Flip and Rotate Molecules

Introduction:

When finding the relationship between two molecules, one of the most difficult decisions is whether two molecules are the same or different.  Often the two molecules will be shown in different orientations.  Therefore, to compare the two molecules, it is helpful to change the orientation of one of the molecules by rotating it and/or flipping it.  You can do this by making a model, but it is faster to learn how do this without making a model.

How to:

Rotating.  When rotating a molecule in the plane of the page, the up and down groups should remain the same.  In both examples below, the OH group points up and will stay pointing up after rotation.

Hint:  You can rotate the paper to check that the two molecules that you have drawn are the same.  Make sure the the position (left and right) of the groups did not get switched.

Flipping.  When flipping the molecule, up and down groups will all be reversed.  In both examples below, the OH group switches from up to down after being flipped.

Examples:

Comment:  Do not worry about whether the rotation is 30° or 120° or that the flip is horizontal or vertical.  The point of this exercise is to be able to manipulate the molecules so that you can convince yourself that all the molecules are the same molecules.