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:
- Primary alcohols:
- Moderate migratory aptitude
- Example: CH3CH2OH → CH3CH(OH)CH3
- Secondary alcohols:
- Higher migratory aptitude
- Example: (CH3)2CHOH → CH3C(OH)(CH3)2
- Tertiary alcohols:
- Greatest migratory aptitude
- Example: (CH3)3COH → CH3CO(CH3)3
- Primary alcohols:
- 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
- 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
- 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)
- 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
- 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
- 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
- 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
- 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
- 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)
- 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
- 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
- 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
- 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)
- 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
- 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
- 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
- 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
- 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
- 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)
- 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.
- 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.
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: Primary alcohols: Moderate migratory aptitude Example: CH3CH2OH → CH3CH(OH)CH3 Secondary alcohols: Higher migratory aptitude Example: (CH3)2CHOH → CH3C(OH)(CH3)2 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