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.
Drawing Newman Projections - Online Tutor, Practice Problems & Exam Prep
As we learned already, we use Newman projections to visualize the rotations of conformers. Now we will learn the steps involved to draw the perfect one.
Introduction to Drawing Newman Projections
Video transcript
Six Steps to Drawing Newman Projections
Worked Example:Draw the most energetically favorable Newman Projection for CH3CH2CH2CH2CH3 down the C2 – C3 bond.
1. Convert problem into bondline structure
Step 1 to Drawing Newman Projections
Video transcript
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.
2. Highlight the bond of interest
Step 2 to Drawing Newman Projections
Video transcript
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.
3. Draw an eyeball glaring down the length of the bond
Step 3 to Drawing Newman Projections
Video transcript
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.
4. Surround only the bond of interest with ALL implied hydrogens
Step 4 to Drawing Newman Projections
Video transcript
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.
5. Draw a front carbon with 3 groups in the front and a back carbon with 3 groups in the back
Step 5 to Drawing Newman Projections
Video transcript
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.
6. Determine which dihedral angle would correspond
Step 6 to Drawing Newman Projections
Video transcript
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.
Hint:This question asked for the most energetically favorable = most stable. Which conformation is most stable?
The right answer was anti. You got it. So it turns out this time we drew it correctly on the first try. But there will be other examples where we will have to rotate the Newman Projection into the correct position.
Draw the most energetic Newman Projection of CH3CH(C6H5)CH3
Hint:Not all Newman Projections can form an anti, gauche and eclipsed conformation. If you have no clear large group on one side of the projection, you’ll just be stuck with projections called staggered (not overlapping) and eclipsed (overlapping).
Draw the most stable Newman Projection of CH3CH2 CH2OH through the C2 – C1 bond.
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