I see a lot of students who have trouble visualizing how molecules appear from different directions. Probably the best way to solve this problem is to buy and practice with a model kit, which really helps to make structures more concrete. However, as much as people like me nag their students to buy (and use) their model kits, inevitably there will be holdouts who just can’t be bothered. If you’re one of those people, today I will hold off on yet another finger-wagging diatribe in order to show you a technique you can use that will help to do some of the same things a model kit does, without actually having to use a model kit. Instead, you’re going to use your hands.
Let’s say you’re given this problem: pretty typical for an Org 1 midterm.
While the silence of the exam hall is punctuated by the popping of a hundred little plastic model kits from the students around you, here’s what you can do instead.
Step 1: Number the chain and draw in the “hidden hydrogens” for C2 and C3.
You can also draw in a “line of sight” if this helps, since we’re supposed to look along C2-C3.
Step 2: Make the following shape with your hand. Left or right hand is OK.
Step 3: Identify the substituent on the near carbon (i.e. C2, as per the directions in the question) that is in the plane of the page. In this case it is the methyl group (C1).
Step 4: Now turn your hand so that you overlay your thumb with the substituent in the plane of the page. The finger closest to you should now be the wedged substituent, and the finger furthest away is the dashed substituent.
Now turn your hand so that your thumb is pointing toward you. You can label your fingers if you feel artistic.
This will be the front of your Newman.
Repeat, looking from the opposite side (C3-C2).
This will be the back of your Newman. Et voila, here’s the final result:
Note that you can also do this in reverse to go from a Newman to a wedge-dash diagram. Just make sure that the substituent your thumb is supposed to represent is pointing either straight up or straight down.