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Chapter 15

Chapter 15. Amines. Structure & Classification. Amines are classified as 1°, 2°, or 3° depending on the number of carbon groups bonded to nitrogen. Structure & Classification. heterocyclic amine: an amine in which the nitrogen atom is part of a ring. Nomenclature. IUPAC names

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Chapter 15

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  1. Chapter 15 Amines

  2. Structure & Classification • Amines are classified as 1°, 2°, or 3° depending on the number of carbon groups bonded to nitrogen

  3. Structure & Classification • heterocyclic amine: an amine in which the nitrogen atom is part of a ring

  4. Nomenclature • IUPAC names • Similar to alcohols • drop the final -e of the parent alkane and replace it by -amine • use a number to locate the amino group on the parent chain

  5. Nomenclature • IUPAC names (cont’d) • IUPAC nomenclature retains the common name aniline for C6H5NH2, the simplest aromatic amine • use numbers to locate substituents or, alternatively, use the prefixes ortho (o), meta (m), and para (p) • common names are still widely used

  6. Nomenclature • IUPAC names (cont’d) • name unsymmetrical secondary and tertiary amines as N-substituted primary amines • take the largest group bonded to nitrogen as the parent amine • smaller group(s) are substituents indicated by using the prefix N

  7. Nomenclature • Common names • for most aliphatic amines, list the groups bonded to nitrogen in alphabetical order in one word ending in the suffix -amine

  8. Nomenclature • Amine salts • when four things are bonded to a nitrogen atom, the nitrogen bears a positive charge • name the compound as a salt • replace the ending -amine (or aniline or pyridine or the like) by -ammonium (or anilinium or pyridinium or the like) and add the name of the anion

  9. Physical Properties • Like ammonia, low-molecular-weight amines have very sharp, penetrating odors • trimethylamine, for example, is the pungent principle in the smell of rotting fish • two other particularly pungent amines are 1,4-butanediamine (putrescine) and 1,5-pentanediamine (cadaverine)

  10. Physical Properties • Amines are polar compounds • both 1° and 2° amines have N-H bonds, and can form hydrogen bonds with one another

  11. Physical Properties • an N-H---N hydrogen bond is weaker than an O-H---O hydrogen bond • compare the boiling points of ethane, methanamine, and methanol

  12. Physical Properties • all classes of amines form hydrogen bonds with water and are more soluble in water than are hydrocarbons of comparable molecular weight • most low-molecular-weight amines are completely soluble in water • higher-molecular-weight amines are only moderately soluble in water or are insoluble

  13. Basicity of Amines • Like ammonia, amines are weak bases, and aqueous solutions of amines are basic • the acid-base reaction between an amine and water involves transfer of a proton from water to the amine

  14. Basicity of Amines • The base dissociation constant, Kb, for the reaction of an amine with water has the following form, illustrated for the reaction of methylamine with water to give methylammonium hydroxide • pKb is defined as the negative logarithm of Kb

  15. Basicity of Amines • aliphatic amines SS bases than NH3 • aromatic amines are weaker bases

  16. Basicity of Amines • We can determine which form of an amine exists in body fluids, pH 7.40 • if an aliphatic amine is dissolved in blood, it is present predominantly as its protonated (conjugated acid) form

  17. Reactions of Amines • The most important chemical property of amines is their basicity • amines, whether soluble or insoluble in water, react quantitatively with strong acids to form water-soluble salts

  18. Reactions of Amines • example: complete each acid-base reaction and name the salt formed

  19. Reactions of Amines • example: complete each acid-base reaction and name the salt formed • solution:

  20. Synthesis of Amines • 1) Alkyl halides react with ammonia to make primary amines • This can lead to multiple amination products • Example on board • 2) Alkyl halides may be reacted with cyanide and then hydrogenated to for the primary amine exclusively. • Example on board

  21. Reactions of Amines • 3) Aldehydes and ketones can condense with primary amines and then be hydrogenated to for secondary amines • Example on the board

  22. Amines End Chapter 16

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