Handedness of molecules

There are many other examples of interrelationship. Symmetry, for example, is of fundamental importance in the sciences and arts alike. It plays a key role in our understanding of the atomic world as well as the cosmos. The handedness of molecules, with nature selecting one... 

In Chapter 5 we examine the handedness of molecules, and ask. How important is the three-dimensional shape of a molecule ... 

In summary, the usual prescriptions of statistical quantum mechanics cannot explain chemical phenomena such as isomerism or the handedness of molecules. The question is then how to introduce effective thermal states for different isomers or differently handed molecules, etc. 

Thomson (Lord Kelvin) coined a word for this property. He defined an object as chiral if it is not superposable on its mirror image. Applying Thomson s term to chemistry, we say that a molecule is chiral if its two mirror-image forms are not superposable in three dimensions. The work chiral is derived from the Greek word cheir, meaning hand, and it is entirely appropriate to speak of the handedness of molecules. The opposite of chiral is achiral. A molecule that is superposable on its mirror image is achiral. 

Nowadays we are in the fortunate position of being able to carry out X-ray crystallography on crystalline derivatives of optically active terpenoids. This enables us to see the actual handedness of molecules. In the early days of stereochemistry, this was not possible and absolute stereochemistry could only be determined relative to a standard. Since the initial work on stereochemistry was carried out on sugars and their... 

There is a language problem introduced by the choice of the Greek word chiral to describe the phenomenon of handedness of molecules. In Greek, the word for not chiral is achiral. This poses no problem in Greek, but, at least in spoken English it does. It is often difficult to distinguish between Compound X is a chiral molecule and Compound X is achiral. ... 

This chapter deals almost exclusively with the concept and consequences of the handedness of molecules—chirality. Some molecules are related to each other as are your left and right hands. These are nonsuperimposahle mirror images, or enantiomers. 

---