Bond Line Notation to Newman Projection

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5 3 b Fischer Projections

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Key Questions

  • A bond-line notation gives no stereochemical information, but here's how to convert a wedge-dash notation to a Newman projection.

    PROBLEM

    Convert the following wedge-dash structure of 2-chloro-3-methylpentane to a Newman projection through the C2-C3 bond.

    www.chemeddl.org

    Step 1. Draw two Newman projection templates.

    enter image source here

    • Draw two circles.
    • Put a dot in the centre of each. These represent C-2. C-3 is hiding behind the circles.
    • On one circle, draw a Y with the spokes radiating from the dot at 120° angles. On the other circle, draw an inverted Y. These represent the bonds from C-2.
    • Draw lines coming off each circle that bisect the angles of the Y. These represent the bonds from C-3.

    You will choose one of these templates as the basis for your projection.

    Step 2. View the molecule along the C2-C3 axis with your eye closest to C2.

    Your eye will be at the lower left of the image.

    The closest bonds make an inverted Y, so you will choose the second template for your projection.

    Step 3. Place the groups onto your template.

    • The groups on C-2 go on the front carbon, The groups on C-3 go on the back carbon.
    • The "normal" groups go on the vertical lines: CH₃ in front; CH₂CH₃ behind.
    • The wedged groups go on the right hand side: H in front; CH₃ in back.
    • The dashed groups go on the left hand side: Cl in front; H in back.

    www.chemeddl.org

    And you have your Newman projection.

  • When you want to answer questions about the most stable Newman conformation or just want to make the molecule look more complicated.

    Newman projections are a fascinating way to look at a molecule. You essentially are getting down to the level of the atoms themselves, as if you could be a tiny little person looking down one bond at a time. Imagine being this small, looking at the front carbon and NOT being able to see the bond behind it to the back carbon. Let's take ethane. Ethane only has two carbon atoms and three Hydrogen atoms bonded to each carbon. If you could be so small that when you look down the C-C bond and only see a carbon at front and at back, you would be a superhero: "TINY MAN". Unfortunately, the convention is to write the front carbon as a DOT and the back one as FAT CIRCLE, which makes no sense considering prospective drawings, but that's okay. We want you to see the back carbon so we pretend that back carbon would be bigger despite being farther from you.

    But I digress.

    You can then place the Hydrogens in 120 angles from each on the front carbon, then do the same for the Hydrogens at the back "fat" carbon. If the Hydrogens happen to overlap in what we call the "eclipsed" conformation, that's bad for stability. The molecule has high energy which in ochem is BAD. If you then rotate either the back or front carbon 60 degrees, you will click into the awesome conformation called "staggered", lower energy which is GOOD in ochem.

    Basically, Newman conformations give a straight shot view of a bond down the axis of the bond, as if you were TINY MAN. It is not as easy to read the drawing as simple bond line drawings but it's a great way to determine stability of a molecule and great questions for professors to ask to lower the curve.

  • Answer:

    You convert the bond-line structure to a wedge-dash structure. Then you convert the wedge-dash structure to a Newman projection.

    Explanation:

    The bond line structure of ethane is

    enter image source here

    The wedge-dash structures for the staggered and eclipsed conformations are:

    www.ch.ic.ac.uk

    Here's how to convert the wedge-dash structures to Newman Projections.

    Staggered Ethane

    Step 1. View the molecule along the C1-C2 axis with your eye at the left-hand end.

    The closest bonds make an inverted Y, so you will choose that template for your projection.

    Step 2. Place the groups onto your template.

    All groups on the carbon atoms are H atoms.

    science.uvu.edu

    And you have your staggered Newman projection for ethane.

    Eclipsed Ethane

    Step 1. Draw two eclipsed Newman templates.

    enter image source here

    Step 2. View the molecule along the C1-C2 axis with your eye at the left-hand end.

    The closest bonds make an inverted Y, so you will choose the second template for your projection.

    Step 3. Place the groups onto your template.

    All groups on the carbon atoms are H atoms.

    enter image source here

    And you have your eclipsed Newman projection for ethane.

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