What is Plane of Symmetry in Optical Isomerism?
In optical isomerism, a plane of symmetry is an imaginary plane that can divide a molecule into two mirror-image halves.
The plane of symmetry is a crucial concept used to identify whether a molecule is optically active or inactive. According to the provided information, the plane of symmetry method "uses symmetry... to identify optical isomers."
Specifically, it involves the idea of slicing through a coordinate compound (or any molecule) to see if the resulting two parts are exact mirror images of each other. If such a plane exists within the molecule, the molecule is considered to have a plane of symmetry.
How it Relates to Optical Isomerism
Optical isomerism deals with molecules that are non-superimposable mirror images of each other (like your left and right hands). These molecules are called optical isomers or enantiomers, and they are typically optically active, meaning they can rotate plane-polarized light.
A molecule is optically active if and only if it is chiral. Chirality means the molecule is not superimposable on its mirror image. The absence of a plane of symmetry is a key indicator of chirality.
- Presence of a Plane of Symmetry: A molecule possessing a plane of symmetry is achiral and therefore optically inactive. It is superimposable on its mirror image.
- Absence of a Plane of Symmetry: A molecule lacking any plane of symmetry is chiral and therefore optically active. It is not superimposable on its mirror image, existing as one of a pair of enantiomers (optical isomers).
The reference highlights that this method helps "identify optical isomers" by checking for this symmetry element. If a molecule has a plane of symmetry, it cannot exist as a pair of optical isomers in the same way a chiral molecule can.
Practical Identification
To find a plane of symmetry in a molecule:
- Visualize the molecule in 3D space.
- Imagine different planes passing through the molecule (e.g., cutting through atoms, between bonds).
- For each plane, check if the part on one side is the exact mirror image of the part on the other side.
If you find even one such plane, the molecule has a plane of symmetry and is achiral. If, after checking all possibilities, no such plane is found, the molecule is chiral.
In essence, the plane of symmetry is a geometric property that directly correlates with a molecule's potential for optical activity and its ability to form distinct optical isomers.
