Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction to Organic Chemistry 2 ed William H. Brown

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Amines Chapter 10

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Structure & Classification Amines are classified as 1°, 2°, or, 3° amines 1°, 2°, or, 3° amines: amines in which 1, 2, or 3 hydrogens of NH 3 are replaced by alkyl or aryl groups 4° amines 4° amines: ions in which nitrogen is bonded to four carbons and bears a positive charge

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Structure & Classification Amines are further divided into aliphatic, aromatic, and heterocyclic amines: aliphatic amines aliphatic amines: amines in which nitrogen is bonded only to alkyl groups aromatic amines aromatic amines: amines in which nitrogen is bonded to one or more aryl groups

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Structure & Classification heterocyclic amines heterocyclic amines: amines in which nitrogen is one of the atoms of a ring

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature Aliphatic aminese amine Aliphatic amines: replace the suffix -e of the parent alkane by -amine

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature Among the various functional groups discussed in the text, -NH 2 is one of the lowest in order of precedence

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Nomenclature When four groups are bonded to nitrogen, the compound is named as a salt of the corresponding amine

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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 ( =0.9) is not as great as that between O and H ( = 1.4)

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Basicity All amines are weak bases and aqueous solutions of amines are basic

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Basicity Using values of pK a, 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, pK b , and are slightly stronger bases than ammonia

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Basicity-Aliphatic Amines

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Basicity-Aromatic Amines Aromatic amines are considerably weaker bases than aliphatic amines

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Basicity-Guanidine Guanidine, pK b 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

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Reaction with Acids All amines, whether soluble or insoluble in water, react quantitatively with strong acids to form water-soluble salts

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Amines End Chapter 10