1. AMINES Dr. Sheppard CHEM 2412 Fall 2014 McMurry (8 th ed.) sections:24.2, 24.3, 24.4, 24.6, 24.7, 24.9, 24.10

2. Amines Derivatives of ammonia Neurotransmitters Medicines Amino acids, nucleic acids

3. Amines I. Nomenclature Review II. Structure III. Spectroscopy IV. Physical Properties V. Basicity VI. Preparation VII. Reactions

4. I. Nomenclature (Review) 1. Parent chain is longest containing C bonded to –N 2. Change suffix “-e” to “-amine” 3. Number from end closest to –N. Show location of –N. 4. Name/number substituents 5. -NH 2 as a substituent is “amino” Order of precedence of functions

5. I. Nomenclature (Review) Common name system for amines Name alkyl group(s) List in alphabetical order Add “amine” Examples: StructureName CH 3 CH 2 NHCH 3 (CH 3 CH 2 ) 2 NH

6. I. Nomenclature (Review) Aromatic amines StructureName

7. I. Nomenclature (Review) Pyridine If substituted, nitrogen is atom 1 of the ring. Number in direction of other substituents.

8. II. Structure Classification as 1°, 2°, 3°, 4°

9. II. Structure Geometry Hybridization of N? Electron arrangement = tetrahedral Shape = pyramidal Bond angle around N? Amines can be chiral Not easily separated form enantiomer (unless 4° ammonium salt) Nitrogen inversion (pyramidal inversion)

10. III. Spectroscopy of Amines: IR Absorption(s) at 3300-3500 cm -1 for N-H

11. 13 C-NMR: Atoms bonded to N are deshielded 1 H-NMR: N-H signal shifts around from  2-5 N-H signal is usually broad and shows no splitting Hydrogens on carbons adjacent to N at  2.2-2.6 III. Spectroscopy of Amines: NMR

12. III. Spectroscopy of Amines: MS Nitrogen rule: if a molecule has an odd number of nitrogen atoms, the mass will be an odd number Odd masses have 1 or 3 nitrogen atoms Even masses have 0 or 2 nitrogen atoms Molecule fragments by carbon bonded to amine  -cleavage

13. III. Spectroscopy of Amines: MS Ex: ethylpropylamine

14. Amines are strongly polar Primary and secondary amines form H-bonds (neat) Tertiary amines only accept H-bonds from donor (e.g. H 2 O) Boiling points Higher than hydrocarbons; lower than alcohols (why?) Tertiary amines lower than primary or secondary Quaternary salts = ionic = very high MP and BP Solubility Low MW soluble in water; decreases as MW increases Salts of amines are more soluble in water than neutral amines IV. Physical Properties of Amines

15. Odor Low MW amines = fishy Higher MW amines: IV. Physical Properties of Amines

16. V. Basicity of Amines Amines have lone pair on N More basic than alcohols (more stable conjugate acid) More basic than amides (amides stabilized by resonance)

17. V. Basicity of Amines Trends in basicity Tertiary, secondary, and primary amines are all approximately equal in basicity Conjugated acids of primary are better solvated, but those of tertiary amines are more stable through induction Primary, secondary and tertiary amines are all stronger bases than ammonia Note pK a values for conjugate acid Lower pK a indicates weaker base

18. V. Basicity of Amines Aromatic amines are weaker bases than aliphatic amines Aniline Stabilized by resonance Less basic/nucleophilic Pyrrole (a heterocycle) Loses its aromaticity when protonated (Chapter 15 later this semester), so less basic

19. V. Basicity of Amines sp-hybridized N’s are less basic than sp 2 -hybridized N’s, which are less basic than sp 3 -hybridized N’s More s-character holds electrons more tightly Electrons are less available/less basic Note pK b values for amine Lower pK b indicates stronger base

20. VI. Preparation of Amines 1. S N 2 reactions with alkyl halides Often yields multiple substitution products Products can continue to act as nucleophiles

21. VI. Preparation of Amines 2. Reduction of nitriles 3. Reduction of amides

22. VI. Preparation of Amines 4. Reduction of aromatic nitro groups

23. VI. Preparation of Amines 5. Reductive amination

24. VII. Reactions of Amines 1. Alkylation (S N 2 with alkyl halide) 2. Formation of imine (as in reductive amination) 3. Nucleophilic acyl substitution Product = amide Will see in carboxylic acid derivative chapter