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# Chemical shift equivalence ### Homotopic Atoms & groups are homotopic if a $C_n$ axis of symmetry can interchange them. * Homotopic atoms are always chemical shift equivalent ### Enantiotopic Atoms & groups are enantiotopic if a substitution of one of them with a chiral substituent creates e...

# Chemical shift equivalence ### Homotopic Atoms & groups are homotopic if a $C_n$ axis of symmetry can interchange them. * Homotopic atoms are always chemical shift equivalent ### Enantiotopic Atoms & groups are enantiotopic if a substitution of one of them with a chiral substituent creates enantiomers. * Enantiotopic atoms are chemical shift equivalent unless they are in a chiral environment. ### Diastereotopic Atoms & groups are diastereotopic if a substitution of one of them with a chiral substituent creates diastereomers. * Diastereotopic atoms are NEVER chemical shift equivalent. ## Examples ### Homotopic  * The two $H$ atoms are interchangeable via a $C_2$ axis of symmetry * The two $H$ atoms are homotopic and therefore chemical shift equivalent. ### Enantiotopic  * The two $H$ atoms are enantiotopic. * Replacing one of the $H$ atoms with deuterium would generate a chiral centre, and produce a pair of enantiomers. * In an achiral environment, the two $H$ atoms are chemical shift equivalent. * In a chiral environment, the two $H$ atoms may be chemical shift inequivalent ### Diastereotopic  * The two $H$ atoms are diastereotopic. * Replacing one of the $H$ atoms with deuterium would generate a chiral centre, and produce a pair of diastereomers. * The two $H$ atoms are chemical shift inequivalent ### Summary | Type | Symmetry Relationship | Chemical Shift Equivalence? | | :------------ | :------------------------------------ | :-------------------------- | | Homotopic | $C_n$ axis of symmetry | Yes | | Enantiotopic | Substitution creates enantiomers | Yes (achiral environment) | | Diastereotopic| Substitution creates diastereomers| No |