Revision of Isomerism

8/4/2019 Revision of Isomerism

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Revision of isomerismRevision of isomerismRevision of isomerismRevision of isomerism1.Structural isomerism1.Structural isomerism

2. Geometrical isomerism2. Geometrical isomerism3.Optical isomerism3.Optical isomerism

4. Conformational isomerism4. Conformational isomerism

ByBy

AjnishAjnish Kumar Gupta (AKG)Kumar Gupta (AKG)

Lecturer of Organic ChemistryLecturer of Organic Chemistry

[email protected]@OrganicChemistry.co.in

www.OrganicChemistry.co.in


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IsomersIsomersTwo or more molecules with same molecular formula but have differentTwo or more molecules with same molecular formula but have different

physical & chemical propertiesphysical & chemical properties

IsomersIsomersTwo or more molecules with same molecular formula but have differentTwo or more molecules with same molecular formula but have different

physical & chemical propertiesphysical & chemical properties


Isomers

Isomers

Structural

i.e Compounds have different IUPAC name

Structural

i.e Compounds have different IUPAC name

Chain

Chain Positional

Positional Functional

Functional Metamer

Metamer Tautomer

Tautomer

Stereo

i.e. Compounds having same IUPAC name

Stereo

i.e. Compounds having same IUPAC name

Configuration

Configuration Conformation

Conformation


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Structural isomerismStructural isomerismChain isomerism :Chain isomerism :

Isomers which differ in main chain or side chain of carbon keeping no

Isomers which differ in main chain or side chain of carbon keeping nochange in nature of chemical reaction, functional groups, multiple bondschange in nature of chemical reaction, functional groups, multiple bonds

oror substituentssubstituents..

Position isomerism :Position isomerism :Isomers which differ in position of functional groups, multiple bonds orIsomers which differ in position of functional groups, multiple bonds orsubstituentssubstituents keeping no change in main skeleton or side skeleton ofkeeping no change in main skeleton or side skeleton of

carbon, functional groups or multiple bonds.carbon, functional groups or multiple bonds.Functional isomerism :Functional isomerism :

Isomers which differ in nature of chemical reactions i.e. mainlyIsomers which differ in nature of chemical reactions i.e. mainlyfunctional groups.functional groups.

MetamerismMetamerism ::Isomers which have any type of difference in carbon along theIsomers which have any type of difference in carbon along the

polyvalent atom containing functional groups which have carbon in bothpolyvalent atom containing functional groups which have carbon in bothsides.sides.

TautomerismTautomerism ::Isomers which differ in position of protons when two structures are inIsomers which differ in position of protons when two structures are in

dynamic equilibrium with each othersdynamic equilibrium with each others

Structural isomerismStructural isomerismChain isomerism :Chain isomerism :

Isomers which differ in main chain or side chain of carbon keeping no

Isomers which differ in main chain or side chain of carbon keeping nochange in nature of chemical reaction, functional groups, multiple bondschange in nature of chemical reaction, functional groups, multiple bonds

oror substituentssubstituents..

Position isomerism :Position isomerism :Isomers which differ in position of functional groups, multiple bonds orIsomers which differ in position of functional groups, multiple bonds orsubstituentssubstituents keeping no change in main skeleton or side skeleton ofkeeping no change in main skeleton or side skeleton of

carbon, functional groups or multiple bonds.carbon, functional groups or multiple bonds.Functional isomerism :Functional isomerism :

Isomers which differ in nature of chemical reactions i.e. mainlyIsomers which differ in nature of chemical reactions i.e. mainlyfunctional groups.functional groups.

MetamerismMetamerism ::Isomers which have any type of difference in carbon along theIsomers which have any type of difference in carbon along the

polyvalent atom containing functional groups which have carbon in bothpolyvalent atom containing functional groups which have carbon in bothsides.sides.

TautomerismTautomerism ::Isomers which differ in position of protons when two structures are inIsomers which differ in position of protons when two structures are in

dynamic equilibrium with each othersdynamic equilibrium with each others



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Geometrical isomerismGeometrical isomerismIsomers which are formed by restriction in rotation in a molecule.Isomers which are formed by restriction in rotation in a molecule.

Conditions:Conditions:1. Molecules must have restriction in rotation1. Molecules must have restriction in rotation2. Restricted atoms must have different2. Restricted atoms must have different substituentssubstituents attach to themattach to them

General cases of Geometrical isomerism :General cases of Geometrical isomerism :1. Along C=C bond1. Along C=C bond2. Along C=N bond2. Along C=N bond

3. Along N=N bond3. Along N=N bond4. Along4. Along cycloalkanescycloalkanes

5. Along5. Along cycloalkenescycloalkenes with carbon 8 or greater than 8with carbon 8 or greater than 8

Some molecules have restriction in rotation but due toSome molecules have restriction in rotation but due toabsence of differentabsence of different substituentssubstituents they dont show GIthey dont show GI

1. Along C=O bond1. Along C=O bond2. Along O=O bond2. Along O=O bond3. Along N=O bond3. Along N=O bond4. Along S=O bond4. Along S=O bond5. Along C5. Along CC bondC bond6. Along C6. Along CN bondN bond

Geometrical isomerismGeometrical isomerismIsomers which are formed by restriction in rotation in a molecule.Isomers which are formed by restriction in rotation in a molecule.

Conditions:Conditions:1. Molecules must have restriction in rotation1. Molecules must have restriction in rotation2. Restricted atoms must have different2. Restricted atoms must have different substituentssubstituents attach to themattach to them

General cases of Geometrical isomerism :General cases of Geometrical isomerism :1. Along C=C bond1. Along C=C bond2. Along C=N bond2. Along C=N bond

3. Along N=N bond3. Along N=N bond4. Along4. Along cycloalkanescycloalkanes

5. Along5. Along cycloalkenescycloalkenes with carbon 8 or greater than 8with carbon 8 or greater than 8

Some molecules have restriction in rotation but due toSome molecules have restriction in rotation but due toabsence of differentabsence of different substituentssubstituents they dont show GIthey dont show GI

1. Along C=O bond1. Along C=O bond2. Along O=O bond2. Along O=O bond3. Along N=O bond3. Along N=O bond4. Along S=O bond4. Along S=O bond5. Along C5. Along CC bondC bond6. Along C6. Along CN bondN bond



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Nomenclature used in GINomenclature used in GICisCis--Trans:Trans:

Mainly used for C=C bonds &Mainly used for C=C bonds & CycloalkanesCycloalkanesCisCis : when 2 similar groups are on the same side of restricted atoms: when 2 similar groups are on the same side of restricted atoms

Trans : when 2 similar groups are on the same side of restricted atomsTrans : when 2 similar groups are on the same side of restricted atoms

SynSyn--Anti:Anti:Mainly used for C=N & N=N bondsMainly used for C=N & N=N bonds

SynSyn : When H & groups are on the same side of restricted atoms when: When H & groups are on the same side of restricted atoms whenderived fromderived from aldehydesaldehydes..When both lone pairs of electrons are on the same side of restrictedWhen both lone pairs of electrons are on the same side of restricted

atoms in N=N bonded compounds.atoms in N=N bonded compounds.Anti : When H & groups are on the opposite side of restricted atomsAnti : When H & groups are on the opposite side of restricted atoms

when derived fromwhen derived from aldehydesaldehydes..When both lone pairs of electrons are on the opposite side ofWhen both lone pairs of electrons are on the opposite side of

restricted atoms in N=N bonded compounds.restricted atoms in N=N bonded compounds.In case of molecules with C=N we have to specify the group on whichIn case of molecules with C=N we have to specify the group on which

we are saying aboutwe are saying about synsyn or anti.or anti.

EE--Z :Z :Next pageNext page

Nomenclature used in GINomenclature used in GICisCis--Trans:Trans:

Mainly used for C=C bonds &Mainly used for C=C bonds & CycloalkanesCycloalkanesCisCis : when 2 similar groups are on the same side of restricted atoms: when 2 similar groups are on the same side of restricted atoms

Trans : when 2 similar groups are on the same side of restricted atomsTrans : when 2 similar groups are on the same side of restricted atoms

SynSyn--Anti:Anti:Mainly used for C=N & N=N bondsMainly used for C=N & N=N bonds

SynSyn : When H & groups are on the same side of restricted atoms when: When H & groups are on the same side of restricted atoms whenderived fromderived from aldehydesaldehydes..When both lone pairs of electrons are on the same side of restrictedWhen both lone pairs of electrons are on the same side of restricted

atoms in N=N bonded compounds.atoms in N=N bonded compounds.Anti : When H & groups are on the opposite side of restricted atomsAnti : When H & groups are on the opposite side of restricted atoms

when derived fromwhen derived from aldehydesaldehydes..When both lone pairs of electrons are on the opposite side ofWhen both lone pairs of electrons are on the opposite side of

restricted atoms in N=N bonded compounds.restricted atoms in N=N bonded compounds.In case of molecules with C=N we have to specify the group on whichIn case of molecules with C=N we have to specify the group on which

we are saying aboutwe are saying about synsyn or anti.or anti.

EE--Z :Z :Next pageNext page



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EE--Z :Z :IUPAC recommended nomenclature used for all geometrical isomersIUPAC recommended nomenclature used for all geometrical isomersGiven by CahnGiven by Cahn--IngoldIngold--Prelog therefore priority rule for decidingPrelog therefore priority rule for deciding

configuration as E or Z is called as CIP Rule.configuration as E or Z is called as C

IP Rule.If two high priority groups are on the same side of restricted atomsIf two high priority groups are on the same side of restricted atoms

than such configuration is called as Z.than such configuration is called as Z.If two high priority groups are on the opposite side of restricted atomsIf two high priority groups are on the opposite side of restricted atoms

than such configuration is called as E.than such configuration is called as E.

CIP Rule :CIP Rule :

1. Group with the first atom having high atomic number directly attach1. Group with the first atom having high atomic number directly attachto restricted atom in case of GI is given higher priority.to restricted atom in case of GI is given higher priority.2. If the first atom is identical then second atom is observed for2. If the first atom is identical then second atom is observed fordeciding the priority. If second is also same then go on up to thatdeciding the priority. If second is also same then go on up to that

place from where we get the difference.place from where we get the difference.3. If the group has3. If the group has unsaturationunsaturation, then a hypothetical equivalent sigma, then a hypothetical equivalent sigma

bond is drawn for it and then compare with other group for seniority.bond is drawn for it and then compare with other group for seniority.4. Only in case of isotopes where atomic number is same but have4. Only in case of isotopes where atomic number is same but havedifferent atomic mass, atomic mass is given higher priority.different atomic mass, atomic mass is given higher priority.

Never correlateNever correlate CisCis--Trans with ETrans with E--Z because both have differentZ because both have differentconcepts for naming configurations.concepts for naming configurations.

CIP Rule is also used to decide RCIP Rule is also used to decide R--SS nomenclatuenomenclatue in optical isomerism.in optical isomerism.

EE--Z :Z :IUPAC recommended nomenclature used for all geometrical isomersIUPAC recommended nomenclature used for all geometrical isomersGiven by CahnGiven by Cahn--IngoldIngold--Prelog therefore priority rule for decidingPrelog therefore priority rule for deciding

configuration as E or Z is called as CIP Rule.configuration as E or Z is called as C

IP Rule.If two high priority groups are on the same side of restricted atomsIf two high priority groups are on the same side of restricted atoms

than such configuration is called as Z.than such configuration is called as Z.If two high priority groups are on the opposite side of restricted atomsIf two high priority groups are on the opposite side of restricted atoms

than such configuration is called as E.than such configuration is called as E.

CIP Rule :CIP Rule :

1. Group with the first atom having high atomic number directly attach1. Group with the first atom having high atomic number directly attachto restricted atom in case of GI is given higher priority.to restricted atom in case of GI is given higher priority.2. If the first atom is identical then second atom is observed for2. If the first atom is identical then second atom is observed fordeciding the priority. If second is also same then go on up to thatdeciding the priority. If second is also same then go on up to that

place from where we get the difference.place from where we get the difference.3. If the group has3. If the group has unsaturationunsaturation, then a hypothetical equivalent sigma, then a hypothetical equivalent sigma

bond is drawn for it and then compare with other group for seniority.bond is drawn for it and then compare with other group for seniority.4. Only in case of isotopes where atomic number is same but have4. Only in case of isotopes where atomic number is same but havedifferent atomic mass, atomic mass is given higher priority.different atomic mass, atomic mass is given higher priority.

Never correlateNever correlate CisCis--Trans with ETrans with E--Z because both have differentZ because both have differentconcepts for naming configurations.concepts for naming configurations.

CIP Rule is also used to decide RCIP Rule is also used to decide R--SS nomenclatuenomenclatue in optical isomerism.in optical isomerism.



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Optical isomerism:Optical isomerism:Experimental backgroundExperimental background: Those compounds which can rotate the plane: Those compounds which can rotate the plane

polarized light to certain angle is called optically active compounds andpolarized light to certain angle is called optically active compounds and

the isomers are called as optical isomers.the isomers are called as optical isomers.TheeoraticalTheeoratical background :background : ChiralityChirality is one & sufficient condition for ais one & sufficient condition for amolecule to be optically activemolecule to be optically active..

ChiralityChirality means dissymmetry ormeans dissymmetry or nonsuperimposabilitynonsuperimposability of an object on itsof an object on itsmirror image i.e. absence of plane of symmetry (POS) & Centre ofmirror image i.e. absence of plane of symmetry (POS) & Centre of

symmetry (COS) .symmetry (COS) .

Dont confuse withDont confuse with chiralchiral molecule andmolecule and chiralchiral carbon, both arecarbon, both aredifferentdifferentChiralChiral carbon is that carbon whose all the fourcarbon is that carbon whose all the four valenciesvalencies are differentare different

butbut chiralchiral molecule is that one which do not have POS & COS.molecule is that one which do not have POS & COS.Symmetric molecules are some times called asSymmetric molecules are some times called as achiralachiral molecules so if amolecules so if a

carbon havecarbon have atleastatleast 2 similar groups then it is2 similar groups then it is achiralachiral carbon.carbon.

Plane of Symmetry (POS):Plane of Symmetry (POS): An imaginary plane that bisects a moleculeAn imaginary plane that bisects a moleculein such a way that the two halves of the molecule are mirror images ofin such a way that the two halves of the molecule are mirror images ofeach othereach other

Centre of Symmetry (COS):Centre of Symmetry (COS): It is the point in the centre of moleculeIt is the point in the centre of moleculefrom which if we move in equal and opposite direction, we get the samefrom which if we move in equal and opposite direction, we get the same

atoms or groups on other side.atoms or groups on other side.

Optical isomerism:Optical isomerism:Experimental backgroundExperimental background: Those compounds which can rotate the plane: Those compounds which can rotate the plane

polarized light to certain angle is called optically active compounds andpolarized light to certain angle is called optically active compounds and

the isomers are called as optical isomers.the isomers are called as optical isomers.TheeoraticalTheeoratical background :background : ChiralityChirality is one & sufficient condition for ais one & sufficient condition for amolecule to be optically activemolecule to be optically active..

ChiralityChirality means dissymmetry ormeans dissymmetry or nonsuperimposabilitynonsuperimposability of an object on itsof an object on itsmirror image i.e. absence of plane of symmetry (POS) & Centre ofmirror image i.e. absence of plane of symmetry (POS) & Centre of

symmetry (COS) .symmetry (COS) .

Dont confuse withDont confuse with chiralchiral molecule andmolecule and chiralchiral carbon, both arecarbon, both aredifferentdifferentChiralChiral carbon is that carbon whose all the fourcarbon is that carbon whose all the four valenciesvalencies are differentare different

butbut chiralchiral molecule is that one which do not have POS & COS.molecule is that one which do not have POS & COS.Symmetric molecules are some times called asSymmetric molecules are some times called as achiralachiral molecules so if amolecules so if a

carbon havecarbon have atleastatleast 2 similar groups then it is2 similar groups then it is achiralachiral carbon.carbon.

Plane of Symmetry (POS):Plane of Symmetry (POS): An imaginary plane that bisects a moleculeAn imaginary plane that bisects a moleculein such a way that the two halves of the molecule are mirror images ofin such a way that the two halves of the molecule are mirror images ofeach othereach other

Centre of Symmetry (COS):Centre of Symmetry (COS): It is the point in the centre of moleculeIt is the point in the centre of moleculefrom which if we move in equal and opposite direction, we get the samefrom which if we move in equal and opposite direction, we get the same

atoms or groups on other side.atoms or groups on other side.



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Basic concepts & picturesBasic concepts & pictures

ss

Basic concepts & picturesBasic concepts & pictures

ss


Chiral molecule- has

the property ofhandednessi.e Notsuperposable on itsmirror imageThey can exist as a

pair of enantiomerswhich are individually

a chiral molecule.Achiral molecule-has property ofSuperposable on itsmirror image.

Mirror images = handedness

Left hand cannot be superimposedon the right hand

Mirror image =converts right handinto left


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Some terms used in optical isomerismSome terms used in optical isomerismEnantiomersEnantiomers :: Two stereo isomers which are nonTwo stereo isomers which are non superimposablesuperimposable but arebut are

mirror images of one another.mirror images of one another.

They have same physical properties so have 1 fraction onThey have same physical properties so have 1 fraction on distilationdistilation..DiastereomersDiastereomers :: Two stereo isomers which are nonTwo stereo isomers which are non superimposablesuperimposable and nonand nonmirror images of one another.mirror images of one another.

They have different physical properties so have 2 fractions onThey have different physical properties so have 2 fractions on distilationdistilation..RacemicRacemic mixture :mixture : Mixture of pair ofMixture of pair of enantiomersenantiomers in equal amounts.in equal amounts.

Compound is optically inactive due to externalCompound is optically inactive due to external compansationcompansation..

MesoMeso compound :compound :Indivisual

Indivisual compound which have plane of symmetry alongcompound which have plane of symmetry alongwithwith chiralchiral centre.centre.

Compound is optically inactive due to internalCompound is optically inactive due to internal compansationcompansation..Specific rotation :Specific rotation : Observed rotation/ConcentrationObserved rotation/Concentration lenghtlenght

Optical purity (OP):Optical purity (OP): Observed optical rotation/Optical rotation of pureObserved optical rotation/Optical rotation of pureenatiomerenatiomer100100

EnantiomericEnantiomeric excess (EE):excess (EE): Excess of oneExcess of one enantiomerenantiomer over other/Entireover other/Entiremixturemixture 100100MathematicallyMathematicallyoptical purity (OP) =optical purity (OP) =enantiomericenantiomeric excess (EE)excess (EE)

Resolution :Resolution : It is a chemical method to separate pair ofIt is a chemical method to separate pair of enantiomersenantiomers..In this methodIn this method enantiomersenantiomers ore first converted intoore first converted into diastereomersdiastereomers byby

reacting with a compound which havereacting with a compound which have chiralchiral carbon and then distill them.carbon and then distill them.

Some terms used in optical isomerismSome terms used in optical isomerismEnantiomersEnantiomers :: Two stereo isomers which are nonTwo stereo isomers which are non superimposablesuperimposable but arebut are

mirror images of one another.mirror images of one another.

They have same physical properties so have 1 fraction onThey have same physical properties so have 1 fraction on distilationdistilation..DiastereomersDiastereomers :: Two stereo isomers which are nonTwo stereo isomers which are non superimposablesuperimposable and nonand nonmirror images of one another.mirror images of one another.

They have different physical properties so have 2 fractions onThey have different physical properties so have 2 fractions on distilationdistilation..RacemicRacemic mixture :mixture : Mixture of pair ofMixture of pair of enantiomersenantiomers in equal amounts.in equal amounts.

Compound is optically inactive due to externalCompound is optically inactive due to external compansationcompansation..

MesoMeso compound :compound :Indivisual

Indivisual compound which have plane of symmetry alongcompound which have plane of symmetry alongwithwith chiralchiral centre.centre.

Compound is optically inactive due to internalCompound is optically inactive due to internal compansationcompansation..Specific rotation :Specific rotation : Observed rotation/ConcentrationObserved rotation/Concentration lenghtlenght

Optical purity (OP):Optical purity (OP): Observed optical rotation/Optical rotation of pureObserved optical rotation/Optical rotation of pureenatiomerenatiomer100100

EnantiomericEnantiomeric excess (EE):excess (EE): Excess of oneExcess of one enantiomerenantiomer over other/Entireover other/Entiremixturemixture 100100MathematicallyMathematicallyoptical purity (OP) =optical purity (OP) =enantiomericenantiomeric excess (EE)excess (EE)

Resolution :Resolution : It is a chemical method to separate pair ofIt is a chemical method to separate pair of enantiomersenantiomers..In this methodIn this method enantiomersenantiomers ore first converted intoore first converted into diastereomersdiastereomers byby

reacting with a compound which havereacting with a compound which have chiralchiral carbon and then distill them.carbon and then distill them.



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SomeSome chiralchiral molecules withoutmolecules without chiralchiral carboncarbon1.1. AllenesAllenes with even no of double bonds & endwith even no of double bonds & end caboncabon have differenthave different

substituentssubstituents..

2.2. SpiranesSpiranes with even no of rings & endwith even no of rings & end caboncabon have differenthave different substituentssubstituents3.3. CycloalkylidinesCycloalkylidines with some of double bonds & rings are even in no andwith some of double bonds & rings are even in no andendend caboncabon have differenthave different substituentssubstituents..

4. Ortho4. Ortho--orthoortho tetra substituted biphenyl with two different substituenttetra substituted biphenyl with two different substituentatat orthoortho position of one phenyl group.position of one phenyl group.

5. Quaternary ammonium salt with all the four5. Quaternary ammonium salt with all the four valanciesvalancies are different.are different.6. Tetravalent phosphorus compounds in which all its four6. Tetravalent phosphorus compounds in which all its four valanciesvalancies areare

different.different.7. Tetravalent7. Tetravalent sulphursulphur compounds in which all its fourcompounds in which all its four valanciesvalancies areare

different.different.8. Tetravalent silicon compounds in which all its four8. Tetravalent silicon compounds in which all its four valanciesvalancies areare

different.different.9. Tetravalent germanium compounds in which all its four9. Tetravalent germanium compounds in which all its four valanciesvalancies areare

different.different.10. Any tetravalent compounds in which all its four10. Any tetravalent compounds in which all its four valanciesvalancies are different.are different.

Basic for a compound to show optical activity isBasic for a compound to show optical activity isnonsuperimposabilitynonsuperimposability i.e. absence of Plane of symmetry & Centrei.e. absence of Plane of symmetry & Centre

of symmetry.of symmetry.

SomeSome chiralchiral molecules withoutmolecules without chiralchiral carboncarbon1.1. AllenesAllenes with even no of double bonds & endwith even no of double bonds & end caboncabon have differenthave different

substituentssubstituents..

2.2. SpiranesSpiranes with even no of rings & endwith even no of rings & end caboncabon have differenthave different substituentssubstituents3.3. CycloalkylidinesCycloalkylidines with some of double bonds & rings are even in no andwith some of double bonds & rings are even in no andendend caboncabon have differenthave different substituentssubstituents..

4. Ortho4. Ortho--orthoortho tetra substituted biphenyl with two different substituenttetra substituted biphenyl with two different substituentatat orthoortho position of one phenyl group.position of one phenyl group.

5. Quaternary ammonium salt with all the four5. Quaternary ammonium salt with all the four valanciesvalancies are different.are different.6. Tetravalent phosphorus compounds in which all its four6. Tetravalent phosphorus compounds in which all its four valanciesvalancies areare

different.different.7. Tetravalent7. Tetravalent sulphursulphur compounds in which all its fourcompounds in which all its four valanciesvalancies areare

different.different.8. Tetravalent silicon compounds in which all its four8. Tetravalent silicon compounds in which all its four valanciesvalancies areare

different.different.9. Tetravalent germanium compounds in which all its four9. Tetravalent germanium compounds in which all its four valanciesvalancies areare

different.different.10. Any tetravalent compounds in which all its four10. Any tetravalent compounds in which all its four valanciesvalancies are different.are different.

Basic for a compound to show optical activity isBasic for a compound to show optical activity isnonsuperimposabilitynonsuperimposability i.e. absence of Plane of symmetry & Centrei.e. absence of Plane of symmetry & Centre

of symmetry.of symmetry.



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Calculation for number ofCalculation for number of sterioisomerssterioisomersCase 1 :Case 1 : ForFor unsymmerticalunsymmertical molecules with nmolecules with n stereocentresstereocentres

No. of stereo isomers =No. of stereo isomers =22nn

Case 2 :Case 2 : ForFor SymmerticalSymmertical molecules with n evenmolecules with n even stereocentresstereocentresNo. of stereo isomers =No. of stereo isomers =22nn 11 ++ 22n/2n/2 11

Case 3 :Case 3 : ForFor SymmerticalSymmertical molecules with n oddmolecules with n odd stereocentresstereocentresCase a :Case a : Central stereo centre is optical in nature :Central stereo centre is optical in nature :

No. of stereo isomers =No. of stereo isomers =22nn 11 ++ 22nn 1/21/2Case b :Case b : Central stereo centre is geometrical in nature :Central stereo centre is geometrical in nature :

No. of stereo isomers =No. of stereo isomers =22nn 11

It is important to remember thatIt is important to remember that stereocentresstereocentres meansmeansany centre along which we can see stereo isomerism i.e.any centre along which we can see stereo isomerism i.e.

Optical or geometrical both.Optical or geometrical both.It may be along C=C,C=N,N=It may be along C=C,C=N,N=N,CycloalkanesN,Cycloalkanes,, CycloalkenesCycloalkenes withwith 8 8 of geometrical or alongof geometrical or along chiralchiral carbon, pseudocarbon, pseudo chiralchiral carbon orcarbon oralong special case ofalong special case of allenesallenes,, spiranesspiranes,, cycloalkylidinecycloalkylidine oror orthoortho--

orthoortho tetra substituted biphenyl.tetra substituted biphenyl.

Calculation for number ofCalculation for number of sterioisomerssterioisomersCase 1 :Case 1 : ForFor unsymmerticalunsymmertical molecules with nmolecules with n stereocentresstereocentres

No. of stereo isomers =No. of stereo isomers =22nn

Case 2 :Case 2 : ForFor SymmerticalSymmertical molecules with n evenmolecules with n even stereocentresstereocentresNo. of stereo isomers =No. of stereo isomers =22nn 11 ++ 22n/2n/2 11

Case 3 :Case 3 : ForFor SymmerticalSymmertical molecules with n oddmolecules with n odd stereocentresstereocentresCase a :Case a : Central stereo centre is optical in nature :Central stereo centre is optical in nature :

No. of stereo isomers =No. of stereo isomers =22nn 11 ++ 22nn 1/21/2Case b :Case b : Central stereo centre is geometrical in nature :Central stereo centre is geometrical in nature :

No. of stereo isomers =No. of stereo isomers =22nn 11

It is important to remember thatIt is important to remember that stereocentresstereocentres meansmeansany centre along which we can see stereo isomerism i.e.any centre along which we can see stereo isomerism i.e.

Optical or geometrical both.Optical or geometrical both.It may be along C=C,C=N,N=It may be along C=C,C=N,N=N,CycloalkanesN,Cycloalkanes,, CycloalkenesCycloalkenes withwith 8 8 of geometrical or alongof geometrical or along chiralchiral carbon, pseudocarbon, pseudo chiralchiral carbon orcarbon oralong special case ofalong special case of allenesallenes,, spiranesspiranes,, cycloalkylidinecycloalkylidine oror orthoortho--

orthoortho tetra substituted biphenyl.tetra substituted biphenyl.



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Some compounds showing eitherSome compounds showing either GI,OI,bothGI,OI,both or noneor noneSome compounds showing eitherSome compounds showing either GI,OI,bothGI,OI,both or noneor none



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