Isomers (Part 1 of 2)
You can find the second part of this series here: Isomers (Part 2 of 2).
Isomers may also be called Structural Isomers, or Constitutional Isomers.
Isomers are molecules that have the same molecular formula, but a different arrangement of atoms in space. I.e. same number of atoms – but different structure.
- These have the same molecular formula but have different structures
- Thus, they are different molecules, and have different properties
Note: the bonds without denoted C or H atoms are assumed to have Hydrogens attached in Chemistry
Geometric isomers are molecules that are locked into their spatial positions with respect to one another. This is due to a double bond or ring structure.
- Both of these molecules are But-2-ene
Ais Trans-But-2-ene, or (E)-But-2-ene
Bis Cis-But-2-ene, or (Z)-But-2-ene
Trans (E) = Opposite
Cis (Z) = The same
Optical isomers are molecules that differ three-dimensionally by the placement of substituents around one or more atoms in a molecule.
A‘s bond to Cl is coming towards the read in the third dimension
B‘s bond to Cl is moving away, into the screen/page in the third dimension
Optical isomers are also enantiomers. These molecules differ in only one characteristic – i.e. how they interact with polarised light.
Optical isomers are mirror images that are non-superimposable on each other.
The red line representing a mirror
- From above, rotating B (A’s Mirror image) in any direction will not allow you to superimpose it directly on top
- The Cl atom in B will be facing the other way when rotated
This introduces the idea of Chirality. This is covered in the second part of this series on Isomers.