The document discusses prochirality and topicity in organic chemistry, defining prochiral molecules and various types of homomorphic ligands and their relationships. It explains the criteria for identifying homotopic, heterotopic, enantiotopic, and diastereotopic ligands based on substitution, addition reactions, and symmetry. Additionally, it covers the stereochemical aspects of these ligands and their implications in molecular structure and reactivity.

1. a a
b c
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2. PROSTEREOISOMERISM / PROCHIRALITY
• Prochirilty molecules are those which are converted into chiral
molecule in a single step.
• Prochirality may be the result of substitution reaction of sp³ carbon
with nucleophile.
OR
• Prochirality may be the result of addition reaction of sp²carbon to a
sp³ carbon with nucleophile. a a
b c
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3. Prochirality may be the result of substitution reaction of sp³ hybridized carbon
substituent.
a ab c
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4. Prochirality may be the result of addition reaction of sp² hybridized carbon.
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5. Topicity can be defined as geometrical or stereochemical relationship between homorphic groups /
ligands/ atoms and structure of the molecule.
Difference types of relationships are possible for homomorphic ligands/groups/atoms.
1.Homo topic(homo-same; topo-place)
2.Hetero topic(hetero-different; topo-place)
Ligands can not by itself be called homotopic or heterotopic , in order to use this terminologies a
comparison with other homomorphic ligand or ligands present either in the same molecule or in a
different molecule is necessary.
Two criteria are used to decide whether the ligands/groups are equivalent or not.
a. Substitution-addition reaction
b. Symmetry criteria
Are employed to determine the topic relationship of homomorphic ligands.
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6. NOTE:
Homomorphic groups/ligands/atoms:
The groups/ ligands/atoms which are in isolation look the same or superimposable mirror images of each
other are called homomorphic groups/ligands/atoms.
Incase of atoms they must be of same element example two H’s or two Br atoms.
If we isolate the two H’s, then they are same and super imposable to each other
hence they are called homomorphic hydrogen’s.
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7. Incase of groups ,they must have same constitution and configuration. For example two methyl or
two Ph groups of same chirality R or S. They are called homomorphic groups / ligands / atoms.
a a
b c
A. Homotopic ligands :
Two or more ligands that are identical when viewed in isolation but
individual replacement of two identical ligand by another give rise
to identical molecule ,then they are called homotopic ligands.
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8. a
b c
a
1) Substitution-addition criteria
Two homomorphic ligands are homo tropic if substitution of first one and other by
different test ligand leads to homomers or identitical product.
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9. a a
b c
b.Homo topic faces
Two face of a pi system or a double bond are homotopic if addition to
either faces gives same or identical product.
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10. a a
b c
2)Symmetry criteria
a. Homo topic ligands
Two homomorphic ligands are homotopic if they can interchange position by rotation around Cn axis.
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11. a ab c
b.Homo topic faces
Two faces of pi system are homotopic if they can interchange face
result in structure by rotation around C2 axis.
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12. a a
b c
Heterotopic ligands
Two or more ligands that are identical when viewed in isolation but individual replacement of identical ligands by
another ligad give rise to two structurally different(isomeric) molecules, then they are called heterotopic ligands.
Constitutionally hetero topic ligands
Two or more ligands in a molecule that are identical on individual replacement
by another ligand give rise to two molecules that constitutional isomer of each
other, then the original two ligands are said to be constitutionally heterotopic
ligands.
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13. a ab c Stereo chemically hetero topic
Two or more ligands in a molecule that are identical on individual
replacement by another ligand give rise to two moecules that are
enantiomers/super imposable mirror images of each other,then the original
two ligands are said to be enantiotopic ligands.
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14. a a
b c
a)Enantiotopic ligands
1.Substitution-addition criteria
Two homomorphic ligands are enantiotopic if substitution of first one and other by different ligand leads to
enantiomers.
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15. a a
b c
b)Enantiotopic faces
Two faces of a pi system or a double bond are enantiotopic if addition to
either face gives enantiomeric product.
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16. a a
b c
Molecules having stereo heterotopic ligands exhibit prochirality.
2.Symmetry criteria
a)Enantiotopic ligand
Two homomorphic ligands are enantiotopic if they can interchangeable
through plane of symmetry or centre of inversion or Sn axis.
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17. a a
b c
Example-1: Molecule with plane of symmetry (ϭ) containing homomorphic ligand is
enantiotopic.
Example 2:Molecules with improper axis of symmetry (Sn)
containing homomorphic ligand is enantiomer.
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18. a a
b c
b)Enantiotopic faces
Two faces are enantiotopic if they can interchange through plane of symmetry or center of inversion of Sn
axis.
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19. a a
b c
a)Diastereotopic ligands
Two or more ligands in a molecule that are identical on individual replacement by another ligand give rise to
two molecule that are diastereomers/non superimposable not mirror images of each other, then the original
two ligands are said to be diastereotopic ligands.
Substitution–addition criteria
Two homomorphic ligands are diastereotopic if substitution of first one and the other by different test ligand
not already attached to the molecule leads to diastereomers /non superimposable not mirror images.
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20. a a
b c
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21. a a
b c
b)Diastereotopic faces
Two faces of a carbonyl group adjacent to stereo center upon
addition reaction leads to diastereomers and possess diastereotopic
faces.
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22. a a
b c
Wash your NON-SUPERIMPOSABLE(hands)
Stay as TRANS(social distancing)
Stay as CHAIR(Home)
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