Figure 2.7. Axial and Equatorial Positions in Cyclohexane
During a chair flip, axial components become equatorial and vice-versa. However, components
pointing “up” (wedge) remain up and components pointing “down” (dash) remain down.In rings with more than one substituent, the preferred chair form is determined by the larger group,
which will prefer the equatorial position. These rings also have associated nomenclature. If both
groups are located on the same side of the ring, the molecule is called cis; if they are on opposite
sides of the ring, it is called trans, as shown in Figure 2.8. These same terms are used for molecules
with double bonds, as explained later in this chapter.
Figure 2.8. Nomenclature of Rings with Multiple SubstituentsCONFIGURATIONAL ISOMERS
Unlike conformational isomers that interconvert by simple bond rotation, configurational isomers
can only change from one form to another by breaking and reforming covalent bonds. The two
categories of configurational isomers are enantiomers and diastereomers. Both enantiomers and
diastereomers can also be considered optical isomers because the different spatial arrangement of
groups in these molecules affects the rotation of plane-polarized light.
Chirality
An object is considered chiral if its mirror image cannot be superimposed on the original object; this
implies that the molecule lacks an internal plane of symmetry. Chirality can also be thought of as