The World’s Cheapest Molecular Model Kit

by James

in Alkanes, Conformations, Organic Chem Study Tips, Organic Chemistry 1

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.

1-model

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.

2-model

You can also draw in a “line of sight” if this helps, since we’re supposed to look along C2-C3.

3-model

Step 2: Make the following shape with your hand. Left or right hand is OK.

4-hand1 copy

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).

5-model

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.

6-newman

Now turn your hand so that your thumb is pointing toward you. You can label your fingers if you feel artistic.

7-model

This will be the front of your Newman.

8-model

Repeat, looking from the opposite side (C3-C2).

9backend copy

This will be the back of your Newman. Et voila, here’s the final result:

10-model

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.

 

Related Posts:

{ 7 comments… read them below or add one }

Med School Odyssey

I think I came up with a similar system myself, since figuring it all out by building models can take some time. Though after some practice drawing Newman projections, I was eventually able to be able to draw simple ones in my head.

But, if I’m ever not really sure, I’ll build a model – I don’t know anyone that’s been foolish enough to try getting through organic chemistry without modeling kit though.

Reply

James

I agree that they’re indispensible if you really want to make sure of something. There are rare exceptions, but the students who are really committed buy and use their kits.

Reply

Mike

Shucks, I thought this was going to be a post on the creative use of marshmallows, gumdrops, and toothpicks.

Except I’m not sure today’s organic students know what a gumdrop is…

Reply

James

I’m sure someone who set up a booth selling Ju-jubes and toothpicks right before an ochem midterm would do a brisk business.

Reply

amy

what are the cons of using a homemade model kit w/ gumdrops & toothpicks?

Reply

James

I wouldn’t use it for cyclohexane chairs, but it would be fine for Newman projections.

Reply

Alanna

This was so helpful! We aren’t allowed to use our model kits for exams in my class and I was having a hard time picturing things. Thank you!!

Reply

Leave a Comment