Alcohols - Migratory Aptitude of Hydrogen

• Definition: Migratory aptitude refers to the ability of hydrogen to migrate from one carbon to another within a molecule.
• Factors affecting migratory aptitude:
  • Nature of the migrating group
  • Nature of the leaving group
  • Steric hindrance
  • Electronic effects
• Examples with different types of migratory aptitude:
  1. Primary alcohols:
     • Moderate migratory aptitude
     • Example: CH3CH2OH → CH3CH(OH)CH3
  2. Secondary alcohols:
     • Higher migratory aptitude
     • Example: (CH3)2CHOH → CH3C(OH)(CH3)2
  3. Tertiary alcohols:
     • Greatest migratory aptitude
     • Example: (CH3)3COH → CH3CO(CH3)3
• Alcohols containing electron-withdrawing groups:
  • Decrease migratory aptitude
  • Example: CH3C(CN)(OH)(CH3)2 → CH3C(CN)(CH3)(OH)2
• Alcohols containing electron-donating groups:
  • Increase migratory aptitude
  • Example: CH3C(OCH3)(OH)(CH3)2 → CH3C(OCH3)(CH3)(OH)2

11. Steric Hindrance:

• Bulky groups hinder migratory aptitude
• Example:
  • CH3CH2OH → CH3C(CH3)(OH)CH3
  • CH3CH(OH)(CH3)CH3 → CH3C(CH3)(OH)CH3
• Larger alkyl groups make migration difficult

12. Electronic Effects:

• Electron-withdrawing groups decrease migratory aptitude
• Electron-donating groups increase migratory aptitude
• Example:
  • CH3CH(OH)(CH3)(Cl) → CH3C(Cl)(OH)(CH3)
  • CH3CH(OH)(CH3)(NO2) → CH3C(NO2)(OH)(CH3)

13. Migratory Aptitude in E1 Reactions:

• In elimination reactions, migratory aptitude affects the final product
• More migratory aptitude leads to more substitution
• Example:
  • CH3CH2OH → H2O + CH3CH=CH2
  • CH3CH(OH)(CH3) → H2O + CH3C(CH3)=CH2

14. Comparison with Other Leaving Groups:

• Hydrogen as a leaving group has lower migratory aptitude compared to other leaving groups
• Example:
  • CH3CH2OH → CH3CH2Cl
  • CH3CH(OH)(CH3) → CH3C(CH3)Br

15. Migratory Aptitude in E2 Reactions:

• In elimination reactions, migratory aptitude affects the reaction mechanism
• More migratory aptitude leads to more product formation
• Example:
  • CH3CH2OH + NaOH → H2O + CH3CH2ONa
  • CH3CH(OH)(CH3) + NaOH → H2O + CH3C(CH3)ONa

16. Reactivity of Different Alcohols:

• Reactivity depends on the migratory aptitude of the alcohol
• Primary alcohols have moderate reactivity
• Secondary alcohols have higher reactivity
• Tertiary alcohols have the highest reactivity

17. Application in Organic Synthesis:

• Understanding migratory aptitude helps in predicting and controlling reactions
• Useful in designing synthesis routes for complex organic molecules
• Example:
  • Formation of a specific alcohol isomer
  • Synthesis of pharmaceutical compounds

18. Stereospecificity in Reactions:

• Migratory aptitude can have stereochemical implications
• Example:
  • CH3CH(OH)(CH3) → CH3C(CH3)(OH)CH3 (retention of configuration)
  • CH3CH(OH)(CH3) → CH3C(H)(CH3)(OH)CH3 (inversion of configuration)

19. Limitations of Migratory Aptitude:

• Migratory aptitude is a general trend, but exceptions exist
• Other factors can influence reaction outcomes
• Example:
  • Effects of temperature and pressure
  • Effects of solvent and reaction conditions

20. Summary:

• Migratory aptitude refers to hydrogen migration in alcohols
• Primary alcohols have moderate migratory aptitude
• Secondary alcohols have higher migratory aptitude
• Tertiary alcohols have the greatest migratory aptitude
• Factors affecting migratory aptitude include steric hindrance and electronic effects

21. Steric Hindrance Effects:

• Bulky groups hinder migratory aptitude.
• Steric hindrance can prevent the migration of hydrogen.
• Example:
  • CH3CH2OH → CH3C(CH3)(OH)CH3
  • CH3CH(OH)(CH3)CH3 → CH3C(CH3)(OH)CH3

22. Electronic Effects:

• Electron-withdrawing groups decrease migratory aptitude.
• Electron-donating groups increase migratory aptitude.
• Example:
  • CH3CH(OH)(CH3)(Cl) → CH3C(Cl)(OH)(CH3)
  • CH3CH(OH)(CH3)(NO2) → CH3C(NO2)(OH)(CH3)

23. Comparison with Other Leaving Groups:

• Hydrogen as a leaving group has lower migratory aptitude compared to other leaving groups.
• Leaving groups can be halides or other functional groups.
• Example:
  • CH3CH2OH → CH3CH2Cl
  • CH3CH(OH)(CH3) → CH3C(CH3)Br

24. Migratory Aptitude in E1 Reactions:

• E1 reactions involve the removal of a leaving group and formation of a double bond.
• Migratory aptitude affects the final product in E1 reactions.
• Example:
  • CH3CH2OH → H2O + CH3CH=CH2
  • CH3CH(OH)(CH3) → H2O + CH3C(CH3)=CH2

25. Migratory Aptitude in E2 Reactions:

• E2 reactions involve the removal of a leaving group and formation of a double bond.
• Migratory aptitude affects the reaction mechanism in E2 reactions.
• Example:
  • CH3CH2OH + NaOH → H2O + CH3CH2ONa
  • CH3CH(OH)(CH3) + NaOH → H2O + CH3C(CH3)ONa

26. Reactivity of Different Alcohols:

• Reactivity of alcohols depends on the migratory aptitude of the alcohol.
• Primary alcohols have moderate reactivity.
• Secondary alcohols have higher reactivity.
• Tertiary alcohols have the highest reactivity.
• Example:
  • CH3CH2OH
  • (CH3)2CHOH
  • (CH3)3COH

27. Application in Organic Synthesis:

• Understanding migratory aptitude helps in predicting and controlling reactions in organic synthesis.
• It allows the design of synthesis routes for complex organic molecules.
• Example:
  • Synthesis of pharmaceutical compounds

28. Stereospecificity in Reactions:

• Migratory aptitude can have stereochemical implications.
• In certain reactions, the configuration of the molecule can be affected.
• Example:
  • CH3CH(OH)(CH3) → CH3C(CH3)(OH)CH3 (retention of configuration)
  • CH3CH(OH)(CH3) → CH3C(H)(CH3)(OH)CH3 (inversion of configuration)

29. Limitations of Migratory Aptitude:

• Migratory aptitude is a general trend, but there can be exceptions.
• Other factors can influence reaction outcomes.
• Example:
  • Effects of temperature and pressure.
  • Effects of solvent and reaction conditions.

30. Summary:

• Migratory aptitude refers to the ability of hydrogen to migrate within a molecule.
• Primary alcohols have moderate migratory aptitude.
• Secondary alcohols have higher migratory aptitude.
• Tertiary alcohols have the greatest migratory aptitude.
• Factors affecting migratory aptitude include steric hindrance and electronic effects.