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Introduction to Organic Chemistry 2 ed William H. Brown

Introduction to Organic Chemistry 2 ed William H. Brown. Amines. Chapter 10. Structure & Classification. Amines are classified as 1°, 2°, or , 3° amines : amines in which 1, 2, or 3 hydrogens of NH 3 are replaced by alkyl or aryl groups

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Introduction to Organic Chemistry 2 ed William H. Brown

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  1. Introduction to Organic Chemistry2 edWilliam H. Brown

  2. Amines Chapter 10

  3. Structure & Classification • Amines are classified as • 1°, 2°, or , 3° amines: amines in which 1, 2, or 3 hydrogens of NH3 are replaced by alkyl or aryl groups • 4° amines: ions in which nitrogen is bonded to four carbons and bears a positive charge

  4. Structure & Classification • Amines are further divided into aliphatic, aromatic, and heterocyclic amines: • aliphatic amines: amines in which nitrogen is bonded only to alkyl groups • aromatic amines: amines in which nitrogen is bonded to one or more aryl groups

  5. Structure & Classification • heterocyclic amines: amines in which nitrogen is one of the atoms of a ring

  6. Nomenclature • Aliphatic amines: replace the suffix -e of the parent alkane by -amine

  7. Nomenclature • The IUPAC system retains the name aniline, the simplest aromatic amine • its simple derivatives are named using the prefixes o, m, p or using numbers to locate substituents

  8. Nomenclature • Among the various functional groups discussed in the text, -NH2 is one of the lowest in order of precedence

  9. Nomenclature • Common names for most aliphatic amines are derived by listing the alkyl groups attached to nitrogen in one word ending with the suffix -amine

  10. Nomenclature • When four groups are bonded to nitrogen, the compound is named as a salt of the corresponding amine

  11. Physical Properties • Amines are polar compounds • both 1° and 2° amines form intermolecular hydrogen bonds • N-H----N hydrogen bonds are weaker than O-H----O hydrogen bonds because the difference in electronegativity between N and H (3.0 - 2.1 =0.9) is not as great as that between O and H (3.5 - 2.1 = 1.4)

  12. Basicity • All amines are weak bases and aqueous solutions of amines are basic

  13. Basicity • It is also common to discuss the basicity of amines by reference to the acid ionization constant of the corresponding conjugate acid • For any acid-conjugate base pair

  14. Basicity • Using values of pKa, we can compare the acidities of amine conjugate acids with other acids • acetic acid is the stronger acid and, therefore, the position of this equilibrium lies to the right • All aliphatic amines have about the same base strength, pKb 3.0 - 4.0, and are slightly stronger bases than ammonia

  15. Basicity-Aliphatic Amines

  16. Basicity-Aromatic Amines • Aromatic amines are considerably weaker bases than aliphatic amines

  17. Basicity-Aromatic Amines • Aromatic amines are weaker bases than aliphatic amines because of the resonance stabilization of the free base, which is lost on protonation

  18. Basicity-Guanidine • Guanidine, pKb 0.4, is the strongest base among neutral organic compounds • its basicity is due to the delocalization of the positive charge over the three nitrogen atoms

  19. Reaction with Acids • All amines, whether soluble or insoluble in water, react quantitatively with strong acids to form water-soluble salts

  20. Amines End Chapter 10

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