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Chapter 10, Table of Contents 1. Structure & Classification 2. Nomenclature 3. Physical Properties and Structure of Amines 4. Basicity of Amines: Salts 5. PKa and pKb 6. Reactions with 7. Amines as

Structure & Classification Structure & Classification • Classification • Amines are further divided into aliphatic, – 1°, 2°, or , 3° amines: Amines in which 1, 2, or 3 aromatic, and heterocyclic amines. – Aliphatic amine: An amine in which is of NH3 are replaced by or groups. bonded only to alkyl groups. – Aromatic amine: An amine in which nitrogen is bonded to one or more aryl groups.

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Structure & Classification Structure & Classification – Heterocyclic amine: An amine in which nitrogen is one of the of a ring. • Example: Classify each amino group by type.

Aliphatic Amines: Replace the suffix of the parent Nomenclature by –amine. • The IUPAC system retains the common name .

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Nomenclature Nomenclature • Common names for most aliphatic amines are • Among the various functional groups derived by listing the alkyl groups bonded to discussed in the text, ‐NH group has one of 2 nitrogen in one word ending with the suffix ‐ the lowest priorities. amine.

Nomenclature Physical Properties • When four groups are bonded to the nitrogen • Amines are polar compounds, and both 1° and , we name the compound as a salt of the 2° amines form intermolecular corresponding amine. 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 less than that between O and H (3.5 ‐ 2.1 = 1.4).

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Basicity Basicity • All amines are weak bases, and aqueous • It is also common to discuss the basicity of solutions of amines are basic. amines by reference to the ionization constant Ka of its conjugate .

– For any acid‐conjugate pair.

Basicity Basicity – Aliphatic amines have about the same base strength, pK 3.0 –4.0 and are slightly • Using values of pK , we can predict the position of b a stronger bases than NH . equilibrium in acid‐base reactions. 3

– Acetic acid is the stronger acid and, therefore, the position of this equilibrium lies to the right.

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Basicity Basicity – Aromatic amines are considerably weaker bases Aromatic amines are weaker bases than aliphatic amines than aliphatic amines. because the resonance stabilization of the is lost on .

Basicity Basicity • Electron‐withdrawing groups, such as halogen, • Example: Select the stronger base in each pair nitro, and carbonyl, decrease the basicity of of amines. aromatic amines by decreasing the availability of the electron pair on nitrogen.

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Guanidine Reaction with Acids • (pKb 0.4) is the strongest base among neutral organic compounds. • All amines, whether soluble or insoluble in water, react quantitatively with strong acids to form water‐ soluble salts.

– Its basicity is due to the resonance delocalization of the positive charge over the three nitrogen atoms.

Amines as Nucleophiles Amines as Nucleophiles • Reaction of an amine with an alkyl halide can be used to form a new covalent bond. • Step 2: Take a proton away. Converts the amine salt to a free amine. Step 1: Reaction of a with an electrophile to form a new covalent bond.

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