Meso Tetramer of Lactic Acid Mimicking Nonactin

To simplify the nonactin problem, let's look at a simpler model -- a tetramer of lactic acid constructed in the same fashion as nonactin but with a single chiral center in each lactic acid unit (magenta oval, fig. 1). The mirror image of fig. 1 is seen as fig. 2. If fig. 2 can be rotated about an axis system and be superimposed upon fig.1, then fig. 1 and fig. 2 are not chiral, superimposable mirror images. Rotation of fig. 2 by 180^o about the z-axis gives fig. 3. Although the methyl groups superimpose, the CO₂ units point in opposite directions. Now rotate fig. 3 90^o about the y-axis in a clockwise direction. Fig. 1 and fig. 4 are identical! Therefore, fig. 1 and fig. 2, although mirror images, are indeed superimposable upon one another.