19.2.1 Infrared (IR) Spectroscopy

• What does infrared spectroscopy measure?

  Absorption of infrared radiation
• The principle of IR spectroscopy involves the absorption of infrared radiation by molecular vibrations
• Steps in the principle of IR spectroscopy

  1️⃣ Infrared radiation is shone through a sample

  2️⃣ Molecules absorb light at specific frequencies

  3️⃣ Chemical bonds vibrate, causing stretching and bending

  4️⃣ Absorption pattern is recorded
• What type of light is used in IR spectroscopy to excite molecular vibrations?

  Infrared radiation
• Vibrational modes in IR spectroscopy refer to the specific frequencies at which molecules vibrate.


  True
• The Fourier Transform in FTIR spectroscopy converts the interference pattern into a frequency spectrum
• What distinguishes modern FTIR spectroscopy from older dispersive IR instruments?

  Fourier Transform
• What does the interferometer in IR spectroscopy do to the infrared beam?

  Splits and recombines it
• Alkanes show a characteristic C-H stretch in the range of 2850-2970 cm⁻¹.


  True
• What is the typical IR absorption range for the O-H stretch in alcohols?

  3200-3600 cm⁻¹
• The presence of functional groups in a molecule can be identified by analyzing characteristic IR absorption peaks.


  True
• What does IR spectroscopy measure to provide information about molecular structure?

  Absorption of infrared radiation
• What determines the specific frequencies at which molecules vibrate in IR spectroscopy?

  Molecular structure and functional groups
• The infrared radiation source in IR spectroscopy generates light to excite molecular vibrations
• What are the two key features that distinguish modern FTIR spectroscopy from older dispersive IR instruments?

  Interferometer and Fourier Transform
• The C=O stretch in ketones typically occurs in the range of 1680-1750 cm⁻¹
• What does the overall pattern of absorption peaks in an IR spectrum reflect?

  Molecular structure
• The pattern of absorbed infrared light is unique to the molecular structure of a compound.


  True
• What type of molecular information does IR spectroscopy provide?

  Functional groups and structure
• IR spectroscopy can only analyze samples in solid form.

  False
• What determines the absorption pattern in IR spectroscopy?

  Molecular structure
• The principle of IR spectroscopy measures the absorption of infrared radiation by molecules, causing their chemical bonds to vibrate
• What is one application of IR spectroscopy?

  Compound identification
• Match the component of IR spectroscopy instrumentation with its description:

  Infrared Radiation Source ↔️ Generates infrared light

  Sample Holder ↔️ Holds the sample being analyzed

  Detector ↔️ Measures infrared light intensity

  Interferometer ↔️ Splits and recombines the infrared beam
• Which component in IR spectroscopy generates infrared light?

  Infrared Radiation Source
• What are the key features that distinguish modern FTIR spectroscopy from older dispersive IR instruments?

  Interferometer and Fourier transform
• The infrared radiation source in IR spectroscopy generates light to excite molecular vibrations
• The detector in IR spectroscopy measures the intensity of infrared light after it passes through the sample.


  True
• Match the functional group with its typical IR absorption range:

  Alkanes ↔️ 2850-2970 cm⁻¹

  Alkenes ↔️ 1620-1680 cm⁻¹

  Alkynes ↔️ 2100-2260 cm⁻¹

  Alcohols ↔️ 3200-3600 cm⁻¹

  Aldehydes ↔️ 1720-1740 cm⁻¹
• The C≡C stretch in alkynes appears in the IR absorption range of 2100-2260 cm⁻¹
• Match the functional group with its typical C=O stretch absorption range:

  Aldehydes ↔️ 1720-1740 cm⁻¹

  Ketones ↔️ 1680-1750 cm⁻¹

  Carboxylic Acids ↔️ 1680-1760 cm⁻¹

  Esters ↔️ 1730-1750 cm⁻¹
• The principle of IR spectroscopy involves measuring the absorption of infrared radiation, which causes chemical bonds to vibrate
• When a molecule absorbs infrared light, it transitions to a higher vibrational state.


  True
• The interferometer and Fourier transform are key features of FTIR spectroscopy.


  True
• The Fourier Transform converts the interference pattern into a frequency spectrum
• FTIR spectroscopy allows for faster data collection and improved signal-to-noise ratios compared to older IR spectrometers


  True
• Arrange the main components of an IR spectroscopy instrument in the correct order:

  1️⃣ Infrared Radiation Source

  2️⃣ Sample Holder

  3️⃣ Detector

  4️⃣ Interferometer

  5️⃣ Fourier Transform
• The presence of different functional groups in a molecule can be identified by analyzing characteristic IR absorption peaks
• What is the IR absorption range for the C-H stretch in alkanes?

  2850-2970 cm⁻¹
• Match the functional group with its characteristic IR absorption range:

  Alcohols ↔️ 3200-3600 cm⁻¹ (O-H stretch)

  Aldehydes ↔️ 2700-2900 cm⁻¹ (C-H stretch)

  Alkynes ↔️ 3300 cm⁻¹ (C≡C-H stretch)

  Alkenes ↔️ 1620-1680 cm⁻¹ (C=C stretch)