on this topic:

How do you convert a condensed structure to a bond line structure for Newman projections?

To convert a condensed structure to a bond line structure, follow these steps: Identify the carbon chain and draw it as a zigzag line, where each vertex represents a carbon atom. Add any substituents or functional groups to the appropriate carbons. For example, a condensed structure like CH₃CH₂CH₂CH₃ would be drawn as a four-carbon zigzag line. This conversion helps in visualizing the molecule more clearly for Newman projections.

What is the bond of interest in a Newman projection and how do you identify it?

The bond of interest in a Newman projection is the specific sigma bond you are analyzing for rotation. To identify it, look for the bond specified in the problem, often denoted by the carbons it connects, such as C2-C3. Highlight this bond in your bond line structure, as it will be the axis around which you visualize the molecule in the Newman projection.

How do you draw the front and back carbons in a Newman projection?

In a Newman projection, the front carbon is represented by a dot, and the back carbon is represented by a circle. From the dot, draw three lines representing the bonds to the front carbon's substituents. From the circle, draw three lines representing the bonds to the back carbon's substituents. Ensure the groups are positioned correctly to reflect the molecule's 3D structure.

What is the most stable conformation in a Newman projection and how do you identify it?

The most stable conformation in a Newman projection is typically the anti conformation, where the largest groups on the front and back carbons are 180 degrees apart. This minimizes steric hindrance. To identify it, look for a dihedral angle of 180 degrees between the largest groups. This conformation is energetically favorable due to reduced repulsion between bulky groups.

How do you determine the dihedral angle in a Newman projection?

The dihedral angle in a Newman projection is the angle between two substituents on adjacent carbons. To determine it, visualize the molecule from the perspective of the bond of interest. Measure the angle between the substituents on the front and back carbons. Common angles are 0 degrees (eclipsed), 60 degrees (gauche), and 180 degrees (anti).