CHAPTER 15: Unit 1. Chirality: Structures & Nomenclature

Chirality: Structures & Nomenclature:

Molecules and their mirror images- looking glass symmetry:

Left and right hands are mirror images of each other, but they are not identical. In case of an organic molecule, if the carbon is attached to four different substituents then its’ mirror image is not superimposable on its mirror image is said to be chiral.

Other molecules are like socks. Two socks form a pair are mirror images that are superimposable.

PRACTICE PROBLEM:

Classify each object as chiral or achiral.

Chirality in nature:

On a macroscopic scale, many naturally occurring objects possess handedness. Examples include helical seashells shaped like right handed srews, and plants such as honeysuckle that wind in a left handed helix.

Chirality center: To locate the chirality center in a molecule, we have to examine each tetrahedral molecule and look at the four groups not the four atoms bonded to it. CBrClFI molecules has one chiral center because the carbon atom is bonded to four different groups. It is to be noted that a carbon atom bonded to two or more like groups is bever a chiral molecule. When carbon atom contains double bond, it doesn’t produce chiral atom because it is not connected to four different substituents.

Lager organic molecules can have two, three or even hundreds of chirality centers. In locating chirality centers in skeletal structures, carbon must have four bonds. For example, the following compound has a chiral center.

Chiral center can also be found in cyclic compounds. Often it is denoted by an asterisk sign.

A chiral molecule and its mirror images form a pair of enantiomers.