7.2.2 Interpretation of IR Spectra

• What does IR spectroscopy measure?

  IR radiation absorption
• In IR spectroscopy, each vibration mode corresponds to a particular bond
• The absorption wavenumber in IR spectroscopy is measured in cm⁻¹.
• What is the absorption wavenumber range for the O-H bond stretching vibration?

  3200-3600 cm⁻¹
• The N-H bond stretching vibration absorbs in the range of 3300-3500
• Match the bond type with its absorption wavenumber range:

  O-H ↔️ 3200-3600 cm⁻¹

  C=O ↔️ 1680-1750 cm⁻¹

  N-H ↔️ 3300-3500 cm⁻¹

  C-H ↔️ 2850-3000 cm⁻¹
• What happens to the bonds in a molecule when IR radiation interacts with it?

  They vibrate
• The x-axis of an IR spectrum represents transmittance (%)

  False
• The y-axis of an IR spectrum represents transmittance
• Which functional group is associated with a broad absorption peak in the3200-3600 cm⁻¹ range?

  O-H
• Steps to interpret an IR spectrum

  1️⃣ Identify the major absorption peaks

  2️⃣ Determine the corresponding bond types

  3️⃣ Match the bond types to functional groups
• The y-axis of an IR spectrum measures wavenumber.

  False
• The C=O bond stretching vibration absorbs in the range of 1680-1750
• Which type of compounds show an absorption peak in the 3200-3600 cm⁻¹ range?

  Alcohols
• What does an absorption peak at 3200-3600 cm⁻¹ indicate in an IR spectrum?

  Presence of O-H bond
• The C=O bond stretching vibration absorbs in the range of 1680-1750
• What is the purpose of analyzing absorption peaks in an IR spectrum?

  Identify functional groups
• By analyzing the absorption peaks in an IR spectrum, you can identify the functional groups
• An O-H bond in a molecule absorbs at a wavenumber range of 3200-3600
• What is the typical wavenumber range for the stretching vibration of a C=O bond?

  1680-1750 cm⁻¹
• The stretching vibration of an N-H bond in an amine absorbs at a wavenumber range of 3300-3500 cm⁻¹.
• The C-H bond in alkanes absorbs at a wavenumber range of 2850-3000
• What does IR spectroscopy measure?

  Absorption of IR radiation
• The y-axis of an IR spectrum represents transmittance
• The stretching vibration of an O-H bond in alcohols absorbs at the same wavenumber range as in carboxylic acids.
• Which functional group is associated with an absorption peak in the 1680-1750 cm⁻¹ range?

  C=O
• An N-H bond in amides absorbs at a wavenumber range of 3300-3500
• Which bond type absorbs at the highest wavenumber range in IR spectroscopy?

  O-H
• The C-H bond in aldehydes absorbs at a wavenumber range of 2850-3000 cm⁻¹.
• The stretching vibration of an O-H bond in alcohols is observed at 3200-3600 cm⁻¹.
• Which functional group absorbs at the lowest wavenumber range in IR spectroscopy?

  C-H
• Key bond types absorb IR radiation at specific frequencies
• The O-H stretching vibration in alcohols is observed at 3200-3600 cm⁻¹.
• What is the absorption wavenumber range for C=O stretching in ketones?

  1680-1750 cm⁻¹
• The N-H bond exhibits stretching vibrations at 3300-3500 cm⁻¹
• What type of compounds show C-H stretching at 2850-3000 cm⁻¹?

  Alkanes, Aldehydes
• An absorption peak in the O-H stretching range confirms the presence of an alcohol.
• Match the bond type with its corresponding absorption wavenumber range:

  O-H ↔️ 3200-3600 cm⁻¹

  C=O ↔️ 1680-1750 cm⁻¹

  N-H ↔️ 3300-3500 cm⁻¹

  C-H ↔️ 2850-3000 cm⁻¹
• Functional groups in molecules can be identified by analyzing the absorption peaks in an IR spectrum.
• At what wavenumber range does the C=O bond absorb IR radiation?

  1680-1750 cm⁻¹