How to Determine if a Molecule is Optically Active

[nemzy]

how do we know if a molecule is optically active?

does it have to do something about R,S configurations? I have no idea, what it is...and how to know whether a molecule is optically active or not

thanks

 

[vinter]

The only sure test to see whether a molecule is optically active or not is to make a model and see whether its mirror image is super-imposable on it or not. If it is superimposable, it's not optically active.

Another good but not sure test is to search for a chiral atom, i.e, an atom with all groups attached to it being different. If the molecule has only one chiral atom, it is sure to be optically active, but if it has more than one chiral atoms, you will have to perform other tests.

 

[so-crates]

The only sure test to see whether a molecule is optically active or not is to make a model and see whether its mirror image is super-imposable on it or not. If it is superimposable, it's not optically active.

That would be superposable, not superimposable. Any two things can be superimposed, but not everything can be superposed :-)