Concepts Explained

September 26, 2019
Teaching & LearningGianna Manchester

Throughout college, both when I was a student and a tutor for organic chemistry, I carried a model set in my backpack.  The bulkiness and the clinking of the atoms drove me crazy, but it was the only way I could complete my homework and effectively explain concepts to students.  If only ModelAR existed then….

The ModelAR app is an alternative to a traditional model set and it comes with its perks: no bulkiness, no clinking, it’s always on you (on your phone), and, the best part, it’s free! 

Here I am going to show you how ModelAR can be used to help you on your homework with specific topics including stereochemistry, Newman projections, and chair conformations. 

Note: When constructing molecules in ModelAR from your homework, it is important to recognize that wedges signify the substituent coming out of the plane and dashes signify the substituent going into the plane. Once you understand that part, building molecules in ModelAR is simple! Let’s take a look at these examples to see how ModelAR can help you with your homework.*

Stereochemistry

ModelAR is useful for determining stereochemistry because you can rotate the molecule around a selected atom and rotate single bonds to view the molecule in a way that allows you to answer the question.  It is also helpful to learn how to “see in 3D” and get accustomed to understanding how wedges and dashes translate to a 3-dimensional structure. 

  1. Determine whether the following compounds are cis or trans, E or Z, and R or S. Assign appropriate configuration(s) to each of the following. If there is more than one type of stereocenter, give labels for each. If no labels apply, write “none” in the box. (No partial credit.)   (Answers given below.)


A.


B.



C.



Newman Projections

When thinking about Newman Projections in ModelAR, you can rotate the molecule to look down a certain bond by selecting an atom to rotate around, then swipe outside of the molecule. To rotate the bond, rotate the molecule until the bond is visible, then tap the bond to select it, and swipe to rotate before rotating the molecule again to look down the bond. 

2.  Draw Newman Projections of the most stable conformation and a gauche conformation of 2-methylbutane.

Chair Conformations

Understanding chair conformations is a difficult topic for students, especially in regards to knowing which hydrogens are up or down and axial or equatorial.  ModelAR can be used to explore the conformations of cyclohexane and the orientation of its substituents.

3. Draw the chair conformation of the following molecule 




*These problems were taken from a Chemistry 210: Structure and Reactivity Course Pack from the University of Michigan, Academic year 2006-2007. 


Answers:

A.



B.

C.


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