sm_logo.gif (1738 bytes) Chirality

- Before we can discuss stereoisomers, we need to understand chirality.
- Chirality is the property of "handness".

Consider your hands. They are very similar structures, the fingers of each hand extend from the top edge of each palm, while the tumbs extend from the side.

Yet your hands are not identical... they can not be superimposed on top of each other.

Look closely... your hands are mirror images of each other.

- Organic molecules can be chiral if they contain one or more chiral centers.

A chiral center is defined as an sp3 hybridized carbon that is bonded to four different groups.

- Consider the compound 2-bromobutane:

  Model: 
  Mark chiral center: 

The carbon which is bound to the bromine (the red atom) is a chiral center.

It is sp3 hybridized and it is bound to four different groups: a hydrogen (white), a bromine (red), a methyl (-CH3) group and an ethyl (-CH2CH3) group.

The other carbons in this structure are not chiral centers. They are all sp3 hybridized, but each is bonded to at least two hydrogens.

- 2-Fluoro-3-bromobutane has two chiral centers:

  Model: 
  Mark chiral centers: 

The second carbon (C-2) in this molecule (attached to the yellow iodine atom) is sp3 hybridized and bears four different groups: a hydrogen, a fluorine, a methyl group and a -CHBrCH3 group.

Likewise, the third carbon (C-3, attached to the red bromine) is also sp3 hybridized and bears four different groups: a hydrogen, a bromine, a methyl group and a -CHFCH3 group.

The remaining carbons (C-1 and C-4) are both sp3 hybridized but each bears three hydrogens, thus neither is a chiral center.

- If a molecule possess at least one chiral center the possibility of stereoisomers exists.

Copyright 1996 -1999, 2007 by Frank R. Gorga - All rights reserved.

Last Update: 12-Mar-2007