Identifying chirality.

•	How can we predict whether or not a molecule is chiral?

•	A molecule can’t be chiral if it contains a plane of symmetry. If a molecule has a plane of symmetry then it will be superimposable on its mirror image and will be achiral.

•	Any molecule containing a carbon atom carrying four different groups will not have a plane of symmetry and must therefore be chiral. Such carbon atoms are know as stereogenic or chiral centers.

•	All amino acids have a carbon carrying an amino group, a carboxyl group, a hydrogen atom and an R group (for alanine R=methyl). Therefore, all amino acids (except for glycine where R=H, see refcode GLYCIN) are chiral.

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Natural alanine, extracted from plants, consists of one enantiomer only. Samples of chiral molecules that contain only one enantiomer are called enantiomerically pure. However, alanine produced in the lab from achiral starting materials will be a 50:50 mixture of enantiomers and is referred to as being racemic. In fact, nearly all chiral molecules in living systems are found as single enantiomers not as racemic mixtures.

•	Examine each of the following structures and determine whether or not they are chiral.

•	Toluene (refcode: TOLUEN)

•	Lactic acid (refcode: YILLAG)

•	Citric acid (refcode: CITARC)

•	2,2,2-Trifluoro-1-(9-anthryl)ethanol (refcode: SOCLIF)