Symmetric Elements and Chirality

The existence of a single chiral center point to chirality’s of a molecule. a new way to know chirality is to detect the existence of some symmetry elements.

A molecule will not be chiral if it haves.:-

• A plane of symmetry (s)
• A center of symmetry 
• An n fold alternating axis of symmetry (S_n or C_n) where n is an even number.
• These three are known as elements of symmetry.

Plane of symmetry

Plane of symmetry

A plane that separates an object into two equal halves is known as plane of symmetry. Its also known as mirror plane at the same time as it cuts a molecule into two parts, where one is the mirror image of the other. Molecules having such a plane are for all time inactive because of inside compensation. For e.g., meso tartaric acid has a plane of symmetry.

Mesotartaric acid

There are two symmetric carbon atoms.  They are consequently achiral. Therefore meso tartaric acid is optically inactive.

Center of symmetry

Center of symmetry

The center of symmetry is an imaginary point in the molecule. If a line is drained from an atom or a group of the molecule to this imaginary point and then comprehensive to an equal distance ahead of the point, it meets the mirror image of the atom or group. For e.g., trans-1, 4-dimethyl-diketopiperazine has a axis of symmetry and consequently optically inactive.

If a line is strained from methyl group on carbon 1 to the center of symmetry and comprehensive away from this point by an equal distance it meets the methyl group at carbon 4, consequently it is optically inactive.

Alternating axis of symmetry

Alternating axis of symmetry

When a structure is spin throughout an angle of 2p/n about an imaginary axis and then reflects across a plane perpendicular to the axis, an identical composition results.