04 1 / 2013

Optical activity in Inorganic compounds

For a long time the only optically active isomers known were organic compounds. This is understandable because, as discussed previously, chirality arises when one atom has four bonds to four different groups; and carbon is one of few atoms that easily forms four such bonds. And while that is by far the most common form of optical activity, there is another.

If a central atom has three groups that each bind to it twice you get a propeller-looking arrangement in the compound. This leads to optical activity since a propeller has an intrinsic spin to its blades. They can be thought of as pointing clockwise or anticlockwise. If the compound in question has a spin clockwise it will rotate light in a different direction from its isomer with an anticlockwise spin.

In the early 1900’s Alfred Werner discovered the optical activity of a cobalt compound known as hexol (pictured below). If you look you should be able to see the propeller-like chirality of the central cobalt atom. This discovery overthrew the assumption that chirality was inherent only to organic compounds. Alfred Werner won the Nobel Prize for Chemistry in 1913. He was the first inorganic chemist to ever win it; furthermore, no inorganic chemist won the Nobel Prize for the next 60 years.


(Source: Wikipedia)

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