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Spectroscopy of Amines - IR

keely-graham
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Spectroscopy of Amines - IR

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  1. Characteristic N–H stretching absorptions 3300 to 3500 cm-1. NH2 group shows an irregular doublet, NH - weak multiple bands. Ammonium ions show N-H at 2600 cm-1.Amine absorption bands are sharper and less intense than hydroxyl bands. 1o amines show NH2 deformation band at 1650-1590 cm-1. C-N stretching vibrations are found at 1090-1068 cm-1 in 1o amines with a 1oa carbon, 1140-1080 cm-1 with a 2oa carbon, and at 1240-1170 cm-1 with a 3oa carbon. 3o amines show no C-N vibrations. In aromatic amines, this band is at 1330-1260 cm-1. N-H wagging bands are found at 850-750 cm-1 as strong, broad, multiple bands. These are weak in aromatic amines. Spectroscopy of Amines - IR

  2. Since N is a compound with an odd number of nitrogen atoms has an odd-numbered molecular weight and a corresponding parent ion Alkylamines cleave at the C–C bond nearest the nitrogen to yield an alkyl radical and a nitrogen-containing cation Mass Spectrometry

  3. The two modes of a cleavage give fragment ions at m/z = 58 and m/z = 72. Mass Spectrum of N-Ethylpropylamine

  4. N–H hydrogens appear as broad signals, either fully coupled to neighboring C–H hydrogens, or more frequently with no coupling (just like the H-bonded OH signals) Hydrogens on C next to N and absorb at lower field than alkane hydrogens N-CH3 gives a sharp three-H singlet at δ2.2 to 2.6 1H - NMR Spectroscopy

  5. C3H9NO

  6. C4H11NO2

  7. C8H11NO

  8. C9H13N

  9. C15H17N

  10. C6H15N - IR

  11. C6H15N - 1H-NMR

  12. Organic derivatives of ammonia, NH3 Nitrogen atom with a lone pair of electrons, making amines both basic and nucleophilic Occur in plants and animals Structure, Properties and Reactivity of Amines

  13. For simple amines, the suffix -amine is added to the name of the alkyl substituent IUPAC nomenclature of simple amines • The suffix -amine can also be used in place of the final -e in the name of the parent compound

  14. Alkyl-substituted (alkylamines) or aryl-substituted (arylamines) Classified: 1° (RNH2), methyl (CH3NH2), 2° (R2NH), 3° (R3N) IUPAC nomenclature of simple amines

  15. Consider the NH2 as an amino substituent on the parent molecule IUPAC nomenclature of complex amines.Amines with more than one functional group.

  16. Symmetrical secondary and tertiary amines are named by adding the prefix di- or tri- to the alkyl group IUPAC nomenclature of complex amines.Amines withmultiple alkyl groups.

  17. Named as N-substituted primary amines Largest alkyl group is the parent name, and other alkyl groups are considered N-substituents IUPAC nomenclature of complex amines.Amines withmultiple different alkyl groups.

  18. Alkylamines do not have common names unless they are biological molecules, such as putrycine (1,6-hexanediamine) or cadaverine (1,7-heptanediamine) Simple arylamines have common names Common Names

  19. If the nitrogen atom occurs as part of a ring, the compound is designated as being heterocyclic Each ring system has its own parent name Common Names of Heterocyclic Amines

  20. A nitrogen atom with four attached groups is positively charged Compounds are quaternary ammonium salts Quaternary Ammonium Ions

  21. Bonding to N is similar to that in ammonia N is sp3-hybridized C–N–C bond angles are close to 109° tetrahedral value Structure and Bonding in Amines

  22. The lone pair of electrons on nitrogen makes amines basic and nucleophilic They react with acids to form acid–base salts and they react with electrophiles Amines are stronger bases than alcohols, ethers, or water Amines establish an equilibrium with water in which the amine becomes protonated and hydroxide is produced Basicity of Amines

  23. Loss of the N–H proton requires a very strong base Amines as Acids

  24. Ammonia and other amines are good nucleophiles Synthesis of Amines SN2 Reactions of Alkyl Halides

  25. Uncontrolled Multiple Alkylation are Unavoidable when Sterically Un-hindered Amines React

  26. Reduction of nitriles and amides

  27. Arylamines are prepared from nitration of an aromatic compound and reduction of the nitro group Reduction by catalytic hydrogenation over platinum is suitable if no other groups can be reduced Iron, zinc, tin, and tin(II) chloride are effective in acidic solution Reduction Aryl Nitro Compounds

  28. Azide ion, N3- displaces a halide ion from a primary or secondary alkyl halide to give an alkyl azide, RN3 Alkyl azides are not nucleophilic (but they are explosive) Reduction gives the primary amine Selective Preparation of Primary Amines:the Azide Synthesis

  29. A phthalimide alkylation for preparing a primary amine from an alkyl halide The N-H in imides (-CONHCO-) can be removed by KOH followed by alkylation and hydrolysis Gabriel Synthesis of Primary Amines

  30. Carboxylic acid derivatives can be converted into primary amines with loss of one carbon atom by both the Hofmann rearrangement and the Curtius rearrangement Hofmann and Curtius Rearrangements

  31. RCONH2 reacts with Br2 and base to give electron deficient nitrogen Hofmann Rearrangement (Mechanism) Part I

  32. Hofmann Rearrangement (Mechanism) Part II Alkyl group (-R) migrates to the neighboring electron-deficient nitrogen. Hydration of the resultant isocyanate gives carboxamic acid.

  33. Hofmann Rearrangement (Mechanism) Part III Deprotonation-reprotonation produces a protonated ammonium zwitterion (a good leaving group). It’s elimination produces the amine and carbon dioxide by-product.

  34. Heating an acyl azide prepared from substitution an acid chloride This rearrangement also involves migration of R from C=O to the neighboring electron-deficient nitrogen with simultaneous loss of a leaving group Curtius Rearrangement

  35. Acylation leads to amides (1o, 2o, or 3o.) Reactions of Amines

  36. Converts amines into alkenes NH2- is very a poor leaving group so it converted to an alkylammonium ion, which is a good leaving group Hofmann Elimination

  37. Exchanges hydroxide ion for iodide ion in the quaternary ammonium salt, thus providing the base necessary to cause elimination Silver Oxide Is Used for the Elimination Step

  38. We would expect that the more highly substituted alkene product predominates in the E2 reaction of an alkyl halide (Zaitsev's rule) However, the less highly substituted alkene predominates in the Hofmann elimination due to the large size of the trialkylamine leaving group The base must abstract a hydrogen from the most sterically accessible, least hindered position Orientation in Hofmann Elimination

  39. Steric Effects Control the Orientation

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