Drawing Enantiomers the Easy Way Howard E. Dunn University of Southern Indiana, 8600 University Boulevard, Evansville, IN 47712
I t is not unusual for a student or a professor t o have difficulty drawing enantiomers (non-superimposable mirror image isomers). Most people draw one enantiomer and a straight line that represents a mirror. The mirror image is then drawn on the other side of the "mirror," usually with a great deal of effort. I have observed that i t is natural for your left hand to move in a fashion that isa mirror image of the motion of your right hand. Imagine that you are a conductor directing an orchestra. If you wave your hands as if you are directing the orchestra, you will notice that the movements of your left arm and hand are a mirror image of those of your right arm and hand. Now put a piece of chalk in each hand and transpose your arm and hand movements onto a chalk hoard. You have now drawn near perfect mirror images of a scribble, a fact that is enhanced when a vertical line is drawn between the two figures representing a mirror oriented perpendicular to the chalk board (Fig. 1). Try drawing era-2-chlorohicyclo[2.2.l.]heptaneand its mirror image. Put a piece of chalk in each hand and touch the chalk hoard. If you are right-handed, concentrate on drawing the bicyclic system with the right hand. The left hand will automatically draw a mirror image in synchronous but opposite motion of your right hand. When you have
finished drawing the bicyclic system, put in chlorine using your right hand for both figures. (If you do not do this, your left hand will draw in the chlorine backwards (mirror image) and it is hard to read.) Complete the diagram with a straight line for the mirror (Fig. 2). Now practice drawing a bicyclo[l.l.O.]butane system (Fig. 3). I have been teaching organic chemistry for a numher of years and have always had some degree ofhifficulty drawing enantiomeric structures of bicyclic systems. When I discovered this interesting techniaue of usine both hands simultaneously, I was ableto drawihese types of structures on the first attempt with absolutelv no difficultv. I have since found uut that this ability is nut unique to me.'rhe employment of this technique hns greatly facilitated mv teachine of stereochemistry. 1t should work equally well for the re&er.
Figure 2. ex+2-Chlwobicyclo[2.2.1.]heptanee
Figure 1. Scribbling with the len and right hand simultaneously
1042
Journal of Chemical Education
Figure 3. A bicyclo[l.l.O.]butans ring system.
