CHE2C Isomers

what are isomers? and why does this happen?

• compounds that have same structure but different physical and/or chemical characters

• this happens because it is possible that the arrangement or bonding is different between the two molecules

structure isomers

• contain the same type and number of atoms but different bonding

  • two types:

    • coordination isomers and linkage isomers

coordination isomers

• type of structure

  • the ligand switch with the counter ion

  • when TM of bimetallic complex switch ligands

linkage isomers

• type of structure

  • composition of complex ion is the same but the point of attachment of one ligand will differ

    • some ligands are able to bind from both sides

stereoisomers

• have the same bonding but different arrangement in space

  • different types

    • geomtric isomers (cis-trans isomers)

    • optical isomers

geometric isomers

• cis-trans isomers and type of stereoisomers

  • atoms can take different positions around a rigid ring or bond

• Cis = 2 identical groups on the same side of the metal

  • sharing an edge

• Trans = 2 identical groups on different sides of the metal

optical isomers

• type of stereoisomers

  • have opposite effect on plane polarized light

  • rotates the plane of polarized light left or right

• those that actively change the direction of light are “optically active”

what makes something optically active?

• optical isomers that actively change the direction of light

• compounds that have a nonsuperimposable mirror image

  • known as chiral compound

nonsuperimposable

• you cannot rotate one to become the other

superimposable

• you can rotate one to become the other

Chiral Rules

1) tetrahedral can only be chiral if it has 4 different ligands

2) octahedral can only be chiral in the following cases

• all 6 ligands are different

• only 2 monodentate ligand are same and cis, while the rest 4 are different

• 3 cis pairs

• 3 bidentate ligands

• 2 bidentate ligands in cis position

Dextrorotatory

• if rotation to the right we call it (d)isomer

levorotatory

• if rotation to left we call it (L)isomer

racemic mixture

• solution containing an equal mixture of d and L forms

  • does not rotate the plane of the polarized light as the opposite effects cancel each other