# Explain three exaples of Diastereomers ,enantiomers , mesomers ??? With 3D structures

Aug 7, 2018

3D structures will be hard to provide, we can give you two-dimensional pictures...

#### Explanation:

Now diastereomers are geometric isomers that ARE not mirror images. And a simple example is $\text{cis-2-butylene}$ versus $\text{trans-2-butylene}$. Another example could be a molecule with TWO chiral centres, and the $\text{RR}$ and $\text{SR}$ isomers, which are NOT enantiomeric, are diastereomeric. Sometimes, not always, $\text{RS"-="SR}$, but you should consult your text...

Of course enantiomers, are non-superposable mirror-images...

And you also want mesomers...which are resonance isomers...and for this we could go back to inorganic chemistry and consider the $\text{nitrite ion}$...$N {O}_{2}^{-}$.

And I could write the Lewis structure of $\text{nitrite ion}$ as...

O=ddotN-O^(-)harr""^(-)O-ddotN=O

...you can do the same with carbonate or nitrate anions....

Just, apropos of three-dimensional structures, one failing of the modern chemical student is his and her reluctance to use molecular models. These are ALWAYS allowed examination materials, and they seem to be under-utilized....

Given a chiral carbon centre, the interchange of any 2 substituents around that centre gives the enantiomer; interchange again, and it need not be the original 2 substituents, you get the enantiomer of an enantiomer, i.e. the mirror image of a mirror image, i.e. the original isomer. Of course you need to practise how to use them, and you need more practise as to how to represent on the printed page.