Isomerism

By Dr.Neelam

1. Presented by
Dr. Neelam
Department of chemistry

2. Compoundhavingsamemolecularformulabutdifferentphysical&
chemicalproperties
difference properties because of
different structure
differencepropertiesbecauseof
differentorientation

3. STRUCTURAL ISOMERISM:
Compoundhavingsamemol.formuladifferenceinphysicalpropertiesbecauseof
differentstructure.
(A)Ionisationisomerism:
Thistypeofisomerismoccurswhenthecounterioninacoordinationcompound
isitselfapotentialligandandcandisplacealigandwhichcanthenbecomethe
counterion.
Forexample:
(B)Solvate/hydrateisomerism:
Itoccurswhenwaterformsapartofthecoordinationentityorisoutsideit.Thisis
similartoionisationisomerism.
Forexamples:

4. (C)Linkageisomerism:
Insomeligands,likeambidentateligands,therearetwopossiblecoordination
sites.Insuchcases,linkageisomerismexist.
NO
2groupcanbebondedtometalionsthrough(-NO
2)or(-ONO),
SCN:(-SCN)or(-NCS).
(D)Coordinationisomerism:
Coordinationcompoundsmadeupofcationicandanioniccoordinationentities
showthistypeofisomerismduetotheinterchangeofligandsbetweenthecation
andanionentities.
Forexamples:

5. (E)Ligandisomerism:
Sincemanyligandsareorganiccompoundswhichhavepossibilitiesfor
isomerism,theresultingcomplexescanshowisomerismfromthissource.
Forexample:
ligands1,2-diaminopropane(propylenediamineorpn)and
1,3-diaminopropane(trimethylenediamineortn)
(F)Polymerisationisomerism:
Consideredtobeaspecialcaseofcoordinationisomerism,inthisthevarious
isomersdifferinformulaweightfromoneanother
Forexample:
Theseallhavetheempiricalformula[Pt(NH
3)
2Cl
2] 1:2:2
[Pt(NH
3)
2Cl
2] Pt:NH
3:Cl 1: 2 :2
[Pt(NH
3)
4] [PtCl
4] Pt:NH
3:Cl 2: 4 :4

6. Stereoisomers: Compound having same mol. formula difference in physical
properties because of different orientation.
Geometrical Isomerism
Cisisomer
When ligandsare present on
same side
When ligandsare present at 90
to each other
trans isomer
When ligandsare present on
opposite side
When ligandsare present at 180
to each other

7. Coordination Number Four :
Tetrahedral Complex :
The tetrahedral compounds can not show geometrical isomerism as we all know
that all four positions are equivalent in tetrahedral geometry.
[MA
4], [MA
3B] not show G. I.
Square Planar Complex :
In a square planar complex of formula [MA
2B
2] [A and B are unidentate], the two
ligands.A. may be arranged adjacent to each other in a cisisomer, or opposite to
each other in a trans isomer as depicted.
[MA
2B
2], [M(AB)
2], [MA
2BC], [MABCD] show G. I.

8. Coordination Number 6 :
Geometrical isomerism is also possible in octahedral complexes.
[MA
6], [MA
5B], [M(AA)
3] not show G. I.
[MA
2B
2C
2], [MA
2B
2CD], [MA
2BCE], [MABCDEF], [M(AB)
3], [MA
4B
2], [MA
3B
3]
show G. I.
Optical Isomerism :
Planeofsymmetry
Centerofsymmetry
Axisofsymmetry
Shouldnotbepresent

9. •Tetrahedralcomplexeswithformula[MABCD]showopticalisomersand
octahedralcomplexes(cisform)exhibitopticalisomerism.
•Opticalisomerismiscommoninoctahedralcomplexesinvolvingdidentate
ligands.Cis-isomerof[PtCl
2(en)
2]
2+
showopticalisomerismasshownbelow
becauseoftheabsenceofplaneofsymmetryaswellascentreofsymmetry.

10. 10