Infrared Spectroscopy Functional Groups

Infrared spectroscopy helps identify functional groups in organic compounds by measuring their vibrational transitions. Each functional group has unique absorption peaks, revealing important information about molecular structure and properties, from alkanes to halides.

1. Alkanes (C-H stretch)

   • Characterized by single C-H bonds.
   • Absorption typically occurs around 2850-2960 cm⁻¹.
   • Peaks indicate the presence of saturated hydrocarbons.

2. Alkenes (C=C stretch)

   • Contains at least one double bond between carbon atoms.
   • C=C stretch appears around 1620-1680 cm⁻¹.
   • Indicates unsaturation in the molecular structure.

3. Alkynes (C≡C stretch)

   • Features a triple bond between carbon atoms.
   • C≡C stretch is observed around 2100-2260 cm⁻¹.
   • Peaks suggest the presence of unsaturated hydrocarbons.

4. Alcohols (O-H stretch)

   • Contains a hydroxyl (-OH) group.
   • O-H stretch appears broad around 3200-3600 cm⁻¹.
   • Indicates the presence of alcohol functional groups.

5. Carboxylic acids (C=O stretch, O-H stretch)

   • Contains both a carbonyl (C=O) and hydroxyl (-OH) group.
   • C=O stretch appears around 1700-1725 cm⁻¹; O-H stretch is broad around 2500-3300 cm⁻¹.
   • Peaks indicate acidic properties of the compound.

6. Aldehydes (C=O stretch)

   • Characterized by a carbonyl group at the end of a carbon chain.
   • C=O stretch appears around 1720-1740 cm⁻¹.
   • Indicates the presence of aldehyde functional groups.

7. Ketones (C=O stretch)

   • Contains a carbonyl group within the carbon chain.
   • C=O stretch appears around 1705-1725 cm⁻¹.
   • Peaks indicate the presence of ketone functional groups.

8. Esters (C=O stretch)

   • Contains a carbonyl group adjacent to an ether (-O-) group.
   • C=O stretch appears around 1735-1750 cm⁻¹.
   • Indicates the presence of ester functional groups.

9. Amines (N-H stretch)

   • Contains nitrogen bonded to hydrogen atoms.
   • N-H stretch appears around 3300-3500 cm⁻¹.
   • Peaks indicate the presence of amine functional groups.

10. Amides (N-H stretch, C=O stretch)

    • Contains both a carbonyl group and an amine group.
    • N-H stretch appears around 3300-3500 cm⁻¹; C=O stretch appears around 1650-1700 cm⁻¹.
    • Indicates the presence of amide functional groups.

11. Aromatic compounds (C-H stretch, ring vibrations)

    • Contains a benzene ring structure.
    • C-H stretch appears around 3030 cm⁻¹; ring vibrations occur in the region of 1400-1600 cm⁻¹.
    • Peaks indicate the presence of aromaticity.

12. Nitriles (C≡N stretch)

    • Contains a carbon triple-bonded to nitrogen.
    • C≡N stretch appears around 2210-2260 cm⁻¹.
    • Indicates the presence of nitrile functional groups.

13. Ethers (C-O-C stretch)

    • Contains an oxygen atom bonded to two carbon atoms.
    • C-O stretch appears around 1050-1150 cm⁻¹.
    • Peaks indicate the presence of ether functional groups.

14. Nitro compounds (N-O stretch)

    • Contains a nitro group (-NO₂).
    • N-O stretch appears around 1500-1600 cm⁻¹ and 1300-1400 cm⁻¹.
    • Indicates the presence of nitro functional groups.

15. Halides (C-X stretch, where X is a halogen)

    • Contains a carbon bonded to a halogen atom (F, Cl, Br, I).
    • C-X stretch appears in the range of 600-800 cm⁻¹, varying by halogen.
    • Peaks indicate the presence of halogenated compounds.