19.2.1 Infrared (IR) Spectroscopy

• Infrared (IR) spectroscopy is used to identify functional groups within molecules
• The O-H functional group is typically found in the 3200-3600 cm^-1 region of an IR spectrum.
• Match the wavenumber range with the corresponding functional group:

  3200-3600 cm^-1 ↔️ O-H (alcohols, phenols)

  1650-1800 cm^-1 ↔️ C=O (carbonyl groups)

  1000-1300 cm^-1 ↔️ C-O (ethers, esters)
• IR spectroscopy identifies functional groups by measuring the absorption of infrared radiation
• A monochromator in an IR spectrometer is used to measure the intensity of radiation passing through the sample.

  False
• IR radiation interacts with molecules by exciting their vibrational modes.
• Match the wavenumber range with the corresponding functional group:

  3200-3600 cm^-1 ↔️ O-H (alcohols, phenols)

  1650-1800 cm^-1 ↔️ C=O (carbonyl groups)

  1000-1300 cm^-1 ↔️ C-O (ethers, esters)
• Each functional group in a molecule absorbs IR radiation at a unique wavenumber.
• IR spectrometers use infrared light to analyze the functional groups in a sample.
• What is the wavenumber range for the O-H functional group in alcohols and phenols?

  3200-3600 $cm^{ - 1}$
• The O-H functional group in alcohols and phenols absorbs infrared radiation at wavenumbers between 3200 and 3600 $cm^{ - 1}$
• The C=O functional group in carbonyl groups absorbs infrared radiation at wavenumbers between 1650-1800 $cm^{ - 1}$.
• What is the wavenumber range for the C-O functional group in ethers and esters?

  1000-1300 $cm^{ - 1}$
• Match the components of an IR spectrometer with their function:

  Infrared source ↔️ Generates a spectrum of infrared radiation

  Sample cell ↔️ Holds the sample to be analyzed

  Monochromator ↔️ Selects specific wavelengths

  Detector ↔️ Measures radiation intensity
• What is the function of the infrared source in an IR spectrometer?

  Generates infrared radiation
• The monochromator in an IR spectrometer selects specific wavelengths of infrared radiation.
• The detector in an IR spectrometer measures the intensity of infrared radiation
• What does the computer system in an IR spectrometer do?

  Processes and displays spectrum
• IR radiation interacts with molecules by exciting their vibrational modes
• Why does IR radiation create a unique pattern on the IR spectrum?

  Specific functional group absorption
• What is the primary goal of identifying vibrational frequencies in IR spectroscopy?

  Identify functional groups
• In IR spectra, characteristic peaks appear at specific wavenumbers
• IR spectroscopy measures the absorption of infrared radiation by chemical bonds.
• How does IR spectroscopy identify functional groups in molecules?

  Measures infrared radiation absorption
• The O-H functional group in alcohols and phenols absorbs infrared radiation at wavenumbers between 3200 and 3600 $cm^{ - 1}$
• Arrange the components of an IR spectrometer in the order that IR radiation passes through them:

  1️⃣ Infrared Source

  2️⃣ Sample Cell

  3️⃣ Monochromator

  4️⃣ Detector

  5️⃣ Computer System
• Match the functional group with its characteristic wavenumber range:

  O-H ↔️ 3200-3600 $cm^{ - 1}$

  C=O ↔️ 1650-1800 $cm^{ - 1}$

  C-O ↔️ 1000-1300 $cm^{ - 1}$
• What happens to a molecule when it absorbs infrared radiation during IR spectroscopy?

  Vibrational modes are excited
• The O-H functional group in alcohols and phenols exhibits a stretching vibration at wavenumbers between 3200 and 3600 $cm^{ - 1}$
• Interpreting IR spectra involves comparing characteristic peaks to standard wavenumber ranges.
• Match the functional group with its characteristic peak in IR spectra:

  O-H ↔️ Broad, strong peak

  C=O ↔️ Sharp, strong peak

  C-O ↔️ Strong absorption
• Why is IR spectroscopy valuable for identifying compounds?

  Recognizes functional groups
• The O-H functional group in alcohols and phenols produces a broad, strong peak at wavenumbers between 3200 and 3600 $cm^{ - 1}$
• The C=O functional group in carbonyl groups produces a sharp, strong peak in the IR spectrum.
• What does IR spectroscopy measure to identify functional groups?

  Infrared radiation absorption
• To identify a compound using IR spectroscopy, its spectrum is compared to known standards
• A sharp, strong peak in the IR spectrum at 1650-1800 $cm^{ - 1}$ indicates the presence of a C=O group.
• How is the compound's identity determined using IR spectroscopy?

  By matching observed peaks
• IR spectra differ between compounds due to the presence and types of functional groups they contain.
• Strong peaks in the IR spectrum indicate highly abundant functional groups.